Earthquakes

Earthquakes

» The sudden tremors or shaking of the earth's crust is called an earthquake. When a part of the earth's surface moves backward and forward or up and down, the earth's surface 'quakes', and these are called the 'earthquake'.
» The earth's crust is made up of different parts of various sizes. They are called plates.
» Most of the earthquakes in the world are caused by the movements of the plates.
» 'Seismology' the special branch of Geology, Itdeals with the study of earthquake.
» 'Richter scale' and 'Mercalli scale' are the instruments to measure/record the magnitude and the intensity of an earthquake respectively.

Seismic Waves

» The place where the seismic waves originate beneath the earth's surface is called the focus of the earthquake.
» The epicenter is that point on the ground surface which is closest to the focus. Seismic waves are recorded on the seismograph.
» Seismic waves are mainly of three types :
1. Primary waves
2. Secondary waves
3. Surface or Long waves

The earthquake zones in India

» The Indian plate is moving from south to north. That is why there are earthquakes in the Himalayan region.
» Earthquakes occur in Assam, Arunachal Pradesh, Nagaland, Tripura, Manipur, Mizoram, Andaman and Nicobar Islands, Jammu and Kashmir, the north¬western region of Uttar Pradesh, the northern region of Bihar etc.
» During the last few years, there have been several earthquakes of varying intensities in Maharashtra and Gujarat.