Earthquakes

EarthquakesEarthquakes

Sudden movement of surface whenaccumulated strain along opposingsides of a fault is suddenly released.Rock stretches and snaps.Sudden movement of surface whenaccumulated strain along opposingsides of a fault is suddenly released.Rock stretches and snaps.

>90% boundaries>90% boundaries

greatest intensity at subduction zonesgreatest intensity at subduction zones

(also occur at transform boundaries andspreading boundaries)(also occur at transform boundaries andspreading boundaries)

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

Energy released as seismic wavesEnergy released as seismic waves

Vibrations generated by movementVibrations generated by movement

Waves travel along surface and throughearth:Waves travel along surface and throughearth:

Body waves: move through earthBody waves: move through earth

P and S wavesP and S waves

Surface Waves: move along surfaceSurface Waves: move along surface

Body WavesBody Waves

P waves:P waves:

PrimaryPrimary

Fast (3.5 miles per second)Fast (3.5 miles per second)

CompressionCompression

Push-pullPush-pull

Travel through liquids and solidsTravel through liquids and solids

Body wavesBody waves

S waves:S waves:

SecondarySecondary

Slower (1.5 miles per second)Slower (1.5 miles per second)

Shear wavesShear waves

Displace material perpendicular to line of travelDisplace material perpendicular to line of travel

Do not travel through liquidsDo not travel through liquids

Surface WavesSurface Waves

Most destructiveMost destructive

Slower than P or SSlower than P or S

Focus: point of initiation of movement; incrust or upper mantleFocus: point of initiation of movement; incrust or upper mantle

Epicenter: point on surface above thefocus; geographic centerEpicenter: point on surface above thefocus; geographic center

Richter scaleRichter scale

Instrumental scale showing energyreleased during quake; based onamplitude of seismic wavesInstrumental scale showing energyreleased during quake; based onamplitude of seismic waves

Measured by seismographMeasured by seismograph

Logarithmic ; 2 - 10Logarithmic ; 2 - 10

seismographseismograph

Pendulum connected to recorderPendulum connected to recorder

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

Loma Prieta, California, 1989magnitude 7.1Loma Prieta, California, 1989magnitude 7.1

Mercalli ScaleMercalli Scale

Based on observed amount of damage tobuildings and effects felt by peopleBased on observed amount of damage tobuildings and effects felt by people

I - XIII - XII

Moment Magnitude scaleMoment Magnitude scale

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