FOCUS AND EPICENTRE

The place of origin of an earthquake inside the earth is called its focus. The shock waves travel in all directions from the focus. On the earth’s surface, the shaking is strongest near the epicenter.

There are several types of earthquakes which affect different parts of the world at different times. Some of the common types of earthquakes are briefly described.

Tectonic Earthquakes- There are the most common earthquakes and

generated by sliding of rocks along a fault plane.

Volcanic Earthquakes- As the name indicates these earthquakes are caused

by volcanic eruptions and are quite devastating. However, these are confined to areas of active volcanoes.

Collapse Earthquakes- In areas of intense mining activity, often the roofs

of underground mines collapse and minor tremors take place. These are called collapse earthquakes.

Explosion Earthquakes- When a chemical or nuclear explosion takes

place, ground shaking occurs and an earthquake is known as explosion earthquakes.

Reservoir induced Earthquakes- Such earthquakes are caused by the pressure of water collection in large reservoir. The koyna earthquake was cause by koyna reservoir.

Measuring Earthquakes- The earthquakes are measured in terms of their magnitude and intensity.

 The earthquakes magnitude is related to the energy released during the quake and is recorded by an instruments called Seismograph. It is measured on Richter scale. This scale was developed by Charles Francis Richter. The magnitude is expressed in absolute numbers, 0-10.