EarthquakesEarthquakes

Sudden movement of surface Sudden movement of surface when accumulated strain along when accumulated strain along opposing sides of a fault is opposing sides of a fault is suddenly released. Rock suddenly released. Rock stretches and snaps.stretches and snaps.

>90% boundaries>90% boundaries

greatest intensity at subduction greatest intensity at subduction zoneszones

(also occur at transform boundaries and (also occur at transform boundaries and spreading boundaries)spreading boundaries)

Displacement 1” – 20’Displacement 1” – 20’

Energy released as Energy released as seismic wavesseismic waves Vibrations generated by movementVibrations generated by movement

Waves travel along surface and Waves travel along surface and through earth:through earth:

Body wavesBody waves: move through earth: move through earth P and S wavesP and S waves

Surface WavesSurface Waves: move along surface: move along surface

Body WavesBody Waves

P waves:P waves:

PrimaryPrimary Fast (3.5 miles per second)Fast (3.5 miles per second) CompressionCompression

Push-pullPush-pull Travel through liquids and solidsTravel through liquids and solids

Body wavesBody waves

S wavesS waves::

SecondarySecondary Slower (1.5 miles per second)Slower (1.5 miles per second) Shear wavesShear waves

Displace material perpendicular to line of Displace material perpendicular to line of traveltravel

Do not travel through liquidsDo not travel through liquids

Surface WavesSurface Waves

Most destructiveMost destructive

Slower than P or SSlower than P or S

FocusFocus: point of initiation of : point of initiation of movement; in crust or upper mantlemovement; in crust or upper mantle

EpicenterEpicenter: point on surface above the : point on surface above the focus; geographic centerfocus; geographic center

Richter scaleRichter scale

Instrumental scale showing energy Instrumental scale showing energy released during quake; based on released during quake; based on amplitude of seismic wavesamplitude of seismic waves Measured by Measured by seismographseismograph

Logarithmic ; 2 - 10Logarithmic ; 2 - 10

seismographseismograph

Pendulum connected to recorderPendulum connected to recorder

Kobe, Japan 1995Kobe, Japan 1995magnitude 7.2magnitude 7.2

Loma Prieta, California, Loma Prieta, California, 19891989

magnitude 7.1magnitude 7.1

Mercalli ScaleMercalli Scale

Based on observed amount of Based on observed amount of damage to buildings and effects felt damage to buildings and effects felt by peopleby people

I - XIII - XII

Moment Magnitude scaleMoment Magnitude scale

Includes amount of movement along Includes amount of movement along fault, geology of substrate, size of fault, geology of substrate, size of failure areafailure area

TsunamisTsunamis

Seismic sea wavesSeismic sea waves

Caused by Caused by earthquake earthquake beneath ocean (or beneath ocean (or submarine submarine volcanoes or volcanoes or landslides)landslides)

Waves radiate in all directionsWaves radiate in all directions Can move across entire oceanCan move across entire ocean

1960 Chile earthquake caused tsunami in 1960 Chile earthquake caused tsunami in JapanJapan

Can cross Pacific in < 24 hoursCan cross Pacific in < 24 hours

Speed and amplitude depend on depth Speed and amplitude depend on depth of oceanof ocean 500 mph in deep ocean; low amplitude 500 mph in deep ocean; low amplitude

crestscrests 20-30 mph in shallow ocean, high amplitude20-30 mph in shallow ocean, high amplitude

Amplitude increases, wavelength decreases,

approaching shore.

213 km

23 km

10.6 km

4000 m

50 m 10 m

Tsunami, Dec. 26, 2004Tsunami, Dec. 26, 2004off western coast of northern Sumatraoff western coast of northern Sumatra

275,000 death toll275,000 death toll Magnitude 9.15 earthquakeMagnitude 9.15 earthquake Subduction of Austral-Indian beneath Eurasian plateSubduction of Austral-Indian beneath Eurasian plate 750 miles faultline slipped 50 feet750 miles faultline slipped 50 feet Slightly altered earth’s rotationSlightly altered earth’s rotation Raised sea level 0.1 mmRaised sea level 0.1 mm

Banda Aceh, IndonesiaBanda Aceh, Indonesia

Memorial slide show for tsunami Memorial slide show for tsunami victimsvictims