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Selasa, 28 Februari 2012

How earthquakes happen




Earthquake is one of the most destroying natural disasters. Unluckily it often happens in several regions. Recently a horrible earthquake has shaken West Sumatra. It has brought great damages. Why did it occur? Do you know how an earthquake happens?

Earthquakes are usually caused when rock underground suddenly breaks along a fault. This sudden release of energy causes the seismic waves. It make the ground shake. When two blocks of rock or two plates are rubbing against each other, they stick a little. They don't just slide smoothly. The rocks are still pushing against each other, but not moving. After a while, the rocks break because of all the pressure that's built up. When the rocks break, the earthquake occurs.

During the earthquake and afterward, the plates or blocks of rock start moving, and they continue to move until they get stuck again. The spot underground where the rock breaks is called the focus of the earthquake. The place right above the focus is called the epicenter of the earthquake.


Release of Power

The cause of earthquakes is most often due to a shift in the earth's plates (tectonics). Tectonic earthquake occurred due to movement of earth plates large and small that shape the earth's crust. Earth's crust is hard to be critical (soft) and finally moving.


The theory of "Plate Tectonics" explains, the earth consists of several layers of rock. Most of the area of the crust it will drift and float in layers like the snow. Stir gently so that the layer-break berpecah and collide with each other. Most earthquakes occur at the boundary between tectonic plates forming Earth's crust, such as the Pacific rim.

Activity or area of subduction zone plate collision plays an almost 50 percent of the seismic event that occurred. Subduction zone activity is concentrated in an area called the circle of fire (ring of fire), a narrow band around 38 600 km length. The length of this ribbon stretching from New Zealand-Indonesia-Japan-to South America.


What about the tsunami ?

tsunami


The tsunami itself is a Japanese term. Stating a sea wave caused by tectonic earthquakes on the seabed. Tsunami magnitude that occurred in Indonesia ranges from 1.5 to 4.5 Imamura scale, with a high maximum tsunami wave that reached the coast ranges from 4-24 meters and reach of the waves to the mainland ranged from 50 to 200 meters from the coastline.


Based on the earthquake catalog (1629 - 2002) never happened Tsunami in Indonesia as much as 109 times, which is 1 times the result of landslides (landslide), 9 times due to volcanoes and 98 times the result of tectonic earthquake.
Tsunamis usually occur within 3-60 minutes after the quake. Marked by the reflux of sea water and flying dozens maybe even hundreds of sea birds to the mainland. They also smell of salt.
Not all of tectonic earthquake on the ocean floor cause tsunamis. Many factors cause. As the strength and depth of the epicenter. Therefore, if within the period of one hour after the earthquake, you do not see the signs as above
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