earthquakes

Earthquakes

Earthquakes are considered as one of the most common natural disasters. Earthquakes are not onldslides, also can be ind phenomena such as geological states, Earthquakes are and landslides, but also can be induced by human activities owing to mine blasts, nuclean experimentation, etc.

Types of Earthquakes

egion, there are three different types of earthquakes:

the geological formation of the particular

1. Tectonic earthquakes: Tectonic earthquakes are the most common and occur when the rocks in the earth's crust tend to break due to geological forces that are induced by the movement of tectonic plates.

2. Volcanic earthquakes: Earthquakes that occur in conjunction with volcanic activity is known as volcanic earthquakes.

3. Collapse earthquakes: Small earthquakes that occur in underground caverns and mines are known as collapse earthquakes

Earthquakes can also be categorised as follows:

1. Inter plate earthquake: Earthquakes that occur along the boundaries of the tectonic plates are called inter plate earthquake. This is most common form.

2. Intra plate earthquakes: Earthquakes that occur within a tectonic plate but are away from the plate boundaries called Intra plate earthquake. The 1993, Latur earthquake in India is an example of intra plate earthquake.

Focus and Epicentre of Earthquake

Earthquakes can occur on the earth's surface and down at a depth of about 700km. The point within the earth where the earthquake starts is known as focus. The energy that released is propagated as seismic wave to all directions from the focus. The epicentre is the point on the earth's surface that is directly above the focus.

Shaking and ground rupture are the main effects created by earthquakes. The severity of the local effects depends on the complex combination of the earthquake magnitude, the distance from the epicentre, and the local geological conditions which may amplify or reduce wave propagation. The severity of an earth quake is generally measured by its magnitude in Richter scale as shown below.

A comprehensive data of some important earthquakes are given in Table 1. The following anthropogenic activities may enhance the frequency of earthquakes.

1. Underground nuclear testing

2. Impoundment of huge quantity of water in the lake behind a big dam.