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Features of Earthquakes

This article explores the features of earthquakes, focusing on the origin and types of seismic waves. It explains how rocks become trapped at faults, leading to stress that ultimately releases energy at the focus. We detail the three main types of seismic waves—Primary (P-waves), Secondary (S-waves), and Surface waves—highlighting their movement and destructive potential. Additionally, we discuss the process of locating an earthquake's epicenter using seismographs and outline the Earth's structure, including the crust, mantle, and core, along with the shadow zone for seismic waves.

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Features of Earthquakes

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  1. Features of Earthquakes

  2. 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. 3 types of seismic waves • Primary • Secondary • Surface

  4. Primary or P-waves • Particles in rocks move back and forth in same direction that wave is traveling • Fastest

  5. Secondary or S-waves • Particles in rocks move at right angles to direction wave is traveling • Slower

  6. Surface Waves • Particles in rocks move in a backward rolling motion & side to side swaying • Slowest • Most destructive

  7. Epicenter • Focus

  8. 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.

  9. Seismograph

  10. Basic Structure of Earth • Crust • Upper mantle • Lower mantle • Outer core • Inner core

  11. Crust • Outermost layer • Thickness varies 5 -60 km • More silicon & aluminum • Less magnesium & iron • Less dense than mantle

  12. Upper Mantle • Contains the asthenosphere • Weak rock flows slowly

  13. Lower mantle • Made of silicon, oxygen, magnesium, & iron

  14. Outer Core • Liquid made mostly of iron

  15. Inner Core • Solid • Dense • Mostly iron with nickel, oxygen, silicon,& sulfur • Pressure keeps it solid

  16. 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

  17. Moho • Boundary between crust and upper mantle (Mohorovicic discontinuity)

  18. 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

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