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# EarthSci 4 - Earthquake

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### EarthSci 4 - Earthquake

1. 1. Focus, Epicenter, and Fault
2. 2. Elastic Rebound Hypothesis
3. 3. Elastic Rebound Hypothesis
4. 4. Seismograph
5. 5. Seismogram
6. 6. Seismic Waves Paths Through the Earth
7. 7. Measuring EarthquakesP Waves - Are push-pull waves that push (compress) and pull (expand) in the direction that the waves travel - Travel through solids, liquids, and gases - Have the greatest velocity of all earthquake waves
8. 8. Measuring EarthquakesS Waves - Seismic waves that travel along Earth’s outer layer - Shake particles at right angles to the direction that they travel - Travel only through solids - Slower velocity than P waves
9. 9. Earth’s Interior Showing P and S Wave Paths
10. 10. Measuring EarthquakesLocating an Earthquake Earthquake Distance • The epicenter is located using the difference in the arrival times between P and S wave recordings, which are related to distance. Earthquake Direction • Travel-time graphs from three or more seismographs can be used to find the exact location of an earthquake epicenter. Earthquake Zones • About 95 percent of the major earthquakes occur in a few narrow zones.
11. 11. Locating an Earthquake
12. 12. Pusan Seismic Station S-P Interval = seconds
13. 13. Tokyo Seismic Station S-P Interval = seconds
14. 14. Akita Seismic Station S-P Interval = seconds
15. 15. Station S-P Interval Epicentral DistancePusan 60 seconds KMTokyo 50 seconds KMAkita 70 seconds KM
16. 16. RECORDING S-P EPICENTER STATION INTERVAL DISTANCE PUSAN 56 sec 549 km TOKYO 44 sec 434 km AIKITA 71 sec 697 km
17. 17. Location You Found Actual Location
18. 18. Measuring Earthquakes Richter Scale • Based on the amplitude of the largest seismic wave • Each unit of Richter magnitude equates to roughly a 32-fold energy increase • Does not estimate adequately the size of very large earthquakes
19. 19. Measuring Earthquakes Modified Mercalli • scales measures how people feel and react to the shaking of an earthquake. • It is a relative scale, because people experience different amounts of shaking in different places. • It is based on a series of key responses such as people awakening, the movement of furniture, and damage to structures.
20. 20. Earthquake Magnitudes
21. 21. Destruction from Earthquakes Seismic Vibrations  Liquefaction • Saturated material turns fluid • Underground objects may float to surface
22. 22. Tsunami
23. 23. Tsunami Cause of Tsunamis • A tsunami triggered by an earthquake occurs where a slab of the ocean floor is displaced vertically along a fault. • A tsunami also can occur when the vibration of a quake sets an underwater landslide into motion. • Tsunami is the Japanese word for “seismic sea wave.”
24. 24. Destruction from Earthquakes  Landslides • With many earthquakes, the greatest damage to structures is from landslides and ground subsidence, or the sinking of the ground triggered by vibrations.  Fire • In the San Francisco earthquake of 1906, most of the destruction was caused by fires that started when gas and electrical lines were cut.
25. 25. Predicting Earthquakes Short-Range Predictions • So far, methods for short-range predictions of earthquakes have not been successful. Long-Range Forecasts • Scientists don’t yet understand enough about how and where earthquakes will occur to make accurate long-term predictions. • A seismic gap is an area along a fault where there has not been any earthquake activity for a long period of time.