Group items tagged

An earthquake is what happens when two blocks of the earth suddenly slip past one another. The surface where they slip is called the fault or fault plane. The location below the earth’s surface where the earthquake starts is called the hypocenter, and the location directly above it on the surface of the earth is called

the epicente

How are earthquakes recorded? Earthquakes are recorded by instruments called seismographs. The recording they make is called a seismogram. (figure 4) The seismograph has a base that sets firmly in the ground, and a heavy weight that hangs free. When an earthquake causes the ground to shake, the base of the seismograph shakes too, but the hanging weight does not. Instead the spring or string that it is hanging from absorbs all the movement. The difference in position between the shaking part of the seismograph and the motionless part is what is recorded.

he huge waves moved quickly across the ocean before hitting land. The waves caused a huge amount of destruction to towns and resorts along the coast. Over 150,000 people were killed as the tsunami waves hit the coasts of Indonesia, Malaysia, Myanmar, Thailand, Bangladesh, Sri Lanka, India, and the east coast of Africa. There was very little time to sound alarms and get people away from the coast. The more you know about how the Earth works, the more you can keep yourself and others as safe as possible from natural disasters. We at Windows to the Universe would like to congratulate Tilly Smith, a 10-year-old British girl who used her knowledge about how tsunamis works to save 100 people during the event. Tilly learned about tsunamis at school two weeks before the tsunami hit where her family was vacationing in Phuket, Thailand. She saw the water drawing out quickly from the shore and remembered that this can happen before a tsunami wave hits the coast. Thanks to Tilly, her mother, and the hotel staff, everyone was cleared off the beach minutes before the wave arrived. Last modified May 21, 2008 by Lisa Gardiner.

The short answer is that earthquakes are caused by faulting, a sudden lateral or vertical movement of rock along a rupture (break) surface.     Here's the longer answer: The surface of the Earth is in continuous slow motion. This is plate tectonics--the motion of immense rigid plates at the surface of the Earth in response to flow of rock within the Earth. The plates cover the entire surface of the globe. Since they are all moving they rub against each other in some places (like the San Andreas Fault in California), sink beneath each other in others (like the Peru-Chile Trench along the western border of South America), or spread apart from each other (like the Mid-Atlantic Ridge). At such places the motion isn't smooth--the plates are stuck together at the edges but the rest of each plate is continuing to move, so the rocks along the edges are distorted (what we call "strain"). As the motion continues, the strain builds up to the point where the rock cannot withstand any more bending. With a lurch, the rock breaks and the two sides move. An earthquake is the shaking that radiates out from the breaking rock.