Earthquakes

What are What are Earthquakes?Earthquakes?

The shaking or trembling caused by The shaking or trembling caused by the sudden release of energythe sudden release of energy

Usually associated with faulting or Usually associated with faulting or breaking of rocksbreaking of rocks

Described by the Elastic Rebound Described by the Elastic Rebound TheoryTheory

What is the What is the Elastic Rebound TheoryElastic Rebound Theory??Explains how energy is stored Explains how energy is stored

in rocksin rocks

– Rocks bend until the Rocks bend until the strength of the rock is strength of the rock is exceededexceeded

– Rupture occurs and the Rupture occurs and the rocks quickly rebound to rocks quickly rebound to an undeformed shapean undeformed shape

– Energy is released in Energy is released in waves that radiate outward waves that radiate outward from the faultfrom the fault

What is the What is the Elastic Rebound TheoryElastic Rebound Theory??

Elastic Rebound

Type of Faults (A Review)Type of Faults (A Review)

Normal

Reverse

Strike-Slip

Seismic WavesSeismic Waves

Through no fault of our own, seismic Through no fault of our own, seismic waves are generated from the breaking of waves are generated from the breaking of the rockthe rock

These waves of energy that travel through These waves of energy that travel through the Earth after an earthquakethe Earth after an earthquake

• Some of these waves are what you feel Some of these waves are what you feel during an earthquakeduring an earthquake

Types of WavesTypes of WavesSurface – travel along the surface, cause the most Surface – travel along the surface, cause the most damage (Your teacher may divide these further into damage (Your teacher may divide these further into Love and Raleigh Waves) (Slower than Body)Love and Raleigh Waves) (Slower than Body)Body – travel through the EarthBody – travel through the Earth

• P waves- pushes and pulls the rock (twice as fast as P waves- pushes and pulls the rock (twice as fast as S wave)S wave)

• S wave – slower, displaces rock at right angles, S wave – slower, displaces rock at right angles, don’t travel through liquidsdon’t travel through liquids

P & S AnimationP & S AnimationP,S & Surface AnimationAnother P,S & Surface Animation

Seismic Wave Motion

S S Waves Waves Prove Prove Liquid Liquid Outer Outer CoreCore

Proof of Moho Proof of Moho ((Mohorovičić discontinuity)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 Proof of Moho Moho

Notice the increase in velocity around 80 meters, just before the transition to the mantle!

Focus and EpicenterFocus and Epicenter

Focus:Focus: the point at which energy is the point at which energy is released, causing the earthquakereleased, causing the earthquake

Epicenter:Epicenter: the point on the surface of the the point on the surface of the Earth that is directly above the earthquake Earth that is directly above the earthquake focus.focus.

Earthquakes generate seismic Earthquakes generate seismic waves which can be detected waves which can be detected

with a sensitive instrument with a sensitive instrument called a called a seismographseismograph..

Seismographs

Perhaps the earliest Perhaps the earliest seismograph was invented in seismograph was invented in

China A.D. 136 by a m an China A.D. 136 by a m an named Choko. named Choko.

Richter Scale Richter Scale Measures magnitude of an earthquakeMeasures magnitude of an earthquake

1-101-10

2 is the smallest able to be felt by humans2 is the smallest able to be felt by humans

Mercalli ScaleMercalli Scale

Measures intensityMeasures intensity

Uses Roman Uses Roman numeralsnumerals

I – XIII – XII

I – no damageI – no damage

XII – total damageXII – total damage

Associated HazardsAssociated Hazards

Landslides

Volcanic eruptions

Tsunamis

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

Banda Aceh, Sumatra, before tsunamihttp://geo-world.org/tsunami/

Banda Aceh, Sumatra, after tsunamiAlso: http://www.digitalglobe.com/

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

Latest Earthquakes in the World Past 7 days

Film ClipsFilm Clips

Destruction

Earthquake Swallows Car

Seismic Wave Demonstrator

The EndThe End