Earthquake & Wave Types ( Primary, Secondary & Surface )

Earthquake

• The sudden tremors or sharing of the earth’s crust is called earthquake.
• Most of the earth quakes in the world are caused by the movements of the plates.
• Seismology is the study of earthquake.
• Richter scale is the instrument to measure the intensity of an earthquake.
• The point of origin of earthquake is called seismic focus.
• Most of the earthquakes originate at the depth of 50-100km inside the earth.
• The point of the earth surface vertically above the centre is called Epicenter.

Types of Earthquake

Mainly four types of Earthquake are there

Tectonic Earthquake

A tectonic earthquake is one that occurs when the earth's crust breaks due to geological forces on rocks and adjoining plates that cause physical and chemical changes.

Volcanic Earthquake

A volcanic earthquake is any earthquake that results from tectonic forces which occur in conjunction with volcanic activity.

Collapse Earthquake

Collapse earthquakes are small earthquakes in underground caverns and mines that are caused by seismic waves produced from the explosion of rock on the surface.

Explosion Earthquake

An explosion earthquake is an earthquake that is the result of the detonation of a nuclear and/or chemical device. This type is also called artificial or man-made. This type of earthquakes can be easily predicted & controlled.

Seismic waves

When Earthquake occurs some seismic waves are generated and travel through the Earth's layers. These are of mainly three types Primary, Secondary & Surface or Long waves.

Primary waves ( P-waves )

These are compressional waves & longitudinal in nature. These waves can travel through any type of materials solids, liquids and gases. Comparatively it travels with the fastest velocity and reaches the seismograph stations first and hence the name 'Primary'.

Secondary waves ( S-waves )

These waves travel through solids but do not travel through fluids because they are transverse in nature and fluids do not support shear stresses. Thus cannot pass through core. There speed is second to the Primary waves & reaches the seismograph stations after the Primary waves & hence the name 'Secondary'.

Surface or long waves ( L-waves )

These waves ravel on earth’s surface and causes maximum destruction because of large amplitude & long duration. Their velocity is lower than that of body waves (P & S) and hence recorded after the p and s waves.