Features of Earthquakes

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

3 types of seismic wavesPrimarySecondarySurface

Primary or P-wavesParticles in rocks move back and forth in

same direction that wave is travelingFastest

Secondary or S-wavesParticles in rocks move at right angles to

direction wave is travelingSlower

Surface WavesParticles in rocks move in a backward rolling

motion & side to side swaying SlowestMost destructive

EpicenterFocus

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.

Seismograph

Basic Structure of EarthCrustUpper mantleLower mantleOuter coreInner core

CrustOutermost layerThickness varies 5 -60 kmMore silicon & aluminumLess magnesium & ironLess dense than mantle

Upper MantleContains the

asthenosphereWeak rock flows slowly

Lower mantle

Made of silicon, oxygen, magnesium, & iron

Outer Core

Liquid made mostly of iron

Inner CoreSolidDenseMostly iron

with nickel, oxygen, silicon,& sulfur

Pressure keeps it solid

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

Moho

Boundary between crust and upper mantle (Mohorovicic discontinuity)

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