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Earthquakes

Earthquakes. What is an Earthquake?. Earthquake-- Occur when rocks under stress shift along a fault (energy released) Fault — break in rock where one block moves relative to another. Let’s Build a Fault Model!. Damage from Northridge Earthquake in Southern California--1994.

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Earthquakes

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  1. Earthquakes

  2. What is an Earthquake? • Earthquake--Occur when rocks under stress shift along a fault (energy released) • Fault—break in rock where one block moves relative to another

  3. Let’s Build a Fault Model!

  4. Damage from Northridge Earthquake in Southern California--1994

  5. Anatomy of an Earthquake • Focus--1st motion of earthquake in Earth, along fault • Epicenter—point on Earth’s surface directly above focus • 90% of continental earthquakes have shallow focus—most damaging

  6. Parts of an Earthquake

  7. Elastic Rebound Elastic Rebound—sudden return of deformed rock to undeformed shape Elastic rebound causes earthquakes

  8. Fence offset due to Elastic Rebound

  9. Seismic Waves • When rocks on a fault move, they release energy as seismic waves • Seismic waves travel outward from the focus in all directions

  10. Body wave—seismic wave that travels thru a medium • two types:P-wave &S-wave

  11. Seismic Waves • P (primary) waves are the fastest & travel thru solids, liquids, & gases

  12. Seismic Waves • S (secondary) waves are 2nd fastest & travel thru solids only. Although slower they can cause the most damage

  13. Seismic Waves Surface wave— a seismic wave that travels along surface of medium. These are S & P waves that reach the surface & can cause greatest damage

  14. Water Wave and Slinky Activities!

  15. WAYS TO MEASURE AN EARTHQUAKE • There are two major scales to measure an earthquake: • Mercalli Scale: measures earthquake intensity (by amount of damage caused) • Richter Scale: measures earthquake magnitude (strength)

  16. Studying Earthquakes • Seismology—study of earthquakes & seismic waves • Seismograph—records vibrations in ground • Seismogram—tracing of EQ motion, recorded by seismograph

  17. Bill Nye on the Richter Scalehttp://www.youtube.com/watch?v=1qbg7orb1lcBill Nye on WavesEarthquake recording station/seismograph cliphttp://www.youtube.com/watch?v=dx4OqT0PYnU&lr=1

  18. SEISMOGRAM • Order of recording: P-waves, S- waves, then surface waves • Shows S-P lag time

  19. P-Wave S-Wave S-Wave S-Wave • To find S-P lag time, subtract where the P wave starts from where the S wave starts (S-P = Lag Time)

  20. What is S-P lag time for El Paso,TX? • 28 sec – 0 sec = 28 sec lag time What is S-P lag time for San Francisco, CA? • 120 sec – 0 sec = 120 sec lag time What is S-P lag time for Seattle, WA? • 165 sec – 0 sec = 165 sec lag time Which city is closest to the epicenter? • The city with the shortest lag time is closest to the epicenter, so it’s El Paso, TX

  21. Locating Earthquakes Through Triangulation • S-P lag times are analyzed to find the epicenter of Earthquakes using 3 stations • Why 3 stations? • Because all we know is distance, so it takes 3 circles to narrow it down to one point Epicenter

  22. Let’s stop here and practice finding S P lag time

  23. Fault Zones • Fault zone—region w/ lots of faults that typically form at plate boundaries • Fault zones and earthquakes can occur away from plate boundaries as well

  24. Fault Zones—New Madrid • New Madrid fault line—New Madrid, MO—120 miles southward on I-55 • 1811/1812—most widely felt series of E.Q. in U.S. history (2000+) • Five were 8.0+ • Ancient fault zone deep in crust of Mississippi River region

  25. Tsunamis • Tsunami—giant ocean wave that forms after volcanic eruption, submarine earthquake or landslide • May form when ocean floor rises due to earthquake Tsunami animation http://embc.gov.bc.ca/em/tsunamis/causes_2.htm

  26. Japan’s Tsunami Before and After…(Google Earth)

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