523
FAULTS AND THEIR EFFECT
ON COAL
MINING
IN
ILLINOIS
W. John Nelson
Illinois Institute
of Natural Resources
STATE GEOLOGICAL SURVEY DIVISION
Jack A. Simon, Chief
CIRCULAR 523
1981
COVER PHOTO:
Herrin (No. 6) Coal offset by a high-angle normal
(AB) and
fault
Located
mine
in
in
a horizontal
bedding fault (CD).
the Cottage Grove Fault System, at a
southern
Ruler
Illinois.
is
6 feet long.
Mary Szpur
Editor:
Draftsman: Craig Ronto
Nelson, W. John
Faults and their effect
on
coal mining in Illinois.
-
Champaign,
III.
:
Illinois
State Geological Survey Division, 1981.
40
p.
:
ill.
Glossary:
1.
;
p.
28 cm.
39
Mines and mining.
2.
-
(Circular
/ Illinois
Faults (Geology).
I.
State Geological Survey
Title.
II.
Series.
Printed by authority of the State of Illinois (2,500/1981)
;
523)
FAULTS AND THEIR EFFECT
ON COAL
MINING
IN
ILLINOIS
W. John Nelson
ILLINOIS STATE
GEOLOGICAL SURVEY
Natural Resources Building
615 East Peabody Drive
Champaign, L
I
61820
CIRCULAR 523
1981
Digitized by the Internet Archive
in
2012 with funding from
University of
Illinois
Urbana-Champaign
http://archive.org/details/faultstheireffec523nels
5
1
CONTENTS
ABSTRACT
1
FAULTING-BASIC TERMS AND CONCEPTS
2
3A. Slickensides and mullion
3B. Slickensides on lower surface of shale
4.
Sample of breccia from Rend Lake Fault System
2
5.
Reverse fault
6
2
6.
Faults forming an en echelon pattern
8
faults
3
7.
Features of faults
4
8.
Origin of faults
6
faults
Displacement of coal seams
Weakening of roof in underground mines
Influx of water and gas along faults
8
10.
8
11.
Mining through a large fault
8
12.
Placement and angling of crosscuts
15.
Recognizing faults when drilling
12
16.
Seismic exploration for faults
13
17.
MINING
IN
FAULTED AREAS
TECTONIC FAULTS
OF ILLINOIS
IN
13
THE COAL FIELDS
14
Cottage Grove Fault System
15
Wabash Valley Fault System
Rend Lake Fault System
Du Quoin Monocline, Dowell Fault Zone,
and Centralia Fault
The Shawneetown Fault Zone
16
Faults in the Eagle Valley Syncline
Faults in southeastern Saline
Other tectonic
County
faults in Illinois
Coal
20.
Compactional
IN
Gravitational slumps and
slides
22
23
24
27
22.
26
26
23.
Geologic structures of
30
26
26
24.
Concretion
in
Fault Zone, Eagle Valley Syncline,
Illinois
28
33
35
27.
31
Sketch of a typical roll
Mineralized "goat beards" at a fault
35
38
Clay dike
in a
28.
32
in
the
32
in
surface
the Springfield (No. 5) Coal
mine
33
Vertical clay dike in black shale
above the
Springfield (No. 5) Coal in an underground
30.
31.
mine
Origin of clay dikes and clay-dike faults
Clay-dike faults
36
body
North-south cross section through the shear body at
the Orient No. 6 Mine
39
37
TABLE
1
.
33
34
34
Portion of the Orient No. 6 Mine showing outline
of the shear
32.
29
black shale above the Herrin (No. 6)
Coal
25.
Herrin (No. 6) Coal
REFERENCES
Fault nomenclature
Types of faults
21
25
RECOMMENDATIONS
FIGURES
20
Rend Lake Fault System, Du Quoin Monocline,
Centralia Fault, and related structures
29.
GLOSSARY
7
18
Shawneetown
28
Clay-dike faults
Wabash County
16
1
and associated structures
Crown II Mine of Freeman United Coal Mining Co.
COAL-BEARING STRATA
faults
in
1
21.
17
26.
NONTECTONIC FAULTS
OF ILLINOIS
14
Detailed structure of the top of the Herrin (No. 6)
11
mines
12
faulted area,
in a
19.
14.
in
1
strata
18.
11
Recognizing faults
10
where faults cross mine headings at right angles
Placement and angling of crosscuts in a faulted area,
where faults cross mine headings at oblique angles
Faults and related structures in southern Illinois
The Cottage Grove Fault System
Cross section of part of the Cottage Grove
Fault System
Major structures of the Wabash Valley Fault
System
Portion of Eagle No. 2 Mine of Peabody Coal Company
9
13.
RECOGNIZING AND PREDICTING FAULTS
9
Portion of the Orient No. 6 Mine, about 1000 feet
Rend Lake Fault System
Encountering faults when drilling
Determining the throw of a fault by comparing
11
Impurities in coal
Configurations of faults dangerous to mining
east of the
9.
EFFECTS OF FAULTS ON COAL MINING
2.
6
Definition of faulting
Nomenclature of
Types of
1.
5
5
Characteristics of tectonic
and nontectonic
faults
FAULTS AND THEIR EFFECT
ON COAL
MINING
IN
ILLINOIS
ABSTRACT
Faults are fractures in the earth's crust along which move-
ment
They
(slippage) has occurred.
are
one of many types
of geologic disturbances that affect coal seams.
which are
common
erable effects
seams of
in coal
on coal mining, such
Illinois,
Faults,
have consid-
as: offsetting
of the coal
seams, creation of grades too steep for mining equipment to
follow, weakening of roof and ribs, admission of water and
gas
into
workings, and
introduction
of
clay
and other
impurities into the coal.
Faults can be grouped into tectonic faults, which are
caused by forces acting
hard rock deep within the earth,
in
which are formed by localized
and nontectonic
faults,
disturbance
incompletely
of
lithified
sediments.
The
presence of most tectonic faults can be predicted before
mining begins, and their location can be determined by
drilling, seismic
tonic faults,
exploration, and other means. Most nontec-
too small to detect or predict
in contrast, are
much beyond the working face.
The major systems of tectonic
faults in Illinois that
influence coal mining are located in the southern part of
the state.
They include the Cottage Grove, Wabash
Valley,
and Rend Lake Fault Systems, the Dowell Fault Zone and
Centralia Fault, the
in
Shawneetown Fault Zone, and
faults
the Eagle Valley Syncline. Smaller tectonic faults are
known or may exist in other coal mining areas of the state.
Many tectonic faults occur in regions where the rock layers
are folded, but
some
unfolded areas.
exist in
Nontectonic faults are found
in
every mine in the state,
although they are more troublesome
others.
The major
compactional
dikes),
classes
in
some
areas than in
of nontectonic faults include
faults, clay-dike faults (associated
and gravitational slumps and
by
faults are strongly controlled
rocks above a coal seam.
faults to lithology often
The
slides.
with clay
Many nontectonic
lithologic patterns in the
relationships of nontectonic
can be mapped so that the presence
of the faults can be predicted a short distance ahead of the
face.
Mining plans should be
adaptation to local conditions
FAULTS AND THEIR EFFECT ON MINING
IN ILLINOIS
as flexible as possible to
in
faulted areas.
allow
INTRODUCTION
paring a second report that will cover the other types of
geologic disturbances
many
Faults are responsible for
in
They cause major
Illinois.
losses
in
the coal seams of
Illinois.
mining
difficulties in coal
production; they
in
increase the danger, difficulty, and expense of mining; and
FAULTING-BASIC TERMS AND CONCEPTS
sometimes they force the abandonment of large blocks of
coal reserves, or even of entire mines. Every coal mine in
Definition of faulting
the state
affected to
is
some degree by
and some of
faults,
the most productive coal-mining areas are also the most
A
heavily faulted. Therefore, a better understanding of faulting
crust along
could be highly beneficial to the mining industry.
range from a barely perceptible
A
many
break
a
is
types of geologic disturbances
mining
interfere with
many people who work
Unfortunately,
and elsewhere possess
Illinois
in
Frequently,
coal measures.
in
discontinuities in the coal
all
and no attempt
are labeled as "faults,"
is
made to
identify
some
the true nature or origin of the disturbances. Thus
structures that are not true faults are mistakenly treated
which leads to improper mining procedure— often
with enormous costs
production, wasted effort, and
in lost
hazards to workers.
This
report
how
explains
defines
are presented in
this report
many
their
effects,
optimum mining
in
faulted
maps and
text,
and unmined areas where
be expected to occur are identified. Although
aimed primarily
is
at the
mine operator
in Illinois,
glossary of terms related to faults
is
included
in
the
This report does not cover
faulting or present
in
Illinois.
the technical aspects of
all
the details
all
known about
the various
For more complete discussions
of individual fault systems, the reader should consult the
other published reports available on these systems.
the
more recent
Joints are fractures along which noslippage has occurred.
Joints
Among
Bristol
and Treworgy
on the Wabash Valley Fault System; and Keys
and Nelson (1980) on the Rend Lake Fault System. Faults
(1979)
Centralia
and igneous dikes
are
in
discussed
by
County
Saline
Brownfield
(1954),
the joints
should consult Krausse et
al.
are available either free or
Survery
on
hard,
all
brittle
Some
of
are frequently called cleat. Joints can have
in coal
on coal mining, but since they do not
Some
sidered any further in this report.
are covered
in
discussed
my upcoming
in
and
rocks,
coal and black shale.
in
produce slippage, they are not faults and
Krausse et
will
not be con-
features of joints
(1979); joints also will be
al.
paper on disturbances
in coal
seams not related to faulting.
Nomenclature of
The
faults
surface of a fault, along which slippage has occurred,
known as the
but commonly
is
fault surface.
it
is
A
fault plane
a
a
map
(ISGS).
structural
Among
geology,
the
Billings
many
general
(1954),
Hills
(1963), and Spencer (1969) are suggested.
This report deals only with true geologic faults (the
results of slippage along fractures in the earth).
I
am
pre
is,
it
is
The
orientation of a
terms of strike and dip
the direction
in
(fig.
1).
the plane of
shown by the
on
fault
do not have a strike). The dip is
plane makes with a horizontal surface.
to 45° often are called low-angle
Faults with a dip of
those dipping 45° to vertical are high-angle
faults;
On
fault
termed
is
can have any orientation,
the trend of a horizontal line
the angle the fault
is
known
a fault
from mining
faults.
with an inclined plane, the block above the
and the block below
called the hanging wall,
footwall
as the
practice,
(fig.
and
1).
is
These terms are derived
refer to
the fact that in an
entry (tunnel) intersected by a fault, the miner would have
hang him.
State
in
be curved,
it
(horizontal faults
his feet
Illinois
is
the fault; that
by Clegg
(1979). All of these reports
on loan from the
strike
described
is
may
fault surface
planar or nearly so; then
a fault plane (fig. 1). Fault planes
discussion of clay-dike faults and clay dikes, the reader
textbooks
almost
in
pronounced
significant effects
thorough
are covered
(1955) and Clegg and Bradbury (1956). For
Geological
found
are
are especially
reports are: Nelson and Krausse (1981)
on the Cottage Grove Fault System;
around
two.
The
back of this publication.
systems
movement
or any combination of the
lateral,
ranging from horizontal to vertical.
fields as well.
fault
may be up and down,
fault systems in the coal fields of Illinois
of the principles presented are valid for other coal
A
miles.
they can be identified and predicted, and
The major
faults can
describes
faults,
suggests procedures to ensure
areas.
many
to
have moved relative to one another. The
will
a limited under-
standing of the variety of geologic disturbances that affect
as faults,
amount
that has been faulted will be broken, and the broken pieces
geologic terms,
interrupt coal seams and
in
the earth's
which slippage or displacement has occurred.
operations.
mining
in
which slippage has occurred. The slippage may
Faults produce displacement of rock layers; a coal seam
in
Faults are only one of
that can
defined as any break or fracture
is
the earth's
fault,
crust along
fault
on the footwall, and the hanging wall would over-
The term
slip
denotes the
relative
displacement of
formerly adjacent points on opposite sides of
(fig.
1).
surface
The
in
total
the
amount of
direction
of
slip,
movement,
The
net slip can be resolved into
slip
(horizontal,
parallel
to
to the dip of the fault plane).
is
the
net
two components:
strike)
Two
a fault surface
measured along the
and
dip-slip
slip.
strike-
(parallel
additional terms used to
describe displacement of faults are throw and heave
ILLINOIS STATE
fault
(fig. 1).
GEOLOGICAL SURVEY CIRCULAR
523
Hanging wall
Figure
1
Throw
Where A and B
.
is
formerly
the
are points that were adjacent prior to faulting,
= net
points,
component of separation
and
heave
for the
horizontal
the
is
same two
points.
Throw
slip,
A
component of separation of two
vertical
adjacent
AB
BC
= strike
fault
strike-slip
direction
slip,
is
movement
of
fault
plane
defined
as
inclined
AC
is
(fig.
= dip
a
strike of the fault.
observer standing along the
faults
right-lateral fault.
him,
Faults can be classified according to the geometric orien-
movement
tation of the fault plane and the direction of
(fig. 2).
The
fault plane in a
normal fault
to the vertical and the hanging wall has
relative to the footwall.
of the earth's crust
is
inclined
moved downward
right-lateral
faults indicate an extension
the hanging wall
For
moves downward under the influence of
normal faults are sometimes termed
this reason
reverse fault
(fig.
relative to the
footwall. Reverse faults are generally caused by compression
of the
earth's
crust.
faults, particularly
A
is
In
90
fault with
Sometimes they
when
a
are termed thrust
the dip of the fault plane
and
vertical plane
vertical
is
shallow.
movement
technically neither a normal fault nor a reverse fault.
most cases the dip of the
.
It
is
metrically
not
uncommon
normal
in
one
fault plane will deviate
for the
place,
same
and reverse
FAULTS AND THEIR EFFECT ON MINING
from
fault to be geo-
IN
in
another.
ILLINOIS
to
an
and looking along
its
left-lateral.
fault
the
a left-lateral fault.
wrench
called
If,
moved toward him, it is a
left-hand block has moved toward
Strike-slip faults are caused
best-known
by wrenching action about
faults.
faults,
Many
of the
and are sometimes
world's
largest
such as the San Andreas Fault
and
in Cali-
fornia, are strike-slip faults.
In
slip
many
and
shows components of both strikemovement. Such faults are called oblique-
cases a fault
dip-slip
slip faults
(fig.
1).
Careful examination of the fault occa-
sionally allows a determination of the relative proportion
2B) has an inclined plane along
which the hanging wall has moved upward
or
block has
of horizontal and vertical
gravity faults.
A
If
= heave.
on which the primary
a vertical axis in the crust of the earth,
perpendicular to the strike of the
Tension causes the rock layers to rupture, and
fault plane.
gravity.
Normal
2A)
(fig.
it is
DC
= throw,
The movement may be
2C).
further
Types of
fault
AD
horizontal along a vertical or
and heave are measured along planes perpendicular to the
strike, the right-hand
slip,
In
layered rocks,
movement.
movement can occur along bedding
planes in the rock to produce a bedding fault
Movement along bedding
planes
may occur
(fig.
2D).
within one
rock unit, such as a coal seam, or at the boundary between
two rock
units.
Bedding
nize because there
A
is
faults are often difficult to recog-
no apparent offsetting of the
layers.
thin zone of crushed or broken rock or coal along the
may
be the only indication of a bedding
fault
surface
fault.
Bedding faults can turn into thrust
faults that cut across bedding.
faults or
normal
Figure
2.
Types of
seldom
Faults
Normal
faults. (A)
occur
fault; (B) reverse fault; (C) strike-slip
singly.
Many
large
faults
are
expressed as fault zones, which are composed of numerous
small faults and fractures that penetrate a zone of broken
rock.
Fault zones vary from a few feet to hundreds of
On a larger scale are fault systems, which are
many faults or fault zones. Some fault systems
feet in width.
composed
of
consist of a series of similar, parallel faults.
Examples
in
Illinois include the
Rend Lake Fault System and the
Wabash Valley Fault System, both of which consist of
many
are
parallel high-angle
normal
orientations,
Cottage
Grove Fault System
example of
a
faults.
faults that
in
southern
complicated fault system.
It
Illinois
is
an
includes a fairly
continuous, large master fault that strikes roughly east-west,
which
which
slip,
is
flanked by
strike
many
smaller subsidiary faults, most of
northwest-southeast. Normal, reverse, strike-
and bedding
oblique-slip,
faults have
all
been recognized
within the Cottage Grove Fault System.
are
characteristically
may
be useful
amount of
slip.
Slickensides
in
found
along
fault
determining the direction and
(figs.
3A
a right-lateral fault); (D)
bedding
fault.
by the
movement. Slickensides may be obliterated by
minor adjustments of movement along a fault, and so may
record a minor, final movement that differs from the net
slip. On some faults larger parallel furrows may occur, with
amplitudes ranging from inches to
known
as mullion.
erased
by
are rare
on
movement
later
Fault breccia
rock set
in a
a
claylike
Gouge and
Such furrows
are
as
are slickensides, but they
(fig.
4) consists of angular
fragments of
matrix of finely ground material found along
a fault surface.
with
feet.
Large-scale mullion are not as easily
faults in Illinois.
Gouge
consists of pulverized rock, usually
consistency,
found
in
the same setting.
breccia are the result of grinding of rock between
the walls of the fault as
movement
occurs. Large faults
generally have wide zones of gouge or breccia or both.
In
many
fragments
cases minerals have filled
in
open spaces between
the gouge zone, as well as fractures
most
common
many
parts of the world, valuable ore minerals are
minerals in fault zones
within fault zones.
planes and
is
friction of
Illinois
features
example
in
the
rocks bordering the fault zone. Calcite and quartz are the
Features of faults
Some
(this
surfaces with grooves or striations that are caused
Other fault systems
show a variety of
magnitudes, and types of movement. The
more complex, and include
(wrench) fault
and 3B) are polished
occurs as
Much
fillings
of the fluorspar
in
mined
Friction along a fault surface
slip.
in
may
in
found
southern
cause the rock layers
in
the direction
Such folding of the rocks abutting
ILLINOIS STATE
but
along faults.
adjacent to the fault to be bent or folded
of net
Illinois,
a fault
GEOLOGICAL SURVEY CIRCULAR
is
523
Figure 3A. Vertical fracture
slickensides
in coal to left of ruler shows horizontal
and small-scale mullion, indicating strike-slip
movement.
Figure 3B. Slickensides on lower surface of shale
FAULTS AND THEIR EFFECT ON MINING
IN
show
ILLINOIS
that a bedding fault exists at the contact of coal and roof.
Figure 4. Breccia— sample
Rend Lake
from
Fault System shows
angular fragments of dark limestone
(left) moved up
and the coal was bent downward
Figure 5. Reverse fault in which the hanging wall
relative to the footwall,
matrix of white,
in a
along the fault plane, resulting
crystalline calcite.
in
(From Nelson
drag.
and Krausse, 1981.)
called drag, and can be a useful indicator of the direction
of slip
(fig.
Not
5).
all
may
faults the rocks
faults display drag;
however,
it
is
so brittle.
is
faults
and
(table
1).
normal faults show no drag because the blocks are being
pulled
away from each other by extensional
so the friction
is
less
forces,
than on reverse (compressional) faults.
Furthermore, on some small normal faults the layers
be bent opposite the direction of
false drag.
slip,
Nonetheless, where drag
one of the most
and
forming what
is
present
it
is
may
called
provides
reliable indicators of the direction of slip.
distinguishing
and
have
criteria.
into
faults.
classified
in
a
according
For the purposes of
two broad
miles along strike.
They
are
many
and some may penetrate the entire crust of
layers,
the earth. Most tectonic fault systems consist of hundreds
or
thousands of individual fractures, with displacements
ranging
largest
from
in
fraction of an
a
inch to
many
have displacements of
Illinois
Tectonic faults include
miles (the
few thousand
a
the types of faults
all
we
have
many
to
different
this report faults are divided
categories: tectonic faults
and nontectonic
and mostly affect rocks that are
Usually tectonic faults can be projected into
fully hardened.
unmined
Nontectonic faults are formed when stresses affect
areas.
sedi-
ments while they are being transformed into rock; these
faults.
Tectonic
variety of processes,
Tectonic faults are formed by forces acting over
large areas,
faults
well-defined systems
discussed, including normal, reverse, strike-slip, oblique-slip,
have their origins
been
many
for
in
usually not limited to any specific rock type, but cut across
and bedding
can
them from nontectonic
Tectonic faults occur
may extend
that
feet).
Origin of faults
Faults
face.
Several characteristics are useful in recognizing tectonic
Many
be sheared off quite cleanly. Coal
often sheared without drag because
ahead of the working
are difficult to predict
faults
some
in
are
faults
planar
to
slightly
curved
and
generally follow straight courses, cutting across the boundaries
The
between different rocks with
faults are
commonly composed
en echelon fractures
(fig.
6).
or no deviation.
little
of
many
parallel or
Large tectonic faults
may
have wide zones of gouge and breccia, and the rocks adjacent to the fault
may
be brecciated. Drag
or normal, with strata bent
false
drag
is
in
is
either absent
the direction of net
slip;
rare.
ILLINOIS STATE
GEOLOGICAL SURVEY CIRCULAR
523
TABLE
1.
Characteristics of tectonic and nontectonic faults
Nontectonic faults
Tectonic faults
Highly variable
well-defined systems
Occurrence
In
Length
Up
to hundreds of miles
Displacement
Up
to
many
A few
thousands of
feet to
feet, rarely miles
Usually under 3 feet, rarely up to hundreds
miles
of feet
(net slip)
and dip
Fault surface
Planar to slightly curved
Often strongly curved both
Types of
Normal, reverse,
and bedding
Predominantly normal, some bedding
faults
Patterns on
Gouge or
map
breccia
strike-slip, oblique-slip,
Generally form parallel or en echelon sets
Curving, follow boundaries between rock types
Usually wide zones
Narrow zones or absent
Consolidated rock, basement rocks
Place of origin
faults,
rarely reverse faults
Absent to well-developed normal drag
Drag
in strike
False drag
a
may be developed
Unconsolidated or partially consolidated
sediments
Generally cross lithologic boundaries with
Lithologic control
little
Mode
Curving, tend to follow lithologic boundaries
or no deviation
Regional stresses, often from deep within
of origin
the earth;
movement on
Gravitational stress, loading, and differential
compaction; some may be triggered by
tectonic faults can
cause earthquakes
unmined
by
a
earthquakes
Often can be projected for miles into
Predictability
areas;
many can be
to locate
drilling
Basement = Precambrian igneous and metamorphic rocks that underlie the
14,000 feet below the surface (Willman et al., 1975).
Tectonic faults develop
which are major forces
in
response to tectonic stresses,
the interior of the earth— the
in
more than
Difficult to predict
few
a
feet to
tens of feet ahead of the working face; difficult
located
sedimentary rocks.
faults
by
drilling
In Illinois
the basement
the coal-bearing strata of
in
relatively
small, with
Illinois,
is
2,000 to
however, are
few tens to hundreds
lengths of a
sort of forces that are responsible for building mountains.
of feet and net slips ranging from a few inches to several
Tectonic stresses are the primary cause of earthquakes
feet.
in
most parts of the world. This
that
all
since
not to say, however,
is
tectonic faults present a danger of earthquakes,
many
of these faults were formed millions of years
contrast to
In
tectonic
which are
faults,
and planar, most nontectonic
straight
strike or dip, or both.
relatively
faults are curved in
Nontectonic faults are usually con-
ago and are no longer active. None of the tectonic fault
fined to a single bed or stratum, such as the coal seam or
systems that penetrate coal-bearing strata
a
known
in
Illinois
are
to be active today.
Tectonic faults
Illinois are
known
concentrated
bed of shale
faults
in
to exist
in
the coal fields of
the southern part of the state,
in
bedding
in
the roof.
Illinois are
faults.
The
normal
great majority of nontectonic
faults,
which
locally
become
Reverse faults are rare, and strike-slip faults
of nontectonic origin are not
known
to exist in the state.
and include the Rend Lake, Cottage Grove, and Wabash
Usually,
nontectonic faults have
Shawneetown Fault Zone,
breccia,
although the surfaces of some are coated with
Valley Fault Systems and the
among
others.
calcite, pyrite,
Nontectonic faults do not occur
in
systems that can
be traced continuously through large areas; rather, their
occurrence and distribution are controlled by local factors.
Nontectonic faults are very
are
found
in
every
necessarily small
coal
common and
mine
in
widespread, and
Illinois.
They
are
not
Some can be traced along strike
and may have net slips measured in
faults.
for thousands of feet
tens to hundreds of feet.
The
vast majority of nontectonic
FAULTS AND THEIR EFFECT ON MINING
IN
ILLINOIS
little
or no gouge and
and other minerals. Drag may develop, often
as false drag opposite to the direction of slip.
Most nontectonic
partially
Some
consolidated
faults
develop
sediments,
in
unconsolidated or
and not
in
hard rock.
nontectonic faults result from gravitational stresses
caused by loading of sediments. Other nontectonic faults
result
various
from
differences
in
the
sediments such as peat,
processes that
of compaction of
mud, and sand. Other
rates
may produce nontectonic faults are:
expulsion
and
introduction of
(4)
including
impurities,
and
clay
various forms of mineral matter, into coal seams.
Displacement of coal seams
much
Faults in Illinois displace and offset coal seams by as
hundred feet
as several
vertically.
been eroded at the surface
in
deep for profitable recovery
underground
workings,
mining through
may
operator
a faulted zone, the
In strip
find the coal seam has
upthrown blocks, or is too
downthrown
in
large
faults
blocks.
very abusive to equipment designed
through rock, which
is
for mining in coal.
Because haulage roads and belt
must be kept within
a specified gradient, large
may
rock
In
mining
necessitate
lines
volumes of
have to be blasted, removed, and disposed of,
either to the surface or to old workings. Faults frequently
force the operator to change the layout of his mine, and
leave behind blocks of coal that
cannot be reached without
excessive cost.
Another source of
pitching
coal
in
difficulty
faulted
is
steeply
dipping or
For example, along the
areas.
Cottage Grove Fault System in southern Illinois, inclinations
exceeding 20° have been encountered in several places.
Mining equipment used
in flat-lying
in Illinois
designed for operation
is
seams; shuttle cars, mantrips, and other vehicles
have great difficulty on slopes steeper than
smooth conveyor
belts will
1
5°,
and standard,
not work when
above
tilted
18°. Several sizable blocks of coal have been left
unmined
because of steep dips along the Cottage Grove Fault System.
Figure 6.
Faults forming an en echelon pattern. The mine workings
above are to be extended west of the fault zone. If plan A
is followed— driving straight through the fault— much rock
must be mined and the haulageways must be graded. To
compensate, plan A minimizes exposure to unstable roof
the fault zone. In plan B the entries are turned parallel
in
between two
to the faults and driven through the gap
en echelon
faults,
and no grading
in
rock
is
necessary.
Weakening of roof
Any
in
underground mines
fault or fracture tends to decrease the stability of the
roof and ribs
danger
to
in
underground coal mines, and produces added
workers,
production of coal, and
decreased
increased expense for supports and for cleaning of
Faults are natural planes of separation in rock.
The
falls.
slicken-
However, many small fractures parallel with the faults
and the entries are likely to be present, and may render
sided "slip" with barely perceptible displacement can be as
roof control difficult.
hazardous as the major fault with
in
a
displacement measured
tens of feet.
Certain configurations of faults relative to the mine
of water from peat and other sediment, collapse of caverns
in
limestone, migration of salt and clay under overburden
pressure,
and shaking of the ground by earth tremors
caused by slippage along tectonic
faults.
opening are especially dangerous. One of the worst
"coffin cover"
7A), where
two
on
coal
number of
effects,
a fault strikes along
the entry
almost always undesirable,
mining. These effects include:
(1)
physical dis-
placement of coal seams, which may make them
difficult
(fig.
one
rib line,
and dips away.from
rib.
A
fall
by bolting through the
fault to tie the footwall
less
for the influx of water
opening of pathways
and gas into underground workings;
be pre-
to the
hanging wall. The opposite situation, where a fault along
the rib dips toward the center of the entry
(3)
may
vented by placing cribs or timbers under the footwall, and
and
underground workings;
the
7B). This leaves the footwall as a cantilever,
or impractical to mine; (2) reducing the stability of roof
ribs in
is
above
The wedge-shaped block of rock
below the junction of the faults is likely to fall as soon as
the coal is removed. Almost as hazardous is the situation
prone to break near the opposite
Faults have a
faults intersect
the middle of the entry.
where
EFFECTS OF FAULTS ON COAL MINING
(fig.
(fig.
dangerous because the weight of the roof
supported by both
is
7C),
is
evenly
pillars.
ILLINOIS STATE
GEOLOGICAL SURVEY CIRCULAR
523
The
spaced
closely
fractures
with
associated
many
tectonic fault systems present special problems for roof
When
control.
the roof
is
adjacent to large faults,
it
fre-
many parallel vertical or steeply dipping
fractures, which may be spaced less than an inch apart.
Such fractures can make roof control extremely difficult,
quently contains
especially
weak
a
if
rock, such as shale or thinly laminated
many
sandstone, overlies the coal. In
two
cases
intersecting
of fractures are present. Along major dip-slip faults,
sets
one
set of fractures often trends parallel to,
set
perpendicular
main
the
to
faults.
accompanied by two
are usually
and another
Strike-slip
faults
sets of fractures striking
obliquely to the master fault.
some
In
weakness
in
areas of Illinois the roof exhibits a preferential
one direction that may be related to adjacent
fault systems, even
though no
planes
slip
in
Franklin and Jefferson Counties
headings
may
be visible
in
Rend Lake Fault System
the roof. Along the north-trending
(fig.
north-south
8),
mines are more prone to roof failure than are
in
phenomenon occurs all along the
some cases the effect has been noted
more than 5 miles (8 km) east of the known faults. The
effect seems to be more pronounced east of the Rend Lake
Fault System than west of it, and is most intense immeeast-west headings. This
and
fault zone,
in
adjacent to the faults.
diately
Few
of the roof failures
can be attributed to any visible north-trending fractures
roof or coal. Rather, the instability usually
development of
along
the
a
center
is
"kink zone," or general
line
the heading.
of
appears soon after mining, and,
left
if
first
line
of roof sag
The"kink zone"
unattended, leads to
slabby breakage of the lower layers of rock (gutter
and eventually to massive
The
failure of the
difficulty resulting
from
may be minimized by
failure
headings
zones."
parallel
In
a
this
in
shown by
main
falls),
roof.
type of directional
avoiding placement of the
M£H
!
the direction of fractures or "kink
to
room-and-pillar
operation,
operators
the
should consider laying out the mine with main headings and
panels at a 45° angle to the line of failure. In most of Illinois,
mines have been
laid
out with headings trending north-south
and east-west because property boundaries generally run
in
these directions. In areas where directional roof failures are
a
Figure 7. Configurations of faults dangerous to mining. (A) "Coffin
problem, this practice should be reevaluated.
cover" pattern, which occurs when two faults intersect
above the center of the opening, is very dangerous. The
wedge of rock below the faults is likely to fall before roof
Influx of water and gas along faults
supports can be placed. (B) Fault near one rib that dips
Occasionally, difficulties are caused by the flow of water or
toward
pillar leaves
faults.
Some
far rib,
and prone to
pathways for the movement of
fluids
flammable gases into underground mines along
faults provide natural
the footwall supported only on the
fault or timbering or
failure.
both
Prompt bolting through the
may
prevent a
near one rib that dips toward the entry
through the crust of the earth, but others act as barriers
to the
movement
of water.
has been reported along
fields of Illinois,
great
Some
all
seepage of gas and water
the major faults
in
the coal
but only locally have the volumes been
enough to hinder mining.
An example
of water influx along a fault zone was
recently reported in the
Coal Mining
Company
Crown
in
II
Mine of Freeman United
Macoupin County (Nelson and
FAULTS AND THEIR EFFECT ON MINING
IN
ILLINOIS
to produce a roof
is
fall
than
A
or B.
evenly supported over the
is
fall.
pillars,
fault.
A
fault
less likely
so normal bolting
should suffice, although small slabs of rock
away along the
(C)
much
The weight of the roof
may break
Figure 8. Portion of the Orient No. 6 Mine, Freeman United Coal Mining
System. Although few faults were observed
with the faults. (From Krausse et
Nance, 1980). The main fault
fracture
of
small
probably of tectonic origin.
fault
are
a
large
On
in
main
fault,
coal.
from the main
parallel
is
not great, but
is
difficult to
pump
because the flow
is
centrated in one place, according to Nelson and Nance.
fractures that
trend
fractures are
most intense near the
Water and locally small amounts
mine along the strike-slip fault and along
the northeast-southwest fractures. The volume of water
fault.
(300 m) east of the Rend Lake Fault
both sides of the main
but some extend more than 1,000 feet away
of gas enter the
feet
and "kink zones" dominantly extend north-south
widely dispersed through the mine rather than being con-
number of open
The
falls
and
trending east-west,
northeast-southwest and penetrate water-bearing sandstone
above the
Company, about 1000
the study area, roof
1979.)
a left-lateral, strike-slip
is
displacement,
al.,
Minor influxes of natural gas and crude
observed
in several coal
oil
have been
mines, especially along the Cottage
Grove and Wabash Valley Fault Systems
in
southern
Illinois.
The presence of oil provides a clue that some of the gas
may be coming from underlying Mississippian or older
strata,
which the
faults are
known
to penetrate (Bristol
and Treworgy, 1979). Some gas may have originated
ILLINOIS STATE
GEOLOGICAL SURVEY CIRCULAR
in
523
by the
various coal beds cut
one
faults. In at least
sudden outburst of methane from
a fault
case, a
reached explosive
concentration and forced evacuation of the working face
supplementary
until
could
ventilation
be
established.
Impurities in coal
impurities detrimental
Various
common unwanted
most
to
mining and coal
coal
The
into coal seams along faults.
quality are introduced
materials are gouge and breccia,
sand, clay, pyrite and other sulfides, calcite, and quartz.
These minerals increase the ash and sulfur contents of the
and may cause accelerated wear and tear on mining
coal
equipment.
Some
faults are
pathways for water. Water can carry
amounts of clay and dissolved mineral matter and
deposit these materials in the coal seam. Deposits on
large
tectonic faults in Illinois are normally limited to a thin film
or growth
of clay
of
or quartz crystals
calcite,
pyrite,
The deposits
along fractures.
inconspicuous
usually
are
and widely dispersed, so they do not have much effect
on the
from a mine. The
some nontectonic faults, however,
unwanted clay in the coal.
overall quality of coal shipped
clay dikes associated with
can be a major source of
Occasionally, zones of highly crushed or pulverized coal
are encountered
a faulted area.
in
Mining such coal pro-
duces large amounts of dust and fine "slack." The dust
an environmental hazard, but the "slack"
a
problem today
as
it
was
was for lump and stoker
the days
in
is
not as great
is
when the main demand
coal.
RECOGNIZING AND PREDICTING FAULTS
Figure 9.
To
deal effectively with the problems caused
know how
mines, one must
by
how
to recognize faults and
normal fault (A), drag
In a
faults in
ment, and the
to
missing strata
(in
determine their orientation and amount of displacement.
fault (B), drag
is
Methods to
vation,
drill
of
drag
locate and predict faults include direct obser-
mapping and
features,
the
test
holes,
and the application of
this case the coal
In a reverse
bed).
again in the direction of
movement, and
hole from the surface encounters repeated strata.
cations
inconsistent
are
Another feature to look for
in
the direction of move-
or
contradictory,
should suspect there to be a large component of
geophysical (seismic) techniques.
Recognizing faults
in
analysis of related structural geologic
of
drilling
is
hole from the surface passes through
drill
mines
is
one
strike-slip.
slices— narrow slivers of
coal or rock in the zone of a large fault.
A
fault with slices
actually consists of multiple, roughly parallel fault surfaces.
A
problem
in a
arises
when
a fault
encountered unexpectedly
is
mine, and the operator needs to
how
and
cases
this
far the
coal
of the fault and the rocks
special training in
in
what direction
seam has been displaced.
by
be determined
can
know
geology
is
it
careful
a
penetrates
in
slip.
slip
Drag
(figs.
is
A
No
the area.
amount
often a useful indicator of the direction of
5 and
9).
Some
faults are rarely large
seam.
many
faults
false drag,
but such
enough to completely offset
clean-cut fault with
normal fault than
show
no drag
is
more
a reverse fault. In faults
FAULTS AND THEIR EFFECT ON MINING
a coal
likely to
where the
IN
thrown
thrown
the same direction as the
slice
of coal indicates that the seam
is
probably
upthrown across the main fault zone. Again, observation of
slices may not be reliable on a strike-slip or oblique-slip fault.
More
valuable
especially the latter.
ness test"
of
slip.
is
and
mullion,
a slickensided surface the
"smooth-
clues
On
are
occasionally helpful
slickensides
in
determining the direction
This test involves rubbing the palm of the hand along
the fault plane parallel with the slickensides,
be a
direction
indi-
smoother when the hand
ILLINOIS
in
net slip of the fault; for example, the presence of an up-
needed to recognize many of
the clues that faults leave about the direction and
of
In
examination
Slices will usually be
and then
in
the other.
is
moved
The
in
first
surface
in
will
the direction of
one
feel
slip-
—
'
page than
(ft)
400
-
effect
Siltstone
surface
the opposite direction. This
in
must be used with caution because
slip,
and not necessarily the major or net
the direction and
a large fault
a fault
The "smoothness
it
reveals the final
slip
of the fault.
amount of
displace-
ment can often be determined from examination of the
rocks on the far side of the fault. To examine these rocks.
one must first excavate through the gouge, breccia, and
slices into unbroken rock (not always easy or advisable
from the standpoint of safety). The strata at the far side
Limestone
1
1
rubbed
is
the direction of movement.
in
On
Shale
I
it
test"
Danville (No. 7) Coa!
-
when
caused by sharp tiny ridges that develop on
is
Siltstone
of the fault are then compared with those from nearby
exploratory
-
the seam
450 -
^^^^^_
Wfflif pi
/^>^>t
(fig.
Herrin (No. 6) Coal
answering questions. For example,
Underclay
System,
i
is
faults. Virtually
all
true
the
Rend Lake Fault
normal
are
faults;
system one can confi-
downthrown on the hanging
the case of large nontectonic
in
such faults
known
in Illinois are
normal
with the hanging wall downthrown.
when
drilling
Limestone
When
panies
^^^x
the methods described above have failed, coal comusually
to locate faults and determine their
drill
Harrisburg (No. 5) Coal
displacement. Drilling
is
done from within the mine to find
the coal. Test borings from the surface facilitate the detection of faults suspected to
500 -
Faults also
may
Driller's log
Roof
^^^"^
lie
ahead of the working face.
be predicted through well-planned, carefully
analyzed exploratory
Siltstone
ft
in
faults
large fault of this
a
Recognizing faults
——
Black shale
5
on
The same
faults,
Siltstone
i
known major
the
all
dently expect to find the coal
wall.
-i
10).
Knowledge of what has been previously experienced
with faults in a mine or in a district can be helpful in
Sandstone
"
and so on, to
overcasts,
falls,
Gray shale
therefore,
-
roof
cores,
determine whether they belong to the roof or the floor of
drilling.
^^^
Gray
\ *-*
shale
.^
nuiL'
^^
-i
\
^"^v
Siltstone
'\
'
Limestone
o'.\
Face of
I
^',V\
1
Herrin (No. 6) Coal
|
-
"Blue Band"
|-
1
^A
j
/
-
heading
\
Black shale
—
|
^A
^|
Floor
Cro
Figure 10.
s
section of
mine heading
ISGS 1981
by comparing strata. A fault has been encountered on a heading of a mine in the Herrin (No. 6)
is found on the far side of the fault. This coal cannot be the No. 6,
by black shale and limestone, whereas the No. 6 Coal has a roof of gray shale. Comparison with the
log of a nearby drill hole (left) shows that the coal across the fault is probably the Harrisburg (No. 5). The fault must be a reverse
fault, and the No. 6 Coal has been upthrown about 35 feet.
Determining the throw of
a fault
Coal. After driving through the gouge zone left to right, coal
however, because
it
is
overlain
ILLINOIS STATE
GEOLOGICAL SURVEY CIRCULAR
523
On
faults
spacing the geophones
indicated by such features as slickensided surfaces,
noise, using higher frequencies of sampling,
zones of gouge or breccia, and intensely fractured and
The broken rock
mineralized rock.
zone often
in a fault
is
can
be determined
still
logs or an
geophysical
if
accurate driller's log for the hole are available. Assuming
vertical
and roughly horizontal
holes
drill
as
strata,
usually the case in Illinois, normal faults are indicated
is
by
missing strata, and reverse faults by repeated strata in the
The vertical separation on the fault is the same
amount of missing or repeated section. When making
1
976; and Serres and Wiles,
accurately located
a
mine
maximum
the
recent
as coals,
black shales, or limestones should be used, rather than gray
which tend to be discontinuous or
shales or sandstones,
be found
in
A
the area under investigation.
holes
drill
likely to
large difference
the elevation of a coal bed between two holes does not
always indicate the presence of
Grove Fault System
in
500
in
Along the Cottage
a fault.
southern
Illinois
folded; dips of 10° to 20° are not
of 50 feet
may
uncommon. A
reflect folding, faulting, or a
of the two. In contrast, within the
may be
the strata
difference
two
the elevation of a coal bed between
feet apart
holes
combination
in
folded between faults, so
500
elevation within
a
difference of 50 feet
feet of lateral distance
may
safely
Most mining companies
tural
as a single solid line;
maps must
zone consists of
which the coal
slices in
Another
in Illinois
those
common
in this
a
series
who make and
manner.
Illinois
in
in
entries
in
is
cases a
a
set of
faults,
(fig. 6).
Mine
the line
in
if
the
oil
seismology have long been used by
and gas industry to delineate subsurface structures,
but such methods have only recently been applied to the
search for coal.
The
m) (Lepper and Ruskey,
(1
on
tests
made
has
and analog recording. At an underground mine
area
by
and
channel
sandstone-filled
a
several
properties of a system using vibroseismic sources
its
in
Illinois,
neighboring mined-out
a
were located seismically; these locations were confirmed
Similar features were
drilling.
method
two mines
at
by the same
located
Pennsylvania.
in
The
seismic data
could also be used to distinguish areas of thin or missing
from areas of normally developed
coal
al.,
(Coon
coal
et
1979).
The
drilling
advantage of seismic exploration over
greatest
that seismic testing provides a continuous profile,
is
whereas
companies can
coal
A
their
supply of
number of
holes that
drilled (Daly, 1979).
seismic
larities
an exploratory
in
increase
data and cut costs by reducing the
must be
By combining
provides only point data.
drilling
seismic studies with conventional coring
recently
involves
method
for locating faults and other irregu-
seams within
coal
in
Czechoslovakia
in
mine has been developed
1976). The method
small explosive charges at various
several
firing
a
(Stas,
locations in the mine, at the surface or in
drill holes,
and
monitoring the impulses from the shots on receivers placed
in
the mine around the area to be investigated.
experiments
other
involving
Two methods
other
obstructions
and
firing base
at distances
firing base to the receivers,
reflection of the
situated
receiver.
up to 2,600
The
conditions.
The
waves off of
ahead
of
radiation
method
alongside the
or
feet or even higher,
reflective
and the
faults or
method can be applied
is
under favorable
successful to roughly
in seismic
half that distance. Stas claims that either
exploration for coal have been promising. Researchers have
used to locate faults whose displacement
results of recent
tests,
16 feet (5 m), but
comparison, the smallest faults detectable by
In
shock waves from the
reflective
presence
its
USBM
of operation are available: one using direct radiation of
known.
Seismic exploration for faults
Techniques of
the
drilling. In
in
a sand-filled
Schwalb, 1979, personal communication).
nature can
stepwise fashion.
sometimes can be driven through gaps
is
their
use struc-
many
In
staggered in en echelon position along strike
the actual extent of the faults
on
of closely spaced parallel
downthrown
is
pattern
plot faults
only a few faults
realize that
be portrayed accurately
fault
southern Ohio,
equipment and techniques should
in
resolution of 3 feet
program,
be attributed to a fault.
maps
by seismic methods
faults
in
standard oil-field seismology are about 20 feet (Howard
Rend Lake or Wabash
Valley Fault Systems, the rock layers are seldom significantly
tilted or
mine
The Consolidation Coal Company
between adjacent
faults
knowledge of the structural conditions
requires
in
of
a
resolution was about
refinements
a
1976).
variable in thickness.
Recognition
two normal
Colorado. At
in
channel was identified on a seismic profile and
allow
marker beds such
977).
1
was subsequently confirmed by
log (fig. 9).
reliable
and improving
one experiment, the U.S. Bureau of Mines (USBM)
In
as the
the determinations,
closely, using filters to reduce
the processing of data (Peng, 1978; Lepper and Ruskey,
not recovered during coring, but the displacement of the
fault
more
cores obtained through drilling, the presence of
is
method can be
as little as 30
is
claimed that not only can depth, continuity, and sometimes
percent of the height of the coal seam. According to Stas,
thickness of seams
the system has been used with considerable success in a
be determined, but also that faults,
channels, major splits, and mined-out areas can be located.
Conventional
number of
Polish and Czechoslovakian coal mines.
seismology, usually designed for
oil-field
exploration at depths of several thousand feet, lacks ade-
quate resolution for work
in coal.
Modifications of equip-
MINING
IN
FAULTED AREAS
ment, techniques, and data processing must be made for
oil-field
fications
seismology to be suitable for coal. These modiinclude
using
less
intense
sources
FAULTS AND THEIR EFFECT ON MINING
IN
of energy.
ILLINOIS
Before any
location,
mining
is
attempted
direction, extent, and
in
a
amount
faulted area, the
of displacement
of the faults must be determined as accurately as possible.
The money spent on exploration can be recovered many
times over by the reduction
Where
in
best procedure generally
is
Upthrown
Downthrown
side
side
mining expenses.
or fault zone must be crossed, the
a large fault
Intake-
amount
possible distance. This minimizes the
ZUHCO F
air
to drive the headings at right
angles to the faults to cross the fault zone in the shortest
entries
of rock to
'
Roof control can be improved by
be excavated.
larger pillars
by
than are normally
avoiding
left,
headings
driving
Belt entry
leaving
with
parallel
several
mining through
in
mines
southern
major faults
Graded
in
The
which are part of the Rend Lake Fault System,
faults,
__/
Illinois
/.I
I
I
I
LJ
rock
I
- vj
'
pagc
!
11).
(fig.
in
-
nan cTsn
is
illustrated
in
.
,
Haulage road
and
faults
fractures.
Good procedure
I
and, insofar as possible,
e
trend nearly north-south and have throws of 20 to 45 feet.
\
The headings
that cross the faults extend east-west.
mains were mined
entries of a set of
up
The
t
The
to the fault
in coal
surface before the crossing was attempted.
belt
and
haulage entries were then driven through the fault zone,
Mining through a large
Figure 11.
along the
grading to the required angle. Intake and return-air entries
from
left
Rend Lake
fault,
as seen
many mines
in
Fault System. Mining advanced
to right.
were usually not graded, but were connected across the
by means of
faults
use
of
vertical or steeply inclined raises.
The
allowed maximum recovery of coal while
minimum amount of rock. The least number of
raises
mining the
needed to maintain ventilation were driven through
entries
the fault zone.
entries
and panels of most mines
due north, south,
run
generally
easier to support than
east,
north,
the span of mine opening that can be crossed by a fault.
compass works well in the
Rend Lake Fault System, but in other parts of the state,
faults do not run parallel with property lines. For example,
the Wabash Valley Faults of southeastern Illinois strike
whereas the faults
Cottage Grove Fault System of southern
Possibly the best plan
angle the crosscuts
The same
Illinois
in
the
show
a
faults at an
within
these
fault
systems are usually
(fig.
to both stagger the pillars and
is
12C).
principles apply
oblique angle
where
(fig.
entries cross a set of
13).
If
the crosscuts are
to be angled, they should be turned perpendicular to the
faults rather than parallel to
them. Staggering the crosscuts
can be helpful, provided that care
is
taken to ensure that
do not cut across intersections.
Where faults are numerous or trend in many
the faults
wide variety of orientations, northwesterly being the most
common. Mines
be driven at an angle to
and west, to minimize
south, east, and west. Mining
north-northeast,
four-way intersections. As
may
the direction of the faults. Angling the crosscuts minimizes
directly to the points of the
dominantly
and produces only three-way intersections,
a single fault,
in Illinois
the loss of coal around the boundaries of properties, which
also
by
which are
an alternative, the crosscuts
The main
are laid out
which reduces the length of heading that can be affected
as
the case with
is
many nontectonic
faults,
When
cannot be completely avoided.
directions,
mining along
designed so that entries and panels run parallel and per-
faults
pendicular to the major faults.
working crews should inspect the roof carefully for
Roof
stability
almost always suffers when mine openings
follow faults or fracture zones; for this reason, mining
along any fractures or faults should be avoided.
directly
The main
parallel
entries close to major faults should not be
with the
appear
faults,
extra supports as required. Several suggestions
install
on bolting and timbering
in
faulted areas are provided in
figure 7.
advanced
the entries. Often, the fractures are not
in
occurs,
Large faults are invariably accom-
faults.
panied by numerous smaller parallel faults and fractures
that
and
this
seen on the fresh face, and only become apparent
some time later, after the roof has already fallen.
The placement and angling of crosscuts is important in
TECTONIC FAULTS
OF ILLINOIS
IN
THE COAL FIELDS
easily
Figure
faulted areas.
12 shows desirable and undesirable
layouts of pillars for mining a set of headings through a
series
of
small
square grid
cut
across
(fig.
faults
12A)
several
roof failure.
One
at
is
a
right
angles.
Mining the usual
poor practice because faults can
intersections and crosscuts, producing
plan
is
to stagger the pillars
(fig.
12B),
Several major systems or zones of tectonic faults occur in
southern
there
Illinois
(fig.
Valley, and
and significantly influence coal mining
These include the Cottage Grove, Wabash
14).
Rend Lake Fault Systems, the Shawneetown
and Dowell Fault Zones, and the Centralia Fault. Smaller
unnamed
faults
also
are
numerous
Whereas no major tectonic
bearing
strata
faults are
in
southern
known
in
Illinois.
the coal-
north of Marion and Wabash Counties, a
ILLINOIS STATE
GEOLOGICAL SURVEY CIRCULAR
523
number of
small faults of possible tectonic origin have been
encountered.
Cottage Grove Fault System
More
mining has occurred along the Cottage Grove
coal
Fault System than along any other fault system
in Illinois.
At the present, four underground mines and two surface
mines are active within the faulted
and
area,
large reserves
of coal remain within the Cottage Grove Fault System
Saline, Williamson,
1
in
and Jackson Counties.
The Cottage Grove Fault System extends westward
from extreme eastern Saline County to at least as far as
northwestern Jackson County— a distance of 75 miles
The width of the zone ranges from 2 to 10 miles
15).
(fig.
and averages 4 to 5 miles. The
largest fault of the system,
designated as the master fault, trends west to northwest and
much
has as
side
In
feet of vertical displacement.
not consistent:
is
in
some
downthrown, elsewhere the south
is
least three places
of high-angle
along
is
downthrown.
two or more
fault
The master
trend.
its
direc-
apparently
or no vertical offset in at
little
normal and reverse
component of
large
side
The master
branches.
parallel
discontinuous, and has
The
places the north
areas the master fault splits into
several
roughly
is
200
as
throw
tion of
faults,
fault consists
probably with a
movement (Nelson and
strike-slip
Krausse, 1981).
Numerous northwest-trending
extend as
A
inches to
X
Displacements range from
far as 7 miles.
more than 50
subsidiary faults diverge
and
sides of the master fault
from the north and south
a
few
and generally, but not always,
feet
Most subsidiary faults are
few show reverse or oblique-
increase toward the master fault.
high-angle normal faults, but a
movement.
slip
accompanied
fractures, often
In
Saline
most
In
by
cases, large subsidiary faults are
numerous
smaller
parallel
and
faults
forming an en echelon arrangement.
County and extreme eastern Williamson
County, numerous dikes of igneous rock accompany the
subsidiary faults and present a hindrance to mining.
dikes are as
largest
notes).
The
known
blast.
Placement and angling of crosscuts
where
in
a faulted area,
mine headings at right angles. (A) Pilon square grid— large roof falls occur where
faults follow crosscuts and intersections. (B) Staggered
pillars— faults cannot follow mine openings for so long
lars
faults cross
laid
a distance, so large falls are less likely to occur than in A.
(C)
Staggered
pillar
and
angled
300
feet
as
material forming the dikes
mica-peridotite,
which
is
The
wide and 4 miles
is
field
a very hard rock
difficult
to
cut or
Frequently the coal on both sides of the dikes was
altered to
coke by the heat of the igneous rock that
in-
truded the coal (Clegg, 1955; Clegg and Bradbury, 1956).
The width of the coked zone ranges from a few inches to
many feet. The coked coal is usually mineralized and
has
little
value as a fuel.
Another factor complicating mining along the Cottage
crosscuts— probably
Grove Fault System
the best layout for this situation.
as
but most are smaller (Kay, ISGS unpublished
long,
Figure 12.
much
are
is
the presence of steep dips
close to the master fault.
coal
common;
in
in
the
Inclinations of 15° to 20°
the abandoned Old Ben Mine No. 15
in
Williamson County, the Herrin Coal reportedly dipped at
45
been
FAULTS AND THEIR EFFECT ON MINING
IN
ILLINOIS
close to the fault. Several sizable blocks of coal have
left
unmined because of
severe dips.
The
steep
tilts
Angled crosscuts
Crosscuts angled
away from
Staggered
pillars
Crosscuts at same
Faults taken up
Faults cross
angle as faults
in pillars
intersections or
faults
promote
nick corners of pillars
big falls
II'
oof
Placement and angling of crosscuts
Figure 13.
make
also
in faulted area
where
the calculation of reserves and projection of
mining plans from drill-hole data
Unless
a difficult task.
holes are closely spaced, one cannot be sure whether
drill
differences
faults or
in
between adjacent holes indicate
elevation
merely inclined coal seams.
mized with careful exploration. Figure 16
effective drilling
Mine
in
a
mine headings
faults cross
at oblique angles
normal
illustrates
an
85°. Faulted strata exposed
program that prepared the way for mining
segment of the master fault
at the Orient
No. 4
in
the coal mines display
may
large faults
be
tilted.
little
This fault
and numerous minor
In
the immediate
of the fault zone, water seepage has never been
observed; however,
an
increase
in
was
surface moisture
apparent.
Williamson County.
The
larger faults of the
by coal-test
Wabash Valley Fault System
faults are high-angle
and fractures that weaken the roof.
vicinity
et al., 1979).
with angles of dip that range from 50° to
faults,
drag, but beds in the fault zone
faults
(from Krausse
known
Herrin (No. 6) Coal. All the
zone consists of several
Disruptions to mining caused by faults can be mini-
through
fal
Coal
drilling.
Company
system can be located readily
At the Eagle No. 2 Mine of Peabody
Gallatin County, drilling disclosed the
in
presence of a large fault trending slightly east of north and
The Wabash
Illinois.
in
this
Valley
Although
area (particularly
Member), there has been
system
is
exposures
known
in
the
System
Fault
lies
in
large reserves of coal are
in
southeastern
known
to exist
the Springfield [No. 5]
little
coal mining to date.
Coal
The fault
primarily from drill-hole data and from
two underground mines currently
active in
lying just west of the slope
feet west of the slope to
farther north.
accurately
The Wabash Valley Fault System in Illinois extends
northeast from just north of the Shawneetown Fault Zone
in Gallatin County to Mt. Carmel in Wabash County. The
easternmost faults cross into Indiana. The system is about
60 miles long and about 15 miles wide, and consists of
numerous subparallel faults that generally are en echelon.
Twelve individual faults have been named (fig. 17).
(fig.
individual faults are
up to
several miles long
and
have vertical displacements ranging up to 480 feet In the
A
about 20 feet
set of entries
3 miles
at a point
was driven across the
fault
where the throw was 20 feet to gain access to the coal west
of the fault. Since the location and size of the fault were
the fault zone (Bristol and Treworgy, 1979).
The
bottom. The displacement on
the fault, as indicated by drilling, decreased from about 80
known, mining through
Individual faults of the
cally
overlap
one another
Mt. Carmel and
Wabash Mine
(fig.
in
it
was not
difficult
18).
19).
of
Wabash Valley System
in
typi-
en echelon fashion. The
New Harmony Faults
Amax Coal Company
overlap within the
in
Wabash County
Three east-trending cross-faults were encountered
two
whose
the mine between the overlapping segments of the
large
faults.
The
north sides were
cross-faults
were normal
downthrown 6
ILLINOIS STATE
faults
to 8 feet on each fault.
GEOLOGICAL SURVEY CIRCULAR
523
CUMBERLAND
MONTGOMERY
.n
FAYETTE
riFFINGHAMl
crawford7"
*>»
''
v
r—
MADISON
i
L
v
-
J
,-y^>^
]
/
richlano
~
("Lawrence
!>
Westei
A-Cottage Grove Fault System
B-Wabash Valley Fault System ,
C-Rend Lake Fault System
(
D-Du Quoin Monocline
M0NR0E
E-Dowell Fault Zone
\
i
\
F-Centralia Fault
G-Shawneetown Fault Zone
'
H-Eagle Valley Syncline
I-Ste.
Genevieve Fault Zone
J-Fluorspar Area Fault
Complex
K-Salem Anticline
L-Cape au Gres Faulted Flexure
Crown
M-Left-lateral fault in
20
10
10
20
30
40
30
II
50
Mine
4C
km
Fault, ticks on
downthrown
Fault, direction of
side
throw not indicated
Monocline
Anticline
Syncline
Figure 14.
)
V\
Faults and related structures in southern Illinois (compiled by Janis D. Treworgy, 1979).
known from numerous exposures
underground
Considerable difficulty was encountered as mining advanced
well
through the cross-faults. Extensive grading was required
mines, and locally from closely spaced test holes drilled
to achieve a gradient compatible with the mining equipment.
by coal companies.
The
efforts of grading the entries
The Rend Lake Fault System extends northward from
and handling and disposing
of excessive amounts of gob resulted
in a loss
of production.
northern Williamson County into Jefferson County, where
it
curves toward the northwest. In the south
dies out
Rend Lake Fault System
To
The Rend Lake Fault System
(fig.
20), described in detail
by Keys and Nelson (1980), occurs
Herrin (No. 6) Coal
and where mining
is
Member
is
in
an area where the
being mined extensively
likely to continue.
The
FAULTS AND THEIR EFFECT ON MINING
fault
system
IN ILLINOIS
is
in
among
it
splits
and
the faults of the Cottage Grove System.
the north, the subsurface data indicate that the
Rend
Lake Fault System probably terminates on the flank of the
Du Quoin Monocline. The known
is
length of the fault system
about 24 miles and the width varies from roughly 100 feet
to over half a mile.
2
Figure 15.
4
6
8
10 mi
The Cottage Grove Fault System.
ILLINOIS SI AT
I
CFOLOGICAL SURVEY CIRCULAR
523
^J^*
Master
t^^"
fault, ticks
Subsidary fault, ticks on downthrown side (where known)
Igneous dike
FAULTS AND THEIR EFFECT ON MINING
on downthrown side
IN
ILLINOIS
«-
(J()
£
C
UOI)BA0|3
ILLINOIS STATE
GEOLOGICAL SURVEY CIRCULAR
523
ISGS 1979
Figure 17.
Major structures of the Wabash Valley Fault System (from Bristol and Treworgy, 1979; and
they occur in the Herrin (No. 6) Coal, and downthrown sides are indicated.
FAULTS AND THEIR EFFECT ON MINING
IN ILLINOIS
Bristol, 1975). Faults are plotted
Fault,
'+50
Figure 18.
downthrow
in feet
Drill hole, elevation
of coal
in feet
Portion of Eagle No. 2 Mine of Peabody Coal
mapped from
drill-hole data.
Mine
entries
Company
in Gallatin
were driven across the
County. Mining layout was adjusted to accommodate a
its north end, where throw diminishes.
faul
fault near
ILLINOIS STATE
GEOLOGICAL SURVEY CIRCULAR
523
1
km
-250-^
Datum
point
Datum
point cut by fault
TL--
Contour, interval 25
Fault,
downthrown
ft
side indicated
ISGS 1979
Figure 19.
Wabash County, illustrating the presence of cross faults, as observed
the overlapping area of two major fault segments of the Mt. Carmel-New Harmony
Detailed structure of the top of the Herrin (No. 6) Coal in
in
the Wabash Mine of
Fault.
Datum mean
Amax
Coal
Company
sea level (from Bristol
FAULTS AND THEIR EFFECT ON MINING
IN
in
and Treworgy, 1979).
ILLINOIS
Fault postulated
/
^
s
S
Figure 20.
Rend Lake Fault System, Du Quoin Monocline, Dowell Fault Zone,
shown in feet).
Fault, direction
of
throw unknown
Fault, ticks
on
downthrown
side
Monocline
Anticline
Centralia Fault, and related structures (throw of
ILLINOIS STATE
some
faults
GEOLOGICAL SURVEY CIRCULAR
523
Individual faults of the system are nearly
although
faults,
The
longest faults can be traced for 3 or 4 miles, but
are
much
The
shorter.
a single fault
is
45
sistent direction of
about equally divided
in
No
Old Ben Mine No. 26.
displacement
most
known displacement on
largest
feet, at
con-
evident; the throws are
is
down
direction between
to the
An
en echelon arrangement of faults
especially
Jefferson
in
is
very
County, where the
common,
strike
system curves from northerly to northwesterly.
larger faults in figure
along the
The
zone
fault
named
is
and Krausse, 1981) and
20 probably consist of
of the
Many
of the
several closely
dip
the
western
the
number of
faults
example,
Old Ben Mine No. 26,
and the smaller
their displacement.
a single fault
fractures of insignificant displacement.
For
with 45 feet
Extensive grading
of belt and track entries was required to cross the fault.
system
is
northward
in
Old Ben Mine No. 21, the fault
approximately half
a
mile wide and includes
dozens of faults having displacements ranging from
inches to a
maximum
a
few
Mine No. 21, but extra measures of roof control were
needed to support the fractured rock.
Projecting the
is
Rend Lake Fault System
relatively easy because the
fairly straight.
system
Locating individual faults by
into
is
unmined
narrow and
drilling,
however,
can be difficult because of the generally small displacements.
block
feet.
in Sec.
10,
W., but they are small enough to be difficult
1
Centralia Fault
is
known from exposures
in
underin
Marion County. Like the Dowell Fault Zone, the Centralia
Fault strikes northward and follows the eastern flank of
Du Quoin Monocline. The
the
Centralia Fault consists of
one or more high-angle normal
whose major disThe maximum vertical
shown by data from drilling, may be as much
down
placements are
separation, as
as
faults
to the west.
200 feet (Brownfield, 1954).
Keys and Nelson (1980) mapped
a
fault directly in
with the Centralia Fault but farther south,
line
R.
data from
200
feet
County. This
Jefferson
E.,
1
to the west
Member (which
Herrin Coal).
A
and Centralia Fault
fault,
as
in T.
3
S.,
indicated by
holes, has a displacement of approximately
drill
down
(Smith and
Fault Zone,
Along most of the
is
lies
in
the Shoal Creek Limestone
approximately 350 feet above the
The Herrin Coal
is
having been replaced by'sandstone
Du Quoin Monocline, Dowell
in several
by Fisher
ground mines and from subsurface data near Centralia,
of 10 feet. Little grading was necessary
in
areas
The
the greater the
of throw was encountered, accompanied by only a few
In contrast,
as first described
not been traced north of the mined-out area
to detect by drilling.
in
known from exposures
downthrown opposite the
of the Du Quoin Monocline; however, on some of
faults the eastern block is downthrown. The faults have
faults
scale.
is,
in
Counties.
(1925). This fault zone consists of high-angle normal faults
T. 6 S., R.
wider the fault system
Perry
for the village of Dowell (Nelson
is
abandoned underground mines,
spaced staggered faults that cannot be distinguished at this
In general, the
lies
Du Quoin Monocline
and southeastern
Jackson
northeastern
of faults that
a series
is
flank of the
eastern
with displacements of up to 40
and down to the west.
east
The Dowell Fault Zone
normal
all
reverse faults have been noted.
few small
a
Stall,
absent at this location,
in
the Walshville channel
1975).
series of small faults has
Orient No. 3 Mine
in Sec.
been encountered
33, T. 3
S.,
R.
1
E.,
in
the
Jefferson
The Du Quoin Monocline, the Dowell Fault Zone, and the
Centralia Fault (fig. 20) extend northward from northeastern
Jackson County as far as southwestern Marion County.
branch of the Du Quoin Monocline.
The small faults strike N 15° to 35° E, roughly parallel
These three structures are closely related to each other,
with the contours of the monocline. All are high-angle
and for the purposes of
a
this report
they are regarded as
continuous structural entity.
about 2 to 3 percent; only locally does
underground mines
in
normal faults that
it
larger faults will
southeastern Perry County
In
tically related
unmined
FAULTS AND THEIR EFFECT ON MINING
IN
ILLINOIS
high-angle
normal
1
faults
have
been
along the
monocline.
can be expected along a continuous
to Centralia.
lie
close association of
monocline indicates that the two are gene-
and suggests that similar
areas
The main zone of
faults exist in the
Specifically, faults
line
faulting
from Du Quoin
would probably
near the foot of the monocline and the major displace-
ments would be down to the west. Similarly,
also
faults
may
occur along the northeast-trending segment of the
monocline
the Salem Anticline (Keys and Nelson, 1980).
than
faults signals that possibly
Du Quoin Monocline. The
The monocline, as mapped in the Herrin Coal, splits
into two branches near the southeastern corner of Washington County. The western branch continues due northward and gradually dissipates in western Marion County
near Sandoval. The eastern segment strikes northeastward,
heading and bears toward
(less
be found elsewhere along this northeast-
summary,
coal.
northerly
each other or are staggered
encountered wherever coal has been mined along the east
faults with the
a
parallel to
trending branch of the monocline.
exceed 5 percent.
flank of the
to
lie
However, the presence of these
apparently experienced no difficulties from the dip of the
returns
being mined along the
foot) that miners did not even notice the faults initially.
formerly operated on the flank of the monocline and
then
is
northeast-trending
en echelon. Their displacements are so small
The Du Quoin Monocline is a large steplike flexure
whose eastern side is downdropped. The Herrin Coal
drops as much as 300 feet within a mile across the monocline. The average gradient on the east-dipping flank is
Several
County, where, the Herrin Coal
in Jefferson
County, and northward toward Salem.
25
The Shawneetown Fault Zone
Although the Shawneetown Fault has not yet been encountered in coal mining operations, the fault zone is described
here because of
its
and some have displacements of more than 100
seam is thrust over itself and in
mines,
Locally, the coal
feet.
importance
in
effect doubled in the pit
seam was
The
the structural framework
other structures
zone strikes westward for about
they are not tectonic
Illinois (fig. 21).
where
Saline County,
15 miles into eastern
turns abruptly toward the south-
The Shawneetown has the
west.
any known
fault
it
zone
fault
in
largest
zone are downthrown more than 1000 feet
and displacement of individual faults may be
3500
zone
and
feet (Cote, Reinertsen,
Shawnee
scarp of the
as great as
Killey, 1969).
The
Hills.
The
fault
lower Pennsyl-
resistant
vanian sandstones and Mississippian limestones south of the
zone
fault
rise
not certain. They are
is
Pennsylvanian channel-fill sandstone
a
on the highwall and must have formed during Pennsylvanian
time soon after the Herrin Coal was deposited. Probably
slumping of partially
but rather are the result of
faults,
sediments.
lithified
Faults in southeastern Saline
County
in places,
prominently expressed at the surface by the northern
is
Eagle Valley
in
eroded at the base of
displacement of
the strata north of the
Illinois;
were present.
faults
of these faults and their relationship to
origin
The Shawneetown Fault Zone
known as the Rough Creek
Fault System in western Kentucky. From a point just
south of Old Shawneetown in Gallatin County, the fault
of southern
joins a major system of faults
one instance, the coal
In
(fig. 9).
where two thrust
tripled
above the more easily eroded middle Penn-
sylvanian shales north of the fault zone.
A
number of northeast-trending
in
strip
mines
been observed
faults have
southeastern Saline County, mainly
in
T. 10 S., R. 6 E. Little
known
is
of their extent and
in
distri-
bution because there are few exposures. The faults are highangle normal faults that display
on many of the
may
faults
little
drag. Displacements
exceed 50 feet and
100 feet or more. About
reach
some
in
cases
half of the faults
dip to the northwest and the other half dip to the southeast.
The
Faults in the Eagle Valley Syncline
mapped
best
line of faulting crosses
Mine (Brown Brothers Excavating)
The Eagle Valley Syncline
of
the
Fault
coal-bearing
Zone
Gallatin
in
of
the
(fig.
21).
south
County
extends into western Kentucky, where
Moorman
Syncline.
Illinois
In
miles long and 6 miles wide at
coal seams have been
mined
downwarp
Shawneetown
The structure
an east-trending
is
strata
in
it
is
the syncline
known
is
as the
roughly 15
T. 10
McCormick
A
several
underground mines
in
ground coal has been mined, mainly
consist
of
mapped
have been
in
the fluorspar-mining district imme-
diately south of the Eagle Valley Syncline.
these faults, the Grindstaff Fault
(fig.
ward into the syncline. As shown
in
Butts (1925), the Grindstaff Fault
and follows
bundles
(thrust) faults.
northeast-trending faults of large displacement
is
At
least
one of
21), extends north-
more than
few
a
detrimental
difficult
The
of
show
several cases
no attempt
slicken-
almost 7 miles long
for large masses of roof rock. These problems are often
compounded by
the water entering along the fractured
tered during mining.
which
zones,
drilling,
softens
the
shales.
faults,
Because of the small
they cannot be projected by
and are not always recognized even when encoun-
of faults has been encountered recently in
surface (strip)
mines of Peabody Coal Company,
northern part of T. 10
S.,
in
the
R. 8 E., Gallatin County.
The
trend generally east-west and dip at shallow angles
that are usually less than 45°.
the most
in
was made to mine through them. The low-angle
in detail.
horizontal
reverse
They have created such
stability.
roof conditions that
displacements of the
faults
these mines
feet of heave, but these faults are highly
downthrown as much as
100 feet in places. Butts also mapped several smaller
northeast-trending faults, but he did not show these faults
series
in
low-angle
coal and associated strata seldom
roof
to
north-trending,
sided surfaces of these faults create easy planes of separation
Strata southeast of the fault are
A
mapped from
map compiled by
a
heading of N 25°E across the entire syncline.
a
in
southern Saline and south-
Williamson Counties. The faults
Many
1
with the
different style of faulting has been encountered in
eastern
(No. 5) Coal.
in line
Fault, a large fault that has been
Most mining has been by surface methods, but some underthe Springfield
and 30,
Counties.
the Eagle Valley Syncline.
in
Track
J. J.
surface exposures to the southwest in Johnson and Pope
broadest point. Several
its
21) These faults are directly
(fig.
the
19, 20,
and the Jader Fuel Co. Mine No.
R. 6 E.,
S.,
Sec. 10
in Sec.
(e.g.,
Some
of the faults are nearly
bedding-plane faults). Normal faults are
common
type of faults here; they have throws
Other tectonic faults
in Illinois
Because of the degree of control available from
borings
in
most of
Illinois,
it
oil-test
seems unlikely that any
fault
systems of the magnitude of the Wabash Valley or Cottage
Grove Fault Systems
still
remain undiscovered. Nevertheless,
ranging from 10 to 30 feet or more. These normal faults
many
smaller tectonic faults probably exist in the Illinois
usually too deep for
Basin,
and may be encountered
hinder
mining because the coal
is
economic recovery on the downthrown
(low-angle
reverse
faults)
are
also
side.
present
Thrust faults
in
the strip
A number
faults have
of
been observed
ILLINOIS STATT
in
future mining operations.
northwest-trending
in
high-angle
underground mines
in
normal
Christian,
GIOLOGICAL SURVEY CIRCULAR
523
FAULTS AND THEIR EFFECT ON MINING
IN
ILLINOIS
Macoupin, Montgomery, and Sangamon Counties of central
The
Illinois.
faults are very straight along strike
One such
both northeasterly and southwesterly dips.
in
Christian
County extends
mines and shows
(No. 6)
much
as
as
through two
15 feet of throw
in
Mine of
drilling
Crown
Freeman United Coal Mining Company, in
Macoupin County, has as much as 7 feet of
Another
high-resolution seismic surveys.
II
the Herrin
beyond the
and by
fault
mined-out area has been confirmed both by
northeastern
fault
at least 6 miles
The continuation of the
Coal.
and show
throw and continues
fault in the
for 3,000 feet; neither end has been
found. Similar faults of smaller displacement were
mapped
Crown Mine, about 5 miles east of Crown II Mine
Montgomery County. Yet another northwest-trending
normal fault was reported by Simon and Harrison (ISGS,
unpublished field notes) in the Farrand Coal Company's
mine on the east side of Springfield, Sangamon County.
The coal was downthrown 14 feet to the southwest along
at the
I
in
Crown
and are about 5 miles to the
II
imply that the fault
and thus
is
at least 7 miles long.
is
Although the fault
most
small vertical offset in
II
is
fairly long
coal
and has
seam shows only
places. Perhaps other faults
been encountered
have
nature
this
Crown
in
on mining, the
significant effects
of
These facts
east.
continuous between the two mines,
underground
in
workings and were not recognized.
may
Possibly, faults
exist in
Basin. Faults are likely to be
unmined
found
areas of the Illinois
with any
in association
of the large folds (anticlines and synclines)
in
the basin.
We
have already noted the occurrence of faults along the
Du Quoin Monocline. Other
may
structures that
have
associated faults include the La Salle and Clay City Anti-
and the Salem and Louden Anticlines
clinal Belts,
23).
(fig.
NONTECTONIC FAULTS
OF ILLINOIS
IN
Tectonic faults
and elsewhere are confined to
COAL-BEARING STRATA
this fault.
The presence of
so
many
similar faults over so large a
Illinois
in
region indicates that the faults are the product of regional
well-defined zones or systems, and often can be
tectonic stresses; however, the overall distribution of the
with
and their relationship to the regional structure have
faults
not yet been determined.
A
Gartner (ISGS, unpublished
Company mine
was reported by Eadie and
field notes) at
the
Eddy Coal
north of Springfield. The notes describe
zone trending north-south and dipping 60° to the
a faulted
west. Eadie and Gartner wrote that the fault had 12 to 18
how
inches of strike-slip displacement;
is
not mentioned. Faults of
occur frequently on the west
were randomly distributed.
The
fault
this
Illinois
they determined this
type were reported to
mine and apparently
side of the
of
a
small tectonic
the zone of strike-slip faulting
is
Crown
mine of Freeman United
Coal Mining Company (fig. 22). The coal in this mine is
flat lying, and the strike-slip fault shows left-lateral displacement. It runs east-west and shows a maximum dip-slip
of about 4 feet. The strike-slip, as indicated by the offrecently identified in the
to
70
about
II
Innumerable
feet.
northeast-trending
extensional fractures, which tend to increase in
and intensity toward the
fault,
These fractures cause
bility
and admit water into the mine. Thus
local
problems of roof
direction
of
is
much
smaller
displacement
This fault at
Crown
for about 2 miles, but
II
its
in scale
(Nelson
has been
the
insta-
this fault has a
structure similar to that of the Cottage Grove Fault
15), but
free of
rocks
makes them
faults
distribution
their
Crown
fractures in
Crown
I
II
is
ISGS has become
area, and,
actively involved in
mapping nontectonic
underground mines and learning their geologic
in
of this
Results
affinities.
Krausse et
aration),
al.
work have been presented by
(1979), Krausse and Damberger
(in
prep-
and Nelson and Ledvina (1979).
Nontectonic faults can be divided into
categories,
origin.
in
on a small scale,
often highly dependent upon local
seam or roof rock. In recent years the
by
a
number of
based on their form and presumed modes of
These include compactional
and gravitational slumps and
faults, clay-dike faults,
slides.
Compactional faults
System
Most sediments undergo considerable compaction as they
changed into rock, and different sediments compact at
are
widely varying rates and amounts. Plant matter that becomes
coal
is
assumed to undergo
thickness during
and
percent or more of their volume
Nance,
1980).
mapped along
strike
termination at either end has not
was encountered
directly
on
at least a tenfold reduction in
and has the opposite
in
now abandoned Crown
lie
is
variations in the coal
line
the extreme
I
Mine. The
with the fault
in
coalification.
Muds commonly lose 50
when they become shale;
on the other hand, well-sorted sand undergoes
little
com-
paction. Apparently, therefore, any irregularities in a sedi-
mentary sequence
in
and probably no mine
and lack of continuity of these
difficult or impossible to detect during
Illinois are closely restricted
and these
fault
size
not random. Various types of nontectonic faults
are
been found. According to ISGS unpublished mine notes,
northern part of the
Illinois,
exploration; nevertheless, their occurrence and distribution
an area of intense fracturing similar to that observed along
the
of
them. The small
number
are associated with
fault.
(fig.
nontectonic faults are present throughout the
above the coal, varies from about
setting of lenses of shale
15
In contrast,
faults
documented example
best
central
in
degree of confidence before mining begins.
coal-bearing
different type of fault
mapped
fair
a
will
stresses
produce
stresses during
are often relieved
compaction,
by the development
of compactional faults.
Small
compactional
faults are
mine and are known to miners
ILLINOIS STATE
encountered
as "slips." Slips
in
every
may
GEOLOGICAL SURVEY CIRCULAR
have
523
FAULTS AND THEIR EFFECT ON MINING
IN
ILLINOIS
Figure 23.
Geologic structures of
Illinois
(compiled by Janis D. Treworgy, 1979).
ILLINOIS STATE
GEOLOGICAL SURVEY CIRCULAR
523
no apparent displacement but are well-known
or
little
lithology.
Channel sandstones above the coal are commonly
where the immediate
hazards because their slickensided surfaces allow separation
accompanied by
of pieces of roof.
roof changes from shale to limestone, or from gray shale
The presence of compactional
often can
faults
to black
be
fissile
related to an irregularity in the coal or the overlying rocks;
parallel to the
for example, the large concretions in black shale are usually
Mapping the
surrounded by
a set of faults (fig. 24).
composed
hard
of
siderite—that grew
rock-usually
in
was compacted into
this
mud
hard body, the
partially
before
common
Another
which
a coal
One
of the best clues
top coal or on the
vertical
extensional
calcite,
pyrite,
sandstone (Krausse et
shale, siltstone, or
presence.
is
by gray
are overlain
rib.
A
is
a
goat beard
fractures that
or other minerals
"goat beard"
is
is
(fig.
a
in
the
bundle of small
usually
26).
filled
with
Goat beards
many compactional
occur at the lower ends of
1979), were
al.,
by the
however, can be detected
faults,
seam. Rolls, which are
where coal seams
areas
the "hidden slip,"
is
penetrates the roof but not the coal.
careful observer because there are clues that indicate their
which are protusions of sediment
from the roof into the top of
in
faults
and thicknesses of the roof strata
danger to miners
a fault that
is
Many hidden
yielded partially by folding and
for compactional
lithologies
facilitate projecting the locations of faults a short dis-
A common
it
As the mud compacted around
setting
25),
(fig.
Faults in such areas normally strike
shale.
boundaries between the two types of rock.
tance ahead of the working face.
or
pyrite,
mud
by slippage around the edges of the concretion.
within "rolls"
common
limestone,
place within the black
shale.
may
Concretions are
faults, as are areas
faults,
formed before the coal and surrounding sediments were
fully lithified. During compaction the peat was deformed
clay-dike faults, and other normal faults. Another clue to
around the lens-shaped body of sediment
coal.
same manner
Many
as black shale
the
deformed around
a
roll, in
a
the
up to 3
roll,
more of throw. The
are likely to be. The
feet or
the larger the faults
usually dip
away from the center of the
bute to roof
falls
(Krausse et
Compactional
al.,
roll
and
faults are likely to be
Cleat
is
an abrupt deviation of cleat
is
in
in
fault
fre-
interrupted near faults or
is
mine openings can be
to the detection of faults.
contri-
the top
the coal.
Leaving top coal
faults
in
normally straight and continuous, but
other irregularities
larger
Top
and the condition (such
a
hindrance
coal can conceal both the
as a
change
in
the type of
rock forming the roof) that led to the formation of the
1979).
the rocks above the coal change abruptly
hidden fault
quently becomes curved or
concretion.
of the faults associated with rolls are large: hundreds
of feet long with
the
is
in
found wherever
in
fault.
thickness or
Herrm (No. 6) Coal
Figure 24.
Concretion
in
black shale above the Herrin (No. 6) Coal.
concretion grew and solidified before the shale was
allowed
it
to separate
from the
roof.
FAULTS AND THEIR EFFECT ON MINING
IN
ILLINOIS
The
lithified.
around the concretion, indicating that the
formed around the edges of the concretion and
layers of shale are bent
Compactional
slips
Body
of roll
Normal
fault (extensional
and compactional)
Gray shale roof
Herrin (No. 6) Coal
Figure 25.
roll (from Krausse et al., 1979), showing a fault that formed as a result of differential compaction of shale and
and the coal "riders" form intersecting planes of weakness in the roof, which may cause the body of the roll to fall.
Sketch of a typical
coal.
The
fault
Figure 26.
Mineralized "goat beards" at the lower end of a fault
in
the Herrin (No. 6) Coal. Scale at
left is
10
cm
(about
4 inches).
ILLINOIS STATE
GEOLOGICAL SURVEY CIRCULAR
523
cases the ruptures
Clay-dike faults
formed were
vertical or nearly vertical,
and continued stretching pulled the walls of these fissures
Clay-dike
faults,
named by Krausse
first
et
(1979),
al.
are closely associated with clay dikes. Clay dikes are not
faults
in
the
proper sense of the word, but they bear
mention because of
their relationship with clay-dike faults.
Clay dikes, also called
"horsebacks" or clay veins, are
or inclined intrusions of clay
irregular vertical
seams and adjacent rocks
width from
from
a
few
less
(figs.
27 and 28). They range
than an inch to several feet, and
many hundreds
feet to
into coal
Some
of feet.
in
in
length
penetrate
away from each
to
other. Clay
from above the seam moved
the fissures, and clay dikes were formed
fill
Other fractures
in
(fig.
in
29).
the coal-forming material were not ver-
but inclined. The walls of these fractures were not
tical,
pulled
away from each
other,
intrude along the fractures.
so
little
or no clay could
as the
Instead,
coal-forming
material continued to be stretched, the walls of the inclined
ruptures remained
in
contact with each other and slippage
occurred, creating clay-dike faults
the entire coal seam, whereas others affect only the upper
(fig.
29).
clay-dike faults are normal faults. Most clay-dike
All
maximum
and lower layers of the roof. Where they are
numerous or both, clay dikes adversely affect
roof stability and contribute large amounts of rock to the
faults are small, with less than 2 feet of
coal mined.
clay-dike faults with 2 to 4 feet of throw are also numerous;
layers of coal
large
or
Clay dikes and clay-dike faults were formed by horizontal
stretching
of
the sedimentary layers before they
were hardened to rock and
forces
is
delve into this here.)
led
to
coal.
(What caused the stretching
being debated by geologists, and
The extensional
we
Clay dike
in
not
stresses eventually
rupturing of the coal-forming material.
Figure 27.
shall
the Springfield (No. 5) Coal
in a
In
some
surface mine.
Most of these small
faults affect only the
of the coal seam and the lower layers of the roof. Larger
most of these penetrate the
as
well
faults,
coal
entire thickness of the coal
some layers of the roof and floor. Still larger
some of which offset the entire thickness of the
as
seam, are occasionally
encountered.
Figure 28.
Vertical clay dike in black shale
in
above the Springfield
an underground mine. The V-shaped
of intersecting slips above the clay dike seriously
weakened the roof and contributed
location.
ILLINOIS
al.
ment, but this was exceptional.
set
IN
Krausse et
(1979) reported a clay-dike fault with 18 feet of displace-
(No. 5) Coal
FAULTS AND THEIR EFFECT ON MINING
throw.
upper portions
to the
fall
at this
With most clay-dike
Pressure of overburden
1
of throw, the
1
maximum
faults that have less
offset
of the coal with the roof
_~_ :ciay
~-~L ~ Cr^"- ~ - ~-"~ -T -~~~~Z_
(shale)
1
c
^Bfl^H
~*"
.2
|H' ,9H
Coal-forming
|
material
^
Underclay
"
floor.
75
c
that
c
of the fault
roughly 35° to 55°.
is,
many
In
cases the upper portion
i
0)
—
and
Clay-dike faults typically have moderate angles of dip-
H
>-
LU
30). Larger clay-dike faults
appear to maintain their throw through the roof, coal,
e
ra
(fig.
than 3 or 4 feet
observed near the contact
is
in
the roof flattens and
following bedding planes
— _ ""' "- — — — — —
-
in
may become
the roof
(fig.
LU
horizontal,
The lower
30).
portions of the smaller faults steepen toward the vertical,
and the faults die out amid
a set
of "goat beards"
(fig.
26).
Clay-dike faults with more than 2 or 3 feet of offset generally
do not display
this curvature along dip; rather,
they
tend to be planar and to dip consistently at35°to 55°. This
moderate angle of dip distinguishes them from tectonic
normal faults, most of which dip at 60° or greater.
A common
~—~—
Clay (shale)"
X~-^^^ x ^^
"false
feature of clay-dike faults
drag," which
is
illustrated
faults in figure 30. False drag
H Coal-forming
1
are
^R^^H ^^^^iKn^MM
is
the so-called
on the two right-hand
means the beds near the
so that the layers tend to
fault surface
(compare
figs.
become perpendicular with the
9 and 30). False drag has the
effect of increasing the apparent
throw of the
fault.
may
that are offset several feet at the fault surface
—
~"X__
—
— Underclay
nearly the
ISGS 1981
changes
in
Geologists
Underclay
Figure 30.
Origin of clay dikes (A) and clay-dike faults (B).
>< ?< .x
common;
at
away from
are traced
elevation of beds on opposite sides of the faults.
have
not
reached
why some
agreement on
clay-dike faults have false drag.
>< *< ><
Clay -dike faults. Fault surfaces are curved and typically almost horizontal
at the base.
same elevation when they
Beds
lie
the fault. In contrast, tectonic normal faults produce real
B
Figure 29.
fault
bent opposite the direction of apparent movement,
in
the roof; they steepen
downward, and become
Extension fractures (goat beards) are found at bases of faults (A) and also above some faults
layers tend to be folded perpendicular to the fault surface. Convergent bedding (D) in coal
angle fractures branching off the main fault. Shale on hanging wall (E)
is
thicker than shale
ILLINOIS STATE
(B). False
may accompany
on footwall, and
its
bedding
is
vertical
drag (C)
is
small, low-
disturbed.
GEOLOGICAL SURVEY CIRCULAR
523
Detailed mapping of clay-dike faults
many
underground
in
them can be traced
hundreds or even thousands of feet along strike. They
coal mines has disclosed that
for
may occur
linear,
parallel
in
or swarms, but they are not
tectonic faults.
are
as
sets
may form
plotted on a map.
when
patterns
they tend to be
Instead,
strongly curved along strike, and
reported that clay-dike faults,
Gravitational slumps and slides
of
roughly circular
Krausse et
(1979)
al.
when mapped, commonly
Some
on the sediments before they were
slumps, landslides (above or below water), and
mud
Layers of
can
flow
coal seams,
may
or
may
no
faults with
An example
found between
severe instability
is
The same
Mine, described
in
may have no
one
clay at
filling
foot or more
1
Most clay-dike
changes
fault
place, a thin filling of clay at
another place, and elsewhere
with a
dikes.
may
turn into a clay dike
faults are
not large enough to force
the layout of mines, but where the faults are
in
numerous, it becomes difficult to avoid mining large
amounts of rock from the roof or floor. To this rock is
added the clay from fillings along the faults and from clay
Like
dikes.
roof stability
underground mines. Areas where
in
intersect can
faults
clay-dike faults tend to lessen the
faults,
all
several
be especially troublesome. Clay-dike
do not appear to be responsible, however,
ducing water or gas into mine workings in Illinois.
faults
in
New
2),
Colchester
Burnside,
(No.
Springfield
(No. 5),
Herrin (No. 6), and Danville (No. 7) Coal Members. Those
in
the Springfield and Herrin Coals
in central
and western
have been studied the most thoroughly.
Illinois
Clay dikes are most abundant
in
the Springfield (No. 5)
Coal from Sangamon, Logan, and Menard Counties north-
ward
and Peoria Counties. Damberger (1970,
into Fulton
1973) reported that nearly vertical clay dikes ranging from
a
few inches to about
a foot
area. Inclined clay dikes
to occur rarely
underground
in
mines
wide are most typical of
and clay-dike
faults
the Springfield Coal.
of
appears
mining.
Sangamon and Logan Counties,
cores drilled
in
Evidence of clay dikes frequently
in
these
two
and Peoria Counties, where the coal
there
enough clay dikes to add
are
waste separated
in
being strip mined,
significantly
to the
from
the Herrin
in
(No. 6) Coal.
They
are
common
County northward to Macoupin and Montgomery Counties, and also are found in Vermilion County
and
St. Clair
in
Field.
the northwestern region of the
They
Monocline,
Illinois
Basin Coal
are rare or absent in mines east of the
in
Du Quoin
the deeper portion of the Illinois Basin.
The
factors that control the distribution of clay-dike faults in
Illinois are
(1979) and
an area
is
(figs.
in
31 and 32).
a series of faults
is
body and dip gently
that are horizontal in the center of the
inward around the margins. These faults locally
at the
lie
top of the coal but were not observed to penetrate the coal.
The
body
shale and siltstone in the shear
sheared
in a
manner that
Roof control within the shear body
of the
many
crumpled and
is
indicates sliding of soft sediments.
very difficult because
is
slickensided surfaces within and below
Additional
bodies
shear
related to the
sand
is
the
at
may
be
loading of soft, rapidly deposited, water-
At the Orient No. 6 Mine, sandstone
saturated sediments.
overlies
it.
mapped
been
have
20 feet or more of shale above the coal. Since
denser than mud, a top-heavy situation was created.
The sand may have slumped downward toward the coal as
the mud and clay moved outward and upward to displace
the sand (Nelson and Ledvina, 1979). Shear bodies
common
The
coal.
may be
features where thick shale and sandstone overlie
distorted and slickensided rock of a shear
should be easy to recognize
body
in a core.
RECOMMENDATIONS
The following
are suggestions and
recommendations aimed
primarily at operators of underground mines, but also
be of value to operators of surface mines
Faults
1.
and
other
be
should
data about
all
may
faulted areas.
anomolies
geologic
studied attentively and mapped, and
should
in
be
them
recorded carefully. Faults and other features
can be plotted directly onto mine maps as they are updated.
preparation plants.
Clay-dike faults, as well as clay dikes, are widely distributed
deformed
intensely
is
The lower boundary of the shear body
counties. In Fulton
is
al.
some of the
however, clay dikes were numerous enough to seriously
interfere with
et
Ledvina (1979). The shear body
Nelson and
No. 6
at the Orient
by Krausse
detail
this
were reported
In
body"
the "shear
Orient No. 6 Mine. The origin of the shear bodies
including the
Illinois,
the rock above
in
about 1,800 feet long and several hundred feet wide
for intro-
Clay-dike faults and clay dikes have been observed in
most of the minable coal seams
common
of a gravitational structure that caused
which the roof rock
width.
in
quite
is
and can contribute to unstable roof conditions.
not contain clay along the
and true clay
clay,
flows.
or intrude the adjacent strata. Gravi-
laterally
trasting types of rock in the roof.
mud
or clay, under the pressure of overburden,
deformation
tational
Clay-dike faults
lithified.
Sediments deposited on sloping surfaces are subject to
follow or run parallel with the boundaries between con-
fault surface. All degrees of transition are
caused by the effects
faults in coal-bearing strata are
of gravity
not known.
FAULTS AND THEIR EFFECT ON MINING
For every
should be recorded.
ILLINOIS
I
be plotted, even
if
its
a
amount of apparent
(e.g.,
recommend
continuous for more than
normal, reverse)
that any fault that
is
couple of hundred feet should
displacement
is
slight. In
many
cases
mine
becomes large enough elsewhere to disrupt production.
Mapmakers should be cautious about projecting faults as
a
fault
single
IN
fault, the direction of dip, the
displacement, and the type of fault
that
seems insignificant
straight or curved
lines.
in
one part of
Nearly
all
a
large faults
in
35
a
e
Ml
Major roof
fall
^3®i
Minor roof
fall
«•—-*
Kink zone
.
•
in
Well-bedded dark-gray shale,
lower portion of Energy Shale
u]_Lllli. Fault and shear plane— low angle
u
roof
Rib rashing
uuilli^- Multiple major shear planes withir
|| Poorly bedded medium-gray shale,
upper portion of Energy Shale
shear
—
Intensely sheared area with dense
Boundary between rock
body
spacing of numerous small shear
units
planes
Crib
Boundary of shear body
Direction of striations
Timber props
Figure 31
jjxuii
'
i'i
nu Fault and shear plane— high angle
Portion of the Orient No. 6 Mine showing outline of the shear body (heavy dashed
.
line).
The shear body
is
a
zone of intensively
disturbed rock in the roof. Roof failures (dark gray) are numerous under the shear body.
Illinois are
composed of multiple
breaks,
commonly arranged
en echelon.
2.
All
people
3.
data relating to faults on or near a coal pro-
perty should be compiled. Sources of data include logs of
maps
of mines, published reports and manuscripts,
drill
holes,
files
of agencies such as the ISGS, and the recollections of
who worked
in
Companies
should
nearby mines.
keep abreast of the current
technology for locating and predicting faults and other
interruptions in coal seams.
made
in
Many developments
are being
the application of seismic and other geophysical
methods of exploration.
ILLINOIS STATE
GEOLOGICAL SURVEY CIRCULAR
523
20- -60
Figure 32.
North-south cross section through the shear body at the Orient No. 6 Mine, illustrating Nelson and Ledvina's theory of the shear
body's origin (1979). Thick sand was deposited rapidly above medium- and dark-gray mud. The sand was denser than the mud, and
became unstable. The sand may have pressed downward on the mud so that the mud squeezed outward and
movement of sediments may have been responsible for the intensive faulting and disturbance observed in the shear body.
the pile of sediments
upward.. This
Mining plans should
4.
with irregularities
changes
in
in
be flexible enough to cope
the coal seam and
sizes or shapes of pillars
the roof. Simple
can be beneficial
reducing roof failures caused by faults.
altering the orientations of entries
in
On
a
in
larger scale,
and panels may improve
efficiency and safety in faulted areas.
5.
When
faults
are
encountered
possible courses of action should be explored.
large
little
blocks of coal
difficulty are
that
could
have
abandoned simply because the operator
did not understand the nature of faults. Many,
lines
Sometimes
been mined with
if
not most,
of faulting have gaps across which mine entries can be
driven. Operators should actively seek these gaps, using
unexpectedly,
FAULTS AND THEIR EFFECT ON MINING
IN
ILLINOIS
all
the exploratory methods at their
all
command.
37
REFERENCES
M.
Billings,
1954, Structural geology: Prentice-Hall,
P.,
514
edition,
Inc.,
2nd
Krausse, H.-F., and H. H. Damberger, Clay-dike faults and associated
structures in coal-bearing strata— deformation during diagenesis:
p.
Compte Rendu, Ninth
Bristol, H. M.,
System
in
and
D. Treworgy, 1979,
J.
southeastern
Illinois:
The Wabash Valley Fault
Illinois
International Congress of Carboniferous
Geology and Stratigraphy,
in press.
State Geological Survey,
Krausse, H.-F., H. H. Damberger, W.
Circular 509, 20 p.
J.
Nelson, S. R. Hunt, C. T.
Ledvina, C. G. Treworgy, and W. A. White, 1979, Roof strata
Brownfield, R. L, 1954, Structural history of the Centralia area:
Geological
State
Illinois
172,31
Survey,
Report
of
Investigations
a
Herrin
summary
(No. 6) Coal and associated rock
report:
State Geological
Illinois
in
Illinois—
Survey,
Illinois
Mineral Notes 72.
p.
Geology and mineral resources of the Equality(parts of Gallatin and Saline Counties):
State Geological Survey, Bulletin 47, 76 p.
Butts, Charles, 1925,
Shawneetown
Illinois
of the
area
Lepper, C. M., and F. Ruskey, 1976, High-resolution seismic reflec-
techniques for mapping coal seams from the surface:
tion
Mine Health and Safety Program,
U.S. Bureau of Mines, Coal
Technical Progress Report 101, 17 p.
1955, Metamorphism of coal by peridotite dikes in
southern Illinois: Illinois State Geological Survey, Report
K.
Clegg,
E.,
of Investigations 178, 18 p.
Nelson, W.
and H.-F. Krausse, 1981, The Cottage Grove Fault
J.,
System
southern
in
Illinois:
State Geological Survey,
Illinois
Circular 522.
Clegg, K. E., and
and
Illinois
C. Bradbury, 1956, Igneous intrusive rocks in
J.
their
economic
significance: Illinois State Geological
Survey, Report of Investigations 197, 19
Nelson, W.
J.,
and
A
C. T. Ledvina,
gravitational slide in the Energy
Member overlying the Herrin (No. 6) Coal in southern
Compte Rendu, Ninth International Congress of
Shale
p.
Illinois:
L Chapman, and D. E. Dunster, 1979,
methods applied to coal-mining problems:
Paper presented at AAPG annual convention, Houston, TX,
Coon,
Reed, W.
B., J. T.
J.
Surface
Carboniferous Stratigraphy and Geology,
April 1-4, 1979.
Nelson, W.
J.,
E.,
guide
D.
Reinertsen, and M. M. Killey, 1969, Field trip
L.
1969
leaflet
A
and
F,
Equality
Area:
Illinois
E.,
1979, High-resolution seismic methods in coal exploAAPG annual convention, Houston,
ration: Paper presented at
April 1-4,1979.
S.,
Herrin
Serres,
Y.,
seismic
1970, Clastic dikes and related impurities
H.,
(No. 6) and Springfield (No. 5) Coals of the
Nance, 1980, Geologic mapping of roof
Mine, Macoupin County,
Illinois
State
Illinois:
Geological
SME-
Survey,
p.
in
Illinois
1978, Coal mine ground control: John Wiley
450
&
Sons,
p.
and C. Wiles, 1977, Mini-Sosie: New high resolution
reflection system for coal and mineral exploration,
engineering, hydrology, geothermal, and shallow petro-
civil
Damberger, H.
B.
II
80-308;
Reprint 1981-A, 8
Peng, S.
Inc.,
TX,
Crown
Preprint,
State
Geological Survey.
Daly, T.
and Roger
conditions.
AIME
Cote, W.
in press.
seismic
leum exploration: 79th
Mining and Metallurgy,
AGM
of the Canadian
Canada,
Ottawa,
April
Institute of
20,
1977.
Basin: in Depositional environments in parts of the Carbondale
Formation— western and northern Illinois:
logical Survey, Guidebook 8, p. 111-119.
Illinois
State Geo-
Smith, W.
H.,
and
Stall, J. B.,
coal conversion
in
1975, Coal and water resources for
Illinois:
Illinois
Cooperative Resources Report 4, 79
Damberger, H.
1973, Physical properties of the
H.,
Illinois
(No. 6) Coal before burial, as inferred from earthquake-induced
disturbances:
Compte Rendu, Seventh
International Congress
of Carboniferous Stratigraphy and Geology,
v.
2, p.
J.,
Illinois
31
McGraw-Hill Book Company, 547
&
in
Du Quoin:
N.,
1976, Coal seismic: Foreign Trade Corporation Technical
Cooperation Agency, Panska
6,
Czechoslovakia.
State Geological Survey, Report of Investigations 5,
B., Elwood Atherton, T. C. Buschbach, Charles Collinson,
John C. Frye, M. E. Hopkins, Jerry A. Lineback, and Jack A.
Simon, 1975, Handbook of Illinois stratigraphy: Illinois State
Willman, H.
Sherbon, 1963, Elements of structural geology: John Wiley
Sons,
J.
p.
341-350.
p.
Hills, E.
Keys,
1925, Structure of Herrin (No. 6) Coal near
Survey,
Spencer, E. W., 1969, Introduction to the structure of the earth:
Stas, B.,
Fisher, D.
State Geological
p.
Herrin
Inc.,
483
and W.
southern
J.
Geological Survey, Bulletin 95, 261 p.
p.
Nelson, 1980, The
Illinois:
Illinois
Rend Lake
Fault System
State Geological Survey, Circular
513, 23 p.
ILLINOIS STATE
GEOLOGICAL SURVEY CIRCULAR
523
GLOSSARY
Anticline
Bedding
An
elongate upward fold
The
the earth's crust; a structural arch. Frequently traps petroleum and natural gas.
in
and other rocks
layering along which coal, shale,
split.
Generally horizontal except where rocks have
been folded or faulted.
Bedding fault
Breccia
A
fault that follows a
Material
bedding plane.
composed of
coarse, unsorted, angular, jumbled rock fragments, held together by clay or by
cementing minerals. Often found along fault zones.
Clay dike
A
clay-filled vertical or inclined fracture in coal
and adjacent rocks. Usually very
irregular;
can be up to
several feet wide.
Clay-dike fault
A
nontectonic normal fault associated with clay dikes and believed to have been formed by the same
process as clay dikes.
Compactional fault
Dike
A
fault believed to have
as
they hardened into rock.
Any
formed
as a result of stresses
intrusion of foreign material
(e.g.,
caused by unequal rates of compaction
sediments
in
which cuts across the
clay, sand, igneous rock) along a fracture,
bedding and layered rocks.
Dip
The
pitch or inclination (measured
in
degrees from the horizontal) of any surface, such as a bedding
plane or a fault plane. Horizontal surfaces have 0° dip, and vertical surfaces dip at 90°.
Dip
slip
The component
of displacement
on
a fault parallel
with the dip of the fault surface.
Dip-slip fault
A
fault
Displacement
A
term loosely used to refer to the amount of offset on
throw or the dip slip.
on which the principal motion was dip
slip
(up and down).
a fault.
May be
equal to the net
slip,
but often
indicates only the
Dome
An upward-bulging
fold in the earth's crust,
except that the anticline
Drag
is
shown
as elongate
shown as roughly
on a map.
circular
on
a
Folding or bending of rock layers adjacent to a fault, caused by friction along the fault. Strata are bent
in
the direction of movement.
A common
arrangement of
faults in
which individual
faults are parallel to but staggered or offset to
each other, so that where one fault ends another begins slightly to the right or
False drag
map. Similar to an anticline
Folding or bending of rock layers observed along some faults,
in
which the
left.
strata are
bent opposite to
the direction of motion. Causes are poorly understood.
Fault
Fault plane
Fault surface
Fault system
Fault zone
Any
A
fracture in the earth's crust along which
fault surface,
The surface
A
Goat beard
Grab en
Hanging wall
Heave
High-angle fault
essentially planar (not curved).
in a
common
zone rather than
May be
either curved or planar.
stress field.
belt of fractured, brecciated, or pulverized rock
found along
a large fault.
Most
large faults have
a single fault surface or plane.
The block of rock below an
inclined fault.
Informal term for the set of small, closely spaced, mineralized vertical fractures found near the lower end
of
Gouge
has occurred.
of the fault, along which slippage has occurred.
group of tectonic faults that formed
The
a fault
Footwall
when
movement
many
Rock
A
small faults in coal.
A
goat beard
in
the top coal often warns of the presence of a fault
that has been pulverized to a claylike consistency
block of rock dropped
The block
downward between two normal
fault
zone.
faults that face each other.
of rock above an inclined fault.
The horizontal component of movement along an
A
in a fault
whose surface dips
at
inclined dip-slip or oblique-slip fault.
an angle of 60 to 90° from the horizontal.
in
the roof.
Horseback
A
Horst
A
miner's term for any of various disturbances
Left-lateral fault
A
Monocline
Illinois
the term usually refers to clay dikes.
I
fracture in the earth's crust along which
no appreciable movement
(slip)
has occurred.
A strike-slip fault on which, to an observer straddling the fault, the left-hand block has moved toward
the observer. Or, if the observer stands on one block and looks across the fault, the opposite block has
moved from
Low-angle fault
seams. In
block of rock thrown upward between two normal faults that face away from each other. Opposite
of
Joint
in coal
A
fault
A
right to left.
whose surface dips
an angle of 0° to 30° from horizontal.
at
steplike fold or flexure in layered rocks.
Many monoclines
overlie a fault at depth; the rocks near
the surface are bent rather than broken.
Mullion
Large polished grooves or furrows along a fault surface. Mullion results from the friction of
and indicates the angle of net
Net
slip
A measurement
of the total offset of
combination of dip
Nontectonic fault
A
fault that
slip
and
formed by
is
movement
slip.
two formerly adjacent points along
a fault surface.
Net
slip
is
a
strike slip.
stresses that affect
sediments as they are being transformed into rock. Difficult
to predict.
Normal fault
A
moved downward
Oblique-slip fault
Reverse fault
A
relative to the footwall.
of
shows a combination of dip slip and strike slip. Oblique
movement, or in separate events of dip slip and strike slip.
A
fault with
fault that
Roll
Opposite of
An
to the footwall.
The
in a single
episode
The movement on
is
opposite to the move-
and
as used in this report,
a reverse fault
in
coal seams.
As used
in
Illinois,
to a generally elongate protrusion of the roof rocks onto or into a coal seam. Rolls are often
accompanied by compactional
Slickensides
may occur
left-lateral fault.
informal term for various disturbances
roll refers
slip
wall
an inclined surface, and predominantly dip-slip movement, along which the hanging wall
moved upward relative
ment on a normal fault.
has
Right-lateral fault
dip-slip movement, along which the hanging
The most common type of fault in Illinois.
and predominantly
fault with an inclined surface,
has
faults.
surface of a fault, polished and striated by the friction of
movement. Slickensides record the most
recent episode of slip on the fault.
Slice
Slip
A
narrow
sliver
or block of rock within a fault zone or between
Movement along
a fault; also
two
closely spaced parallel faults.
used as an informal term for small faults or slickensided surfaces
in
coal
or roof. Most slips are compactional faults.
Strike
The
directional heading of a fault or other geologic surface, as plotted
a direction (northeast), as degrees
measuring clockwise from
Strike slip
Strike-slip fault
Syncline
Tectonic
Tectonic fault
Throw
Thrust /a nil
Wrench
fault
The component
A
fault
An
principal
downward
motion was
strike slip (horizontal).
fold in the earth's crust; a structural trough. Opposite of anticline.
Related to or formed by deep-seated regional stresses within the earth.
A
fault that
The
vertical
is
on a map. May be expressed
formed by tectonic
component
of slip
A
reverse fault, generally
A
strike-slip fault, especially
on
stresses.
a fault.
one whose surface dips
less
as
or south (N45°E), or as degrees on a 360° compass,
due north (045°).
of displacement on a fault parallel with the strike of the fault.
on which the
elongate
away from north
than 30".
one of major proportions.