Earthquakes
When forces deep in the Earth push the rigid crust
beyond endurance, the rocks can no longer take the
strain, rupturing and shearing in a massive burst of energy.
The result is an earthquake that can lay whole cities flat.
`````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````` |
 |
Causes of Earthquakes: Earthquakes are caused when tension is released from the rocks in the Earth's crust and upper mantle. This tension is due to friction between what scientists believe are large 'plates' floating on magma on the Earth's surface. Sometimes earthquakes happen when the rocks in the earth's crust bend and break. This causes shock waves to travel on the earth's surface, resulting in widespread destruction.
`````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````` |
 |
Plate Tectonics:
The layers of the earth Scientists believe that the earth is made up of four main layers. The outermost layer being the crust, then the mantle, the outer core and at the centre of the earth the inner core. The crust is made up of hard rock, mainly granite. The mantle is mainly molten lava on which the crust is floating. The core is mostly iron, with the outer core being liquid and the inner being solid. The mantle is continually moving; this is called convection. It is also believed that the earth is divided into more than a dozen plates, which are floating on the mantle. This theory is called plate tectonics . The plates often rub together, pull apart, collide or dive under one another. These movements cause earthquakes and also volcanoes.
`````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````` |
 |
The Richter Scale: The Richter scale is a scale designed by A. Richter to measure the strength or intensity of the shock waves produced by an earthquake. The scale is measured in steps from one upward. Each successive unit is ten times more powerful than the one before. Therefore an earthquake that measures 7.0 on the Richter scale is 1000 times more powerful than an earthquake measuring 4.0. Little damage is done by an earthquake below 4.0; an earthquake of 7.0, however, would cause widespread disaster.
`````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````` |
 |
Earthquake Occurrence: The original scale for measuring the severity of earthquakes was compiled by the Italian Seismologist, Guiseppe Mercalli, in1902. It has gone through a number of revisions since then. The Mercalli Scale relies on how much damage is caused by an earthquake.
Currently it runs as follows:
`````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````` |
 |
