UNIVERSITY OF SOUTH ALABAMA
GY 111: Physical Geology
Lecture 31: Mountain Building 1:
Isostasy and Thrusting
Last Time
Earthquakes
A) Earthquake intensity and magnitude
B) Seismographs
C) Case Studies
Web notes 29:
GY 111 Lab Manual Chapter 7
Seismic Waves
P and S-waves are called body waves because they travel through
the Earth.
P-waves travel through all media and are the fastest (4+ km/s)
S-waves cannot pass through liquids and are slower (3+ km/s)
Seismographs
Seismic waves are recorded
using seismographs.
The traces are called
seismograms.
More about seismograms shortly, but
first… Earthquake magnitude.
Earthquake Magnitude
The “intensity” of an earthquake can be measure through one of
two ways.
1) A “people” method: Modified Mercalli Intensity Scale (I to XII)
2) A geophysical method: Modified Richter Scale (1 to 10)
Earthquake Magnitude
Earthquake Magnitude
Magnitude
1
Effects
(source http://earthquakescanada.nrcan.gc.ca)
Not perceptible to people
2
3
Often felt, but rarely cause damage.
4
# per year
(worldwide)
Source:
USGS
Strength
compared to a
Magnitude 3
quake
?
-100
1,300,000
-10
130,000
--
13,000
10
5
At most slight damage to well-designed buildings. Can
cause major damage to poorly constructed buildings
over small regions.
1300
100
6
Can cause damage to poorly constructed buildings and
other structures in areas up to about 100 kilometers
across where people live. Substantial deaths, especially
if epicenter is in a major city
150
1000
7
"Major" earthquake. Can cause serious damage over
larger areas.
20
10,000
8
"Great" earthquake. Can cause serious damage and
loss of life in areas several hundred kilometers across.
1
100,000
9
Rare great earthquake. Can cause major damage over a
large region over 1000 km across.
<1
1,000,000
10
Impossible unless you make bad movies
10,000,000
Death 101
The worst earthquakes
(as far as death is
concerned)
Date
Location
Deaths
Magnitude
Jan. 23, 1556
Shansi, China
830,000
~8
July 27, 1976
Tangshan, China
255,0001
7.5
Aug. 9, 1138
Aleppo, Syria
230,000
n.a.
Dec. 26, 2004
off west coast of northern Sumatra
225,000+
9.0
Dec. 22, 8562
Damghan, Iran
200,000
n.a.
May 22, 1927
near Xining, Tsinghai, China
200,000
7.9
Dec. 16, 1920
Gansu, China
200,000
7.8
March 23, 8932
Ardabil, Iran
150,000
n.a.
Sept. 1, 1923
Kwanto, Japan
143,000
7.9
Oct. 5, 1948
Ashgabat, Turkmenistan, USSR
110,000
7.3
Dec. 28, 1908
Messina, Italy
70,000–
100,0003
7.2
Sept. 1290
Chihli, China
100,000
n.a.
Oct. 8, 2005
Pakistan
80,361
7.6
Nov. 1667
Shemakha, Caucasia
80,000
n.a.
Nov. 18, 1727
Tabriz, Iran
77,000
n.a.
Dec. 25, 1932
Gansu, China
70,000
7.6
Nov. 1, 1755
Lisbon, Portugal
70,000
8.7
May 31, 1970
Peru
66,000
7.9
May 30, 1935
Quetta, Pakistan
30,000–
60,000
7.5
Weird Earthquake Stuff
1) Japanese video coverage of the Kobe 1993 earthquake
2) Japanese Tsunami 2011
3) New Zealand 2016 observations
4) Other near death experiences in New Zealand earthquakes
5) Liquefaction and building failures (Japan, 1960)
6) California bridge collapses (1974, 1994)
Indonesia, December 26, 2004
Seismicity of Australia, Indonesia and New Zealand: 1990-2000
Source: http://earthquake.usgs.gov/
Indonesia Geopolitical Map
Source: http://earthquake.usgs.gov/
Indonesia Tectonic Map
Source: http://earthquake.usgs.gov/
Indonesia Seismicity Map
Source: http://earthquake.usgs.gov/
Seismograms
December 26, 2004
Tsunami
Source: IOC
Tsunami Arrival Times (hours:minutes)
The Aftermath
230,000? dead
Whole villages
washed away
Coastlines
permanently
changed
Source: http://wcatwc.arh.noaa.gov
IOC ICG/ITSU
“Early” Warning
System
SEISMOGRAPHIC NETWORK
Today’s Agenda
Mountain Building 1
A) Distribution of mountain belts (the return of plate tectonics)
B) Isostasy and the Rock Cycle (again)
C) Thrust Faults in the Rockies
Web notes: 31
Mountain Belts
Mountain Belts
Mountain Belts
Mountain Belts
New Mountains
Old Mountains
Mountain Belts
Northern
Transect
Southern Transect
Mountain Belts
The older the mountain range, the more time erosion and
weathering has had to destroy the mountains.
Mountain Belts
The older the mountain range, the more time erosion and
weathering has had to destroy the mountains.
The northern Appalachian Mountains are older than the
southern Appalachian Mountains (500 MA versus 300 MA), so
it stands to reason that they would be more eroded.
Mountain Belts
The older the mountain range, the more time erosion and
weathering has had to destroy the mountains.
The northern Appalachian Mountains are older than the
southern Appalachian Mountains (500 MA versus 300 MA), so
it stands to reason that they would be more eroded.
The surprising thing is that the southern Appalachians are still
mountains after 300 Million Years of erosion….
Why are the mountains still there?
Isostasy (Isostacy)
The depression of the
asthenosphere beneath
mountain belts due to loading
followed by rebounding as
erosion occurs.
Isostasy (Isostacy)
The depression of the
asthenosphere beneath
mountain belts due to loading
followed by rebounding as
erosion occurs.
Styrofoam sheets on water
Isostasy (Isostacy)
The depression of the
asthenosphere beneath
mountain belts due to loading
followed by rebounding as
erosion occurs.
erosion
Isostasy (Isostacy)
The depression of the
asthenosphere beneath
mountain belts due to loading
followed by rebounding as
erosion occurs.
isostasy
Isostasy (Isostacy)
The depression of the
asthenosphere beneath
mountain belts due to loading
followed by rebounding as
erosion occurs.
erosion
Isostasy (Isostacy)
The depression of the
asthenosphere beneath
mountain belts due to loading
followed by rebounding as
erosion occurs.
isostasy
Isostasy (Isostacy)
The depression of the
asthenosphere beneath
mountain belts due to loading
followed by rebounding as
erosion occurs.
erosion
Isostasy (Isostacy)
The depression of the
asthenosphere beneath
mountain belts due to loading
followed by rebounding as
erosion occurs.
isostasy
Isostasy (Isostacy)
The depression of the
asthenosphere beneath
mountain belts due to loading
followed by rebounding as
erosion occurs.
Erosion
Isostasy (Isostacy)
When you build up mountains, depression of the asthenosphere
produces “continental roots” below the continental crust
Isostasy (Isostacy)
Isostasy will continue as long as continental roots still exist.
Once isostasy stops, the mountains will get completely eroded
away (it takes about 500 MA for this to occur).
The Rock Cycle
Mountain belts involve all types of rocks and minerals and all
types of geological processes.
For example, consider the Himalayan Mountains
The Rock Cycle
The Rock Cycle
The Rock Cycle
So in conclusion, mountain
building (and mountain erosion)
are excellent examples of the rock
cycle in action.
Incidentally, mountain building is
itself, cyclic (see you in GY 112!)
Thrust Faulting in the Rockies
Today’s Homework
1. Start Prepping for the Final Exam
2. Assignment 4 due
3. Mobile Rock and Gem Society Show
Next Time
1.
Appalachian Mountains, final prep
GY 111: Physical Geology
Lecture 31: Mountain Building 1
Instructor: Dr. Doug Haywick
[email protected]
This is a free open access lecture, but not for commercial purposes.
For personal use only.