What Causes Earthquakes?


Recent events in Haiti, have shown us the vast destruction and lost of life that a major earthquake causes. The 2010 Haiti earthquake was a catastrophic magnitude 7.0 Mw earthquake. Its epicenter was near the town of Léogâne, approximately 25 km (16 miles) west of Port-au-Prince, Haiti's capital. The earthquake occurred at 16:53 local time (21:53 UTC) on Tuesday, 12 January 2010. By 24 January, at least 52 aftershocks measuring 4.5 or greater had been recorded. An estimated three million people were affected by the quake; news states that 200,000 people have been identified as dead and that an estimated 300,000 injured have been treated so far. It is also estimated that 250,000 residences and 30,000 comercial buildings have collapsed or severely damaged.
Most earthquakes result from the strain that builds up at tectonic plate boundaries. More than 3 million earthquakes occur each year. Most of these are too small to be noticeable. Each year, however, a number of powerful earthquakes occur (Haiti's being one). Earthquakes are measured using intensity and magnitude scales. The Mercalli scale measures the intensity of an earthquake based on the reports of people who experienced or observed the amount of destruction it caused. The most dependable measurements of earthquakes, however, are made with seismographs. Seismographic records of earthquakes have established magnitude scales. The Richter scale is one such magnitude scale. A seismograph records the magnitude of an earthquake and the time the seismic waves arrive. Seismologists use the difference in the speeds of P- and S-waves to locate the epicenter of earthquakes.


Homework #2: Due Thursday, February 11, 2010

Review Book: read pages 56-58;
Textbook: read chapter 10.1, pages 214-216; do section review questions 1-5, page 216.

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