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Features of Earthquakes. Origin of Seismic Waves. Moving rocks get caught on each other at faults Stress builds up until elastic limit is passed Built-up energy is released at the focus

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origin of seismic waves
Origin of Seismic Waves
  • Moving 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 waves
3 types of seismic waves
  • Primary
  • Secondary
  • Surface
primary or p waves
Primary or P-waves
  • Particles in rocks move back and forth in same direction that wave is traveling
  • Fastest
secondary or s waves
Secondary or S-waves
  • Particles in rocks move at right angles to direction wave is traveling
  • Slower
surface waves
Surface Waves
  • Particles in rocks move in a backward rolling motion & side to side swaying
  • Slowest
  • Most destructive
locating the epicenter
Locating the epicenter
  • Seismologists 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.
basic structure of earth
Basic Structure of Earth
  • Crust
  • Upper mantle
  • Lower mantle
  • Outer core
  • Inner core
  • Outermost layer
  • Thickness varies 5 -60 km
  • More silicon & aluminum
  • Less magnesium & iron
  • Less dense than mantle
upper mantle
Upper Mantle
  • Contains the asthenosphere
  • Weak rock flows slowly
lower mantle
Lower mantle
  • Made of silicon, oxygen, magnesium, & iron
outer core
Outer Core
  • Liquid made mostly of iron
inner core
Inner Core
  • Solid
  • Dense
  • Mostly iron with nickel, oxygen, silicon,& sulfur
  • Pressure keeps it solid
shadow zone
Shadow Zone
  • area where NO seismic waves are detected
  • Primary are slowed and bent but not stopped
  • Secondary are not transmitted through the liquid outer core
  • Boundary between crust and upper mantle (Mohorovicic discontinuity)
speed of seismic waves
Speed of Seismic Waves
  • Seismic waves speed up through bottom of crust & upper mantle
  • Primary and Secondary slow down in asthenosphere
  • Gains speed in solid part of mantle
  • Secondary stops in liquid outer core
  • Primary slow in outer core and speed up in solid inner core