An earthquake is caused by the movement of lithospheric plates inside the surface of the Earth. Because these plates move, the surface of the Earth vibrates. The vibrations can travel all around the Earth. Anatomy of an Earthquake is discussed below
Anatomy of an Earthquake
- The place in the Earth’s crust where the movement first starts is called focus.
- The place on the surface above the focus is called epicentre.
- It is from the epicentre that vibrations in the form of waves travel outwards. These are known as seismic waves.
- The greatest damage and destruction to human life and property occur at places which are closest to the epicentre. The strength of the earthquake decreases as it moves away from the epicentre.
Earthquake waves are classified into three types. These are
- P waves: These are known as primary waves. They pass through solids, liquids and gases. These are the first earthquake waves which can be recorded on a seismogram.
- S waves: These waves travel through the Earth’s interior but cannot be transmitted by liquids. They are recorded on a seismograph after the P waves.
- L waves: They are long waves and are recorded after the P and S waves. L waves may be further classified into Love waves and Rayleigh waves.
The rise and fall of seawater because of the gravitational forces of the Sun and the Moon are called tides. Sea waves produced by tides are known as tidal waves. Read more