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Earthquakes!

Earthquakes!. Most earthquakes occur at Plate Boundaries The deepest earthquakes occur at subduction boundaries. The focus of an earthquake is the source, or where it originates. The epicenter is the point on the Earth’s surface directly above the focus.

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Earthquakes!

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  1. Earthquakes!

  2. Most earthquakes occur at Plate Boundaries The deepest earthquakes occur at subduction boundaries

  3. The focus of an earthquake is the source, or where it originates. The epicenter is the point on the Earth’s surface directly above the focus.

  4. Seismographs are used to record the various types of seismic waves that are generated during an eathquake. (see picture above right in packet to see how one looks/works)

  5. Types of Seismic Waves • P- Waves (elastic) – push and pull the ground • Travel through solids, Liquids & gases • S-Waves (shear) – move the ground up and down. • Only travel through solids

  6. Types of Seismic Waves • L-waves (Rayleigh/Love waves)- rolling surface waves; arrive last • Only travel through solids

  7. Recording Earthquakes • Seismographs record results on seismograms • The difference in arrival times of p and s waves= lag time • Using lag time we can find the distance to the epicenter

  8. Recording Earthquakes The further away the seismograph station, the greater the lag time.

  9. Discussion/Answer in packet Which city is located farthest from the epicenter? (use picture at left in packet) What is the difference between arrival times of the first P and S waves in the seismogram above (in the packet)?

  10. Travel-Time Graphs • Used to record the distance (measured in km) from the recording center to the epicenter of an earthquake

  11. The difference in arrival times of p and s waves= lag time

  12. Discussion/Answer in Packet When the first P-wave arrives 4 minutes before the first S-wave, the earthquake occurred _________ km from the recording station.

  13. Locating an Epicenter Using seismograms from 3 record stations and a travel-time graph, we can establish the location of the earthquake _______________________.

  14. Discussion/answer in packet How far from the epicenter is each of these three cities?

  15. Discuss/Answer in packets Why do seismologists need to plot data from three recording centers?

  16. Recording Earthquakes • We need 3 seismograph stations to find the epicenter of an earthquake. • With one, it could be anywhere on the circle. • With two, it could be either two areas they touch. • With three, its where they all meet!

  17. Why plate boundaries?? This is where the crust is under stress and potential energy is stored.

  18. Magnitude • Measure of how much energy is released. • Richter scale is used to plot, from 1 – 10, how strong an earthquake is. • Each increase in 1 equals 10 times more energy released.

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