Download - Features of Earthquakes
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Features of Earthquakes
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Origin of Seismic WavesMoving rocks get caught on each other at faults Stress builds up until elastic limit is passed Built-up energy is released at the focus Seismic waves are produced & travel outward
from focus
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3 types of seismic wavesPrimarySecondarySurface
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Primary or P-wavesParticles in rocks move back and forth in
same direction that wave is travelingFastest
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Secondary or S-wavesParticles in rocks move at right angles to
direction wave is travelingSlower
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Surface WavesParticles in rocks move in a backward rolling
motion & side to side swaying SlowestMost destructive
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EpicenterFocus
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Locating the epicenterSeismologists take seismograms from 3
different seismograph locations. They use these to determine the distance to
the epicenter of each station. Then they draw a circle around each station
with the distance as a radius. Point where all 3 intersect is the epicenter.
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Seismograph
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Basic Structure of EarthCrustUpper mantleLower mantleOuter coreInner core
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CrustOutermost layerThickness varies 5 -60 kmMore silicon & aluminumLess magnesium & ironLess dense than mantle
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Upper MantleContains the
asthenosphereWeak rock flows slowly
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Lower mantle
Made of silicon, oxygen, magnesium, & iron
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Outer Core
Liquid made mostly of iron
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Inner CoreSolidDenseMostly iron
with nickel, oxygen, silicon,& sulfur
Pressure keeps it solid
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Shadow Zonearea where NO seismic waves are detected
Primary are slowed and bent but not stopped
Secondary are not transmitted through the liquid outer core
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Moho
Boundary between crust and upper mantle (Mohorovicic discontinuity)
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Speed of Seismic WavesSeismic waves speed up through bottom of
crust & upper mantlePrimary and Secondary slow down in
asthenosphereGains speed in solid part of mantleSecondary stops in liquid outer corePrimary slow in outer core and speed up in
solid inner core