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| Monday, 27 December 2004 |
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An earthquake is a sudden movement of the Earth, caused by the abrupt release of strain that has accumulated over a long time. Earthquakes beneath the ocean floor sometimes generate immense sea waves or tsunamis ("huge wave" in Japanese). These waves travel across the ocean at speeds as great as 960 kilometres per hour and may be 15 meters high or higher by the time they reach the shore. The vibrations produced by earthquakes are detected, recorded, and measured by instruments call seismographs. The Richter Scale, named after Dr. Charles F. Richter of the California Institute of Technology, is the best known scale for measuring the magnitude of earthquakes. The scale is logarithmic so that a recording of 7, for example, indicates a disturbance with ground motion 10 times as large as a recording of 6. Earthquakes with a Richter value of 6 or more are commonly considered major; great earthquakes have magnitude of 8 or more on the Richter scale. Yesterday's earthquake off the west coast of Northern Sumatra at 3.298 N, 95.779 E (at a depth of 6.2 miles below sea level) had a magnitude of 8.9 on the Richter scale. The earthquake occurred at 00:58:50 hours GMT (06:58 a.m. Sri Lanka standard time) with a magnitude of 8.9 on Richter scale. This is the strongest earthquake recorded anywhere in the world for the last 50 years. It is the fifth strongest since 1900. |
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