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Earthquakes
What are Earthquakes?
The shaking or trembling caused by the sudden release of energyUsually associated with faulting or breaking of rocksDescribed by the Elastic Rebound Theory
What is the Elastic Rebound Theory?Explains how energy is stored
in rocks–Rocks bend until the
strength of the rock is exceeded
–Rupture occurs and the rocks quickly rebound to an undeformed shape
–Energy is released in waves that radiate outward from the fault
What is the Elastic Rebound Theory?
Elastic Rebound
Type of Faults (A Review)
Normal
Reverse
Strike-Slip
Seismic Waves
Through no fault of our own, seismic waves are generated from the breaking of the rock
These waves of energy that travel through the Earth after an earthquake
• Some of these waves are what you feel during an earthquake
Types of WavesSurface – travel along the surface, cause the most damage (Your teacher may divide these further into Love and Raleigh Waves) (Slower than Body)Body – travel through the Earth• P waves- pushes and pulls the rock
(twice as fast as S wave)• S wave – slower, displaces rock at
right angles, don’t travel through liquidsP & S AnimationP,S & Surface AnimationAnother P,S & Surface Animation
Seismic Wave Motion
Proof of Moho (Mohorovičić discontinuity)
• Moho: The dept at which the P-wave velocity exceeds 8.1 Km/S is referred to as the moho (after the seismologist Mohorovicic). The moho is both a seismic and a compositional boundary, marking the transition between crust and mantle materials.
Proof of Moho
Notice the increase in velocity around 80 meters, just before the transition to the mantle!
Focus and EpicenterFocus: the point at which energy is released, causing the earthquake
Epicenter: the point on the surface of the Earth that is directly above the earthquake focus.
Earthquakes generate seismic waves which can be detected
with a sensitive instrument called a seismograph.
Seismographs
Perhaps the earliest seismograph was invented in
China A.D. 136 by a m an named Choko.
Richter Scale Measures magnitude of an earthquake1-102 is the smallest able to be felt by humans
Mercalli Scale
Measures intensityUses Roman numeralsI – XIII – no damageXII – total damage
Associated Hazards
Landslides
Volcanic eruptions
Tsunamis
Tsunami
Fault Generating Tsunami Fault Generating Tsunami
Tsunami Damage, Gleebruk, Indonesia
Chedi Resort, Phuket, Thailand, wave height ~4+ m (?, from estimates of water level from beach umbrellas on grassy area above the beach)
Damage in Banda Aceh
Earthquake and Tsunami Damage, Banda Aceh, Sumatra
Earthquake and Tsunami Damage,
Sri Lanka
Geist, Titov and Synolakis, Tsunami: Wave of Change, Scientific American, January, 2006.
Train and tracks destroyed, SW coast of Sri Lanka
Tsunami wave trough, Sri Lanka coast
Commonly, the water recedes (a wave trough) significantly for a few minutes before the first wave crest arrives. People often go out to explore the beach or gather fish or shells at that time.
Tsunami wave, Sri Lanka; note strong current
Another Hazard Associated with Earthquakes
Liquefaction
San Francisco are built on sandy soil or fill. Many homes built on this type of soil were badly damaged during the 1989 Loma Prieta earthquake by liquefaction.
Liquefaction occurs in saturated soils, that is, soils in which the space between individual particles is completely filled with water. This water exerts a pressure on the soil particles that influences how tightly the particles themselves are pressed together.
Model of liquefaction
Example of liquefaction
Film Clips
Destruction
Earthquake Swallows Car
Seismic Wave Demonstrator
The End
