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EARTHQUAKES

Earthquakes are powerful vibrations caused by the breaking of rocks in the Earth's lithosphere, primarily involving the crust and upper mantle. When the elastic limit of rocks is surpassed, they break and produce seismic waves that radiate outwards. Key concepts include fault types (normal, thrust, and slip), the focus vs. epicenter distinction, and the various seismic waves: primary (P-waves), secondary (S-waves), and surface (L-waves). Understanding the Richter and Mercalli scales helps assess earthquake magnitude and damage, respectively, crucial for disaster response.

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EARTHQUAKES

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  1. EARTHQUAKES Shaking Crust

  2. EARTHQUAKES • Vibrations produced by breaking of lithosphere (crust & upper mantle) • Elastic limit = amount that rocks can stretch and bend • When surpassed rocks break & move • Seismic waves (vibrations) sent out in all directions

  3. Fault • Surface along which rocks move

  4. 3 Types of Faults • Normal Thrust/Reverse Slip Fault Fault Fault

  5. Focus vs. Epicenter • FOCUS – point below the surface where rocks actually break • EPICENTER – point on surface directly above the focus

  6. Primary Seismic Waves • P wave • Longitudinal wave – particles move parallel to wave direction • Fastest • Least destructive

  7. Secondary Seismic Waves • S wave • Transverse wave – particles move at right angles to wave direction • Slower than P waves • More destructive than P waves

  8. Surface Waves • L wave • Particles move in ellipses compared to wave direction • Slowest • Most destructive

  9. LAG TIME • LAG TIME = difference between first S wave and first P wave arrival at a seismic station • Longer lag time = further from the epicenter

  10. Time-Travel Graph • Compares distance from epicenter to lag time

  11. Seismograph Station-Locating an Epicenter • Triangulation-information from at least 3 seismic stations • Seismograph measures how much the surface of the earth moves • Draw 3 circles • Intersection = Epicenter

  12. Richter Scale- Measures the Magnitude • Measures amount of energy released, magnitude • OBJECTIVE scale • NOT influenced by other factors • Used to compare earthquakes • Increase of “1” = 10 times more energy released

  13. Mercalli Scale • Measures amount of damage done to man-made structures • SUBJECTIVE scale • Influenced by many factors (height of buildings, age, how built, etc. . .) • Used to determine amount of $$$ for aid

  14. San Andreas Fault- edge of the Pacific plate is slipping past the North American plate

  15. San Andreas Fault

  16. San Andreas Earthquake http://earthquake.usgs.gov/regional/nca/1906/18april/index.php

  17. San Andreas Earthquake http://earthquake.usgs.gov/regional/nca/1906/18april/index.php

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