Magnitude 7.6, Sumatra, Sept 30 2009

Where do Earthquakes Occur?Marshak

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Marshak

Where do earthquakes occur?A closer look Faults Listric faults (large landslides: gravitational collapse of volcanic edifices)Around VolcanosAnthropogenic Earthquakes Collapse of mine shafts Explosions

The Kursk DisasterOn August 12, 2000 the Russian Oscar-Class Submarine, Kursksank, killing all aboard What happened (and what does this haveto do with earthquakes)?Seismology (the study of earthquakes) gave clues about what happened.Russian officials later admitted that the disaster was the result of a faulty torpedo.Lesson: You Cant Hide Big Explosions

October 8, 2006North Korea Nuclear Test

Earthquakes come in all shapes and sizesMarshakRight vs. Left Lateral

INTENSITY: Amount of ground motion = Destructive PowerQualitative measurement depends on:MagnitudeDistance from focusDepth of focusRock typeBuilding type

MAGNITUDE: Quantitative measure of the amount of energy released. The Richter Scale is logarithmic.

Did you feel it?earthquakes.usgs.gov

The Richter Scale is Logarithmic

Press and Siever

How Big is Big?If the ENTIRE San Andreas Fault ruptured at once

Sheet1

Displacement (cm)Magnitude# of Hiroshima Bombs

507.571.54E+04

1007.783.09E+04

2007.986.18E+04

3008.099.26E+04

4008.181.23E+05

5008.241.54E+05

6008.291.85E+05

7008.342.16E+05

8008.382.47E+05

9008.412.78E+05

10008.443.09E+05

Percent Chance of a strong to great earthquake in the next 30 years along the San Andreas Fault

What happens during an earthquake?

MarshakTypes of deformation

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What happens during an earthquake?Marshak

May 24, 2006 Magnitude 5.4

MarshakSurface Rupture

What happens during an Earthquake?Kobe, JapanJanuary, 1995Magnitude 6.9

SEISMIC WAVESThe energy of an earthquake is dissipated by wavesP (primary) WavesCompressionalPush-pull motionTransmitted through liquidsS (secondary) WavesShearSide-to-side (and up-and-down) motionSlower than P wavesNot transmitted through liquidsSurface WavesRayleigh waves (rotational motion, think waves in water)Love waves (Side-to-side motion)

P WavesS WavesMarshak

Rayleigh WavesLove WavesMarshak

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*Earthquakes occur along plate boundaries, MOST OF THE TIME. However, earthquakes can occur anywhere.One of the interesting things is how in some places earthquakes deepen as you go away from plate boundaries These occur along subduction zones. Why?*************************