Done by: DESHER TROTMAN
Definition: An earthquake is a sudden tremor or movement of the earth’s crust, which originates naturally at or below the Earth’s surface. They can occur from fault lines where tectonic plates meet or from volcanic activity. Earthquakes are very common in areas of volcanic activity where they either proceed or accompany eruptions. Earthquakes caused by volcanic eruptions are rare since all volcanoes are not prone to violent eruptions. When two plates meet the rocks are compressed and the tension builds up even if one plate is descending. Eventually a point comes where the strain in the rocks is too much for the structure to maintain and the rock layers move suddenly to relieve the tension. The release in tension is enormous and radiates as “shock waves” or seismic waves that can create fault lines. Earthquake has enormous destructive power, not just on land, but undersea they create giant tidal waves called tsunamis.
The epicenter is the point on the earth’s surface that is directly above the hypocenter or focus, the point where an earthquake or underground explosion originates. Hypocenter/ focus site of an earthquake.
The position where the strain energy stored in the rock is first released. Seismic waves:
Are waves of energy that travel through the earth.
The strength of earth quakes can either be measured using the Rictor Scale or Mercalli Scale. The rictor scale is based on shock wave acceleration and energy. * It is a logarithmic scale, meaning an increase in 1 unit means 10 times more powerful. Mercalli scale is based on a succession of increasingly dramatic observed events. * It was devised before Richter’s scale
| Mercalli Scale
| only detected by seismometers, very sensitive people
| feels like a heavy truck passing
| felt by people walking, most sleepers wakened
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