Features of Earthquakes
Feb 22, 2016
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