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Chapter 8 Earthquakes

Chapter 8 Earthquakes. San Francisco-1989. 1994- Northridge, CA. Section 8-1. What causes Earthquakes?. Stress of plates moving causes rock to bend and stretch.

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Chapter 8 Earthquakes

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  1. Chapter 8 Earthquakes San Francisco-1989 1994- Northridge, CA

  2. Section 8-1 What causes Earthquakes? Stress of plates moving causes rock to bend and stretch. Rocks reach their elastic limit and break, causing a sudden movement along a fault. During elastic rebound, energy is released. The energy released by the breaking of rock along a fault causes an earthquake

  3. Elastic rebound

  4. Where do Earthquakes occur? • Most occur along plate boundaries. • Along fault systems, some which can be far away from plate boundaries. • Around actively erupting volcanoes.

  5. Earthquakes in Last 30 Days Worldwide

  6. Earthquakes in the last week.

  7. PA eq’s

  8. Types of Faults Normal Fault-tension pulls rocks apart

  9. Fault Video

  10. Reverse Fault-compression pushes rock, one piece is forced up and over another.

  11. Strike-slip Fault-friction from shearing force builds up and rocks move when elastic limit is reached.

  12. Seismic waves

  13. Focus/Epicenter

  14. Types of Seismic Waves Primary (P-waves)- fastest of waves, travel at 6 km per second in an accordion-like motion. Weakest wave Secondary (S-waves)- travel half the speed of P-waves (3 km per second), move in a side to side motion. Stronger than P waves Surface (L-waves)- slowest of waves, move in a wave-like motion, strongest, cause the most destruction in an EQ

  15. Earthquakes are detected by a device called a seismograph Seismograph Seismogram Seismogram- paper record of EQ shaking. • An analysis of a seismogram tells seismologists 2 things: • How powerful the Earthquake is. • How far away the epicenter of the EQ is.

  16. Seismogram

  17. Finding Epicenter • Use P-wave arrival times • Use S-P lag times 3 Times are needed to pinpoint epicenter of EQ

  18. 8-2 EQ Measurement How do seismologists calculate the magnitude of an EQ? Mercalli Scale- old method of measuring EQ’s by damage caused. Not accurate due to building strengths in different areas. Richter Scale- measures EQ’s by describing how much energy is released by the EQ.

  19. How to find Richter Value Scale is from 0.1 to 9+ For every increase of 1.0 on Richter scale, 100 times more energy is released. 6.0 quake is 10,000 times stronger than a 4.0 Amplitude and Distance to find the Richter Value Get info from the seismogram!

  20. Predicting EQ’s Very difficult to predict actual day, more on time span. 1. Creep meter- measures movement by tying a wire across fault to measure movement 2. Lasers- line up laser and mirror on opposite sides of fault 3. Seismic gap- looks for areas that are building up stress along fault. 4. Satellite observations- use of GPS to monitor movement. SMALL MOVEMENT ALONG A FAULT CAN LEAD TO LARGE EARTHQUAKES.

  21. Structures are strongest when they are built on BEDROCK. Soft Earth leads to LIQUEFACTION.

  22. Base Isolators and Cross-bracingbest ways to strengthen buildings

  23. EQ Safety EQ Preparation: What to do during and after EQ:

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