EARTHQUAKE NOTES
Eastern Section, Seismological Society of America.
R. R. Bodle, Editor. Address: U.S. Coast and Geodetic Survey.
Washington, D.C.
Vol. 8
March, 1937
No. 4
TWELFTH ANNUAL MEETING, JUNE 11, 12, 1937
The Twelfth Annual Meeting of the Eastern Section of the Seismologioal Society of America will be held at Saint Louis University, Saint Louis, Missouri,
on June 11, 12, 1937. The success and benefits of the meeting depend on YOUR
cooperation!
Offers to present papers should be sent to the Secretary Pro Tem (Anthony
J. Westland, S.J., Saint Louis University, 15 North Graxid Boulevard, Saint Louis,
Missouri). Please have in the hands of the Secretary Pro Tem before May 15 the
title of your paper, the time required, and whether or not slides will be used.
SECRETARYSHIP
It is with regret that we have to announce that F. W. Sohon has found it
necessary on account of ili health to relinquish his duties as Secretary of the
Eastern Section. He was elected to the post at the Ottawa meeting in 1935 and
continued in the office at the 1936 meeting in Washington. Anthony J. Westland,
Saint Louis University, has been appointed Secretary Pro Tem.
EARTEQUAKE OBSERVATIONS AND EARLY USE OF THE PENDULUM
In "The New Madrid Earthquake" by Fuller (U. S. Geological Survey) referenoe is made to the "History of Louisville from its earliest settlement till the
year 1852" by Jared Brooks. Fuller states that the reference gives a complete
list of observed shocks, pendulum observations, weather, etc., at Louisville
Erom December 16, 1811 to May 1812. It seems likely this may have been the first
time that the pendulum was used in this country for earthquake observation purposes.
AMATEUR SEISMOLOGY
Owing to the interest which has been developing in amateur seismology during recent years, the Chairman has found it desirable to appoint a committee to
promote this field of activity. The committee appointed in February is as follows: Dr. J. B. Macelwane, Chairman; Dr. L. Don Leet, Dr. Ernest L. Hodgson,'
Dr. H. M. Rutherford, Mr. H. E. McComb, and Mr. Albert G. Ingalls.
AN INTRODUCTION TO THE SEISMOGRAPH FOR THE AMATEUR
Earthquakes have been a source of destruction encountered by man since the
earliest historicsl times. The causes are not yet fully understood even though
-2modern instruments have furnished valuable data from which many scientific facta
have been deduced. The question hes never ceased to be en intriguing one. Possibly the earliest known attempt to record the motion of en earthquake may be attributed to the Chinese (136 B.C.), who observed the direction from which en
earthquake appeared to come. This was done by placing balls in niches facing in
various directions. They were arranged so that only a comparatively small movement was necessary to dislodge them. Should the balt facing in any given direction fall from its niche,, it was concluded that the ground had moved in that
direction.
Later the simple pendulum came into use (see Figures 1 and 2). It was
found that the pendulum support would move with the earthquake motions while the
heavy pendulum bob responded slowly, especially if it were a long pendulum with
a heavy weight. Advantage was taken of this fact to get a crude record of the
actual movements of the ground beneath the pendulum. This was accomplished by
placing a rather stiff whisker on the pendulum and allowing it to touch a smooth
plate covered with soot. The plate of course moved with the ground and thus
wrote a record of the ground mvvements.
It was found, however, that these records were not satisfactory for several
reasons. They gave no information on time and also the recording pendulum itself would soon begin to swing in its own natural period. This letter effect
meent that the real earth movements were recorded at the same time the natural
pendulum movements were recorded, with no way of distinguishing between them.
The most that could be learned from such records was the approximate amount of
the Earth's displaoement at the instrument site. There was no magnification of
the recorded movements.
In order to reduce the fictitious effect of the naturel period of the pendulum, it was found necessary to make the pendulums very long and heavy. To
overcome this situation the "horizontal" pendulum was developed. The "horizontal" pendulum is the principle on which most of the present-day seismographs
are constructed. There are many exceptions, but they probably should not be
considered here.
With the "horizontal" pendulum, one is able to obtain a naturel vibration
period of the pendulum bob that is the equivalent of a very long simple pendulum.
The result is accomplished in comparatively small space, while the simple pendulum would have to be about 80 feet long to obtain a period of 10 seconde. The
"horizontal" pendulum een be made to give equivalent periode in lees than a cubie
Poot of space.
There is another very important difference between the two pendulums. While
the simple pendulum records horizontal motion in any direction, the "horizontal"
pendulum can only record motion which is perpendicular to the direction in which
it extends. This is a very desirable characteristic einee two suoh pendulums
may be set to record motions which are at right angles to each other.
Now, if the two components were to record the ground movements, the actual
direction and extent of a movement could be determined for any instant during the
disturbance provided the effect of the natural vibration period of the pendulum
can be eliminated from the record. This een be accomplished by applying a damping effect to the pendulum.
If a 10-second pen.dulum is allowed to swing free, it will continue to oscillate with slightly diminishing amplitude for several minutes. Now, if a
"braking" or "damping" effect is applied so that each successive departure from
-3the point of rest is 1/10 that of the preceding departure, we will have succeeded to a large extent in preventing oscillation of the pendulum in its natural
period while at the same time allowing it to respond to the effect of passing
seismic waves on its support.
There are several ways of producing the damping effect. Probably the most
appropriate for consideration here is the magnetic method. This has been accomplished in at least one instante in a manner indicated in Figures 5 and 6.
If the differential motion between the seismograph pendulum and the ground
were not magnified, there would be no legible record except in the case where the
instrument was located in or very near the strongly shaken area.
There are two methods of magnification which may be appropriately discussed
here, namely, (a) mechanical and (b) optical.
(a) The mechanical magnification method employs the use of smoked paper on
a recording drum. Usually the recording drum is made to rotate once an hour
either by a driving clock or an electric motor. The axle of the drum extends a
little more than the normal width of the drum on one side of the drum and is
threaded like a screw. The threaded axle rests on n shaped rollers, thus pulling.the drum sideways as it rotates. The magni£ying lever is attaahed to the
pendulum as shown in Figure 8, and the point of a recording stylus rests very
lightly in the Boot on the drum surface as indicated in the Figure.
In the optical method, photographic paper is used on the drum instead of
smoked paper (see Figure 7). Though a number of schemes are employed, one of
the more simple calls for a plane mirror which may be placed on the pendulum
near the pivot "A" indicated in Figure b. When the pendulum moves from its rest
position, the mirror will then turn through the same angle. It must be placed
near the pivot "A" to avoid any appreciable change in focal distance when the
penaulum is moved. Now, if a light from a narrow slit were to fall on this mirror, the reflection could be recorded. The angular motion of the reflected
light beam in this case is double that of the pendulum. In practice, multiplying levers are frequently used to increase the angular motions of mirrors (in
photographic recording) and recording pens (in the case of mechanical recording).
Summary--The foregoing has covered the more important principles of the
seismograph. An attempt has been made to give a general idea of some of the
methods employed without going into details and specifications. A detailed consideration would have involved, among other things, the formule for the time or
period of oscillation of a simple pendulum where T (time of one oscillation) is
equal to 21r times the square root of L over g, L is the length of the pendulum,
and g is the force of gravity (T = 2w
). It would have involved the explanation of the application of this formula to the horizontal pendulum because of
the reduction in the effective force of gravity on the pendulum. The portion of
gravity force which can act to make the horizontal pendulum oscillate is directly proportional to the sine of the angle of inclination "i" of the plane of oscillation as shown in Figure 5. (This assumes that the pendulum makes a right
angle with the supporting column as indicated in the previous Figures.)
Explanation of Figures
Fig. 1--Represents a plane surface set in a vertical position. A simple pendulum, consisting of a bob on a rigid rod, swings in front of the plane
by means of an axle rotating in a bearing contained in the plane.
Fig. 2--This shows a side view of Figure 1.
-4Fig. 3--Now, if the plane surface (1) is tilted back until it slopes at a 45 0
angle, the sample pendulum will have been changed to one whioh will
swing through a plans making a 45 angle with the horizontal. It has
thus been partly converted to a horizontal pendulum. Now, from the
parallelogram of forces and the inclined plane demonstration which is
explained in most elementary text-books on physics, we know that the
full force of gravity is no longer acting to restore the pendulum to
its normal position. Only that portion is acting whioh is directed
down the plane parallel to the normal position of the pendulum, and only that portion of the force of gravity acting along the direction of
the plane affeots the motion of the pendulum when it is out of its
normal position. SINCE IN THIS POSITION THE FORCE WHICH CAN ACT ON THE
PENDULUM RAS BEEN REDUCED, THE TIME OF OSCILLATION OF THE PENDULUM RAS
BEEN INCREASED.
°
Fig. 4--This is a side view of the plane from which the pendulum is supported at
an angle of 45 from the horizontal.
°
Fig. 5--For the same reason given in explaining Figure 3, the force of gravity
which could act on the pendulum to restore it to a normal position would
be reduced to a very small amount if the supporting plane were to be inclined so that it made only en angle of 10 or 2 with the horizontal.
In order to allow this very wenk force to act on the pendulum without
hindrance from friction, the seismologist has constructed a "horizontal"
pendulum such as the one in this Figure. (A) is a thrust bearing in
the foren of a pivot which supports the end of the boom connecting with
the maas (C), and (B) is a tension bearing usually in the form of a
pivot to which the supporting wires from the maas are fastened. NOW
WITH A SLOW-MOTION ADJUSTMENT AT EITHER (A) OR (B) WE CAN RAISE AND
LOWER THE MASS AND THUS CHANGE THE INCLINATION OF ITS PLANE OF OSCILLATION OR THE ANGLE (i) IN THE FIGURE. IF THE ANGLE BETWEEN THE PLANE OF
OSCILLATION AND THE HORIZONTAL IS VERY SMALL (AS EXPLAINED FOR FIGURE
3) THE EFFECTIVE RESTORING FORCE WILL BE VERY SMALL AND THE PENDULUM
WILL MOVE VERY SLOWLY. IF THERE IS NO FRICTION AT POINTS (A) AND (B),
THE PENDULUM WILL OSCILLATE FREELY FOR A LONG PERIOD. AN OSCILLATION
TEST TO SEE HOW LONG THE PENDULUM WILL SWING FREELY AND TO SEE IF IT
WILL RETURN TO ITS NORMAL POSITION AFTER BEING DISTURBED IS ONE OF THE
CHIEF WAYS TO LEARN IF A SEISMOGRAPH PENDULUM IS IN CORRECT ADJUSTMENT.
(These tests are made without damping, which is described under Figure 6.)
°
Fig. 6--This shows the method of applying magnetic damping to a seismograph
pendulum. The damping vane (V) is passed between the poles of horseshoe magnets which are rigidly fixed in the positions shown. The vane
is made of copper so that when it is moved through the magnetic fields
of the magnets a resistance is set up tending to retard the motion.
This resistance increases and decreases with the velocity of the vane.
Now, if the magnetic field acting on the vane is adjusted so that in en
oscillation test of the pendulum each succeeding departure from the
normal position is 1/10 the previous departure, the damping influence
is ordinarily considered satisfactory. In this way the pendulum is
free to respond to the effects of any passing earthquake waves, but at
the same time it is prevented from swinging in its own period and complicating the record.
Figs. 7 and 8--The description of these Figures is contained in the text.
-5-
31^
PIVOTED MIRROR
BOOM
MASS
/
^
7
W
IGHT '^
OR DING DRUM
-6-
PIVOTED AXLE
MASS
MAGNIFYING LEVER
0
ING DRUM
ê.
8
HH
[j
REFERENCES FOR AMATEURS
(a) "How to build a simple seismograph" by Baldridge in Popular Science for November 1935.
(b) "How to make a simple seismograph" in the Volcano Letter for March 1936 (a
monthly publication of the National Park Service, U. S. Department of the
Interior).
(c) "Amateur seismology" by Albert G. Ingalls in the Scientific American for
April 1936.
(d) "Seeburger seismograph" described in the Volcano Letter for July 1936.
(e) "Friction of the writing stylus" by T. Hagiwara in the Bulletin of the
Earthquake Research Institute, Tokyo, Vol. XI, Part 1, March 1933.
MEETING OF THE GEOLOGICAL SOCIETY OF AMERICA
The mid-winter meeting of the Geological Society of America in Cincinnati
touched on seismology in a number of cases. Professor A. J. Miller (University
of California at Los Angeles) discussed "The oondition of the earth's crust in
Southern California." N. H. Heek talked on "Seismological investigations in the
Western Mountain region." H. M. Rutherford discussed the statistical method of
arriving at velocities in refleotion work. L. B. Slichter demonstrated his instrument which has a wide range of application. Professors Perry of Williams
College, Conant of Cornell University, and Stechschulte of Xavier University,
Cincinnati, were present.
ere
OHIO EARTHQUAKES, MARCH 1937
Dy V. C. Stechschulte, S.J.
On March 2, 1937, about 9:48 a.m., E.S.T., most of Ohio and Indiana feit
with varying degrees of intensity en earthquake which had its center in Shelby
County, Ohio, with notable damage at the village of Anna. Here the school was
injured to such an extent that it was deolared unsafe. Many chimneys were
thrown down and other minor damage done. At 12:45 a.m., E.S.T., on March 9,
another shock of much greater intensity occurred, centering apparently in the
same place as the previous quake. Further damage was done to the school. Two
small brick churches were seriously injured, while many dwellings were damaged
to a greater or lesser extent. However, there were no injuries, while the
school authorities were glad to have taken out $30,000 worth of earthquake insurance after the shock which occurred in this same region on September 20,
1931. Chimneys were thrown down in Sidney, Wapakoneta, and other towns and
villages. The shock was feit as far away as St. Louis, so that the total area
over which it was observed was probably about 150,000 square miles. A more
exact determination of the extent awaits the study of replies to questionnaires
circulated by St. Louis University and by Xavier University.
Many interesting phenomena in regard to sound heard and sky illumination
seen have been reported. The character of the rotation of tombstones in a number of cemeteries near Anna has raised some interesting questions.
A study of the instrumental data is being made by Dr. V. C. Stechschulte of
Xavier University, Cincinnati. It is of interest to note that the earthquakes
veere recorded at an amateur seismograph station about ten miles from the epicenter.
RECEIVERS FOR RADIO TIME-SIGNALS
By B. C. McGee
The short-wave time-signals transmitted by the United States Naval Observatory would probably be the most easily received by an amateur seismologist. The
signals transmitted are not modulated and cannot be received by a broadcast-type
short-wave receiver unless it is equipped with a beat oscillator. This is a
small oscillating circuit, like a miniature transmitter, which introduces into
the receiver circuits a continuous train of waves differing slightly in frequency from the waves being received. The heterodyning or beating between the two
sets of waves makes the unmodulated signal audible. Such beat oscillators are
made by RCA Manufacturing Company and possibly by other manufacturers. They are
not expensive, and could easily be attached by a service man. They are usually
intended to be used in conjunction with AC-operated sets only.
If a special receiver for time signals is desired, one of the "communications" type is suggested. Such a receiver would have a beat oscillator built
into it, and provision for listening either by loud speaker or head phones.
These sets are made by RCA, National Company, Hammarlund, Hallicrafters, and
others, at prices ranging from about $30 to $250, and are advertised in "Radio
News" and "Q5•" Some of the more expensive are equipped to receive the longwave transmissions of the Naval stations.
Care should be taken to ascertain that a proposed set will receive the required frequenties. A few of the "communications" receivers are built for
-8operation on the amateur frequencies only, and could not be used for receiving
time signals.
If the family receiver, equipped with a beat oscillator, is to be used for
time-signal reception, a permanent-magnet type of loud speaker may be placed
near the marking clock and connected to the receiver by a pair of wires, with a
switch to disconnect it when not needed. Such an extension speaker could be installed by eny service man.
NEW EQUIPMENT
Benioff seismographe have been installed at a number of stations in recent
months and others are projected or about to be installed. Information reaching
the Editor indicates that the following stations are included in the groups just
mentioned: Burlington, Vermont (University of Vermont); Williamstown, Massachusetts (Williams College); Pittsburgh, Pennsylvania (University of Pittsburgh);
Fordham, New York (Fordham University); and Ottawa, Canada (Dominion Observatory).
STRONG-MOTION RECORDS
During the shock of March 8, 1937, seven strong-motion records were obtained in the Los Angeles area. The shock centered on the Hayward fault a few
miles north of the University of California campus.
The Southern California shock of March 25 produced fifteen strong-motion
records. It is interesting to note that some of the instruments failed to
operate in the same area where others did. This was probably due to the fact
that the intensity was just about the magnitude at which the starters were set
to function. A slightly greater intensity would probably have started all the
instruments. This shock centered on the San Jacinto fault in a sparsely settled
region in Southern California (33?4 north latitude, 116:7 west longitude).
CALIFORNIA GROUND VIBRATIONS
A Coast and Geodetic Survey party under Lieut. W. D. Patterson has been
operating in Southern California for several months making ground vibration
tests and testing equipment. Results of this work have proved beyond doubt that
similar ground periods exist in the Los Angeles plain at points about 18 miles
apart. Many of the periods induced were the same as those recorded at the time
of the Long Beach earthquake.
CANADIAN STATIONS CONSOLIDATED
A notice with the December 1936 issue of the Ottawa instrumental reports
indicates the consolidation of all Canadian seismograph stations. The work is
now organized under the Dominion Observatory, with the central station at Ottawa, and auxiliary stations at Halifax, Nova Scotia; Seven Falls and Shawinigan
Falls, Quebec; Toronto, Ontario; Saskatoon, Saskatchewan; and Victoria, British
Columbia. The consolidation took effect on December 1, 1936.
-9WILLIA"IS COLLEGE STATION
February 22, 1937, marked the date of the official opening of the seismograph station at Williams College, Williamstown, Massachusetts (42 ° 42' 51"
north latitude, 73" 12' 40" west longitude). The event was marked with ceremonies which were attended by alumni of the College and a number of invited
guests. Daniel Linehan of Weston College and N. H. Heck of the Coast and Geodetie Survey were in attendance. The latter talked on the contribution of Williams
College to seismology of New England, of the United States, and of the earth.
An instrumental report on recorded earthquakes was recently received at the
Coast and Geodetic Survey. This report indicates that the Station has gotten
off to a good start.
A. MOHOROVICIC
Word has been received of the death of A. Mohoroviéi6 on December 8, 1936,
at the age of 80 years. He was widely known for his seismological investigations and espeeially for his work on sei'smological tables for nearby earthquakes and for his studies on the depth and character of the surface layers. He
was formerly director of the Geophysical Institute of Zagreb, which he founded,
and professor at the University of Zagreb.
BUILDING DESIGN
The Engineering News-Record for March 18, 1937, has an article by Harry W.
Bolin on "Earthquake-resistant design for new school buildings." He describes
the results of experience in applying California's structural law of 1933 and
explains the methods and details used in buildings of wood, steel, concrete, and
brick in the Los Angeles area.
REPAIRING EARTHQUAKE DAMAGE
The above is the title of an article appearing in the Engineering NewsRecord for March 11, 1937. J. E. Byers, the author, states that the rehabilitation problems after the 1933 earthquakes in California demanded analytical
methode without precedent and resulted in a classification of buildings according to seismic resistance. Five schemes were adopted for repairing the earthquake damage in Los Angeles.
DYNAMIC METHODS OF DESIGN
At a recent meeting of the American Concrete Institute in New York, J. J.
Creskoff gave a paper on dynamic methods of building design and stressed the
importante of reinforced concrete in earthquake-resistant design.
LIST OF HIGH DAMS
Seismologists and engineers who are interested in the effects of earthquakes on such structures will find the "List of all dame in the world 100 feet
high and over" a valuable referonce. It appears in the Engineering News-Record
for December 10, 1936.
-10THE EARTH'S INTERIOR
The Scientific Monthly for March 1937 contains an article by L.
L. H. Adams on
its nature
composition." This
This article
article very
very effeceffec"The
"The earth's
earth's interior,
interior, its
nature and
and composition."
tively summarizes the present-day
present-day knowledge
knowledge on
on this
this subject.
subject.
ARTICLES IN
IN THE SKY
SKY
"Eight thousand earthquakes per year,
year, roughly
roughly speaking"
speaking" is
is the
the title
title of
of en
an
article by Dr.
Dr. Chester A. Reeds
Reeds which
which appeared
appeared in
in The
The Sky
Sky (Vol.
(Vol. 1,
1, No.
No.5)
for
5) for
March 1937,
1937, a publication of the
An article
article
the American
American Museum
Museum of
of Natural
Natural History.
History. An
on "Earthquakes and astronomy"
astronomy" by
by N.
N. H.
H. Heck
Heck also
also appeared
appeared in
in the
the same
same number.
number.
PERSONALIA
Announcement has recently been made of the appointment of Professor William
T. Thom, Jr.
Jr. to
to the
the Blair
Blair Chair
Chair of
of Geology
Geology at
at Princeton.
Princeton. Professor
T.
Professor Thom
Thom sucsucceeds
Fromthe
the list
list of
of changes
changes in
in the
the
ceeds the
the late
late Professor
Professor Alexander
Alexander H.
H. Phillips.
Phillips. From
faculty at the Massachusetts
Massachusetts Institute
Institute of
of Technology,
Technology, we
we learn
learn that
that Mr.
Mr. Arthur
Arthur C.
C.
promoted to
to the
the rank
rank of
of Assistent
Assistant Professor.
Professor.
Ruge has been promoted
GOLD MEDAL
"Nature"for
"The
"Nature"for January
January 16,
16, 1937,
1937, carries
carries the
the following
following announcement:
announcement: "The
Medal of the Royal Astronomical Society
Gold Medal
Society has
has been
been awarded
awarded to
to Dr.
Dr. Harold
Harold
Jeffreys for his researches into
into the
the physics
physics of
of the
the Barth
earth and
and other
other planets
planets and
and
for his contributions to
to the
the study
study of
of the
the origin
origin and
and age
age of
of the
the solar
solar system."
system."
EPICENTERS
Since
Since the
the last
last issue
issue the
the following
following epicenters
epicenters have
have been
been located.
located. Through
cooperation of Science Service
Service data
data are
are exchanged
exchanged between
between the
the Coast
Coast and
and Geodetic
Geodetic
Survey and
The folfoland the
the Central
Central Office
Office of the
the Jesuit Seismological
Seismological Association.
Association. The
lowing
The organiorganilowing are
are means
means of the two determinations
determinations when
when both are available.
available. The
zations making the determinations are
are indicated
indicated by
by STL
STL for
for St.
St. Louis
Louis and
and CS
CS for
for
Coast and Geodetic
Geodetic Survey.
Survey.
Date
1936
Oct. 23
Nov. 2
Nov.
Nov.
Nov. 2
Nov. 13
Nov. 19
Nov. 22
Dec. 20
Dec. 21
1937
Jan. 7
Jan. 25
Feb. 7
Feb. 21
Organizations
and remarks
Time
G.C.T.
h m
m
6 24.4
14 58.2
20 45.9
12 31.6
21 10.4
21
18 19.4
2 43.5
19 03.1
61.0
47
37.6
56.8
14.2
14.1
13.8
53.1
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
149.3
157
142.0
162.6
90.8
90.6
88.7
131.8
W
W
E
E
E
E
E
l:i:
W
W
W
W
W
W
W
W
STL,
STL, CS
CS, provisional
STL, CS
STL,
STL, CS
STL,
STL, CS
STL,
STL, CS
STL,
STL, CS
STL,
STL, CS
STL,
20.6
34.0
41.6
02.7
35.8
11.3
41
45.1
N
N
S
S
N
N
N
N
98.1
163.6
124
148.3
118.3
E
E
E
E
W
W
E
E
STL, CS
S'1;L,
STL,
STL, CS
CS
STL, CS
STL,
13
6
4
7
Lat.
g.
Long.
.
00
00