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 Effects (source http://earthquakescanada.nrcan.gc.ca) # per year (worldwide) Source: USGS 1 Not perceptible to people? -100 2 1,300,000-10 3 Often felt, but rarely cause damage. 130,000 -- 4 13,000 10 5 At most slight damage to well-designed buildings. Can cause major damage to poorly constructed buildings over small regions. 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 7 "Major" earthquake. Can cause serious damage over larger areas. 8 "Great" earthquake. Can cause serious damage and loss of life in areas several hundred kilometers across. 9 Rare great earthquake. Can cause major damage over a large region over 1000 km across. 1300 100 150 1000 20 10,000 1 100,000 Strength compared to a Magnitude 3 quake <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 255,000 1 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, 856 2 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, 893 2 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 70,000 100,000 3 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 7.2 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?
The depression of the asthenosphere beneath mountain belts due to loading followed by rebounding as erosion occurs. Isostasy (Isostacy)
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 dhaywick@southalabama.edu This is a free open access lecture, but not for commercial purposes. For personal use only.