what is an earthquake ?
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Earthquake:
Earthquake is the sudden shaking of the aurface of the Earth. It is caused by the disturbance observed deep inside the Earth. Earthquakes may lead to destruction of life and property. Earthquakes also cause tsunamis and landslides. To understand how earthquake is caused, let us study the internal structure of the Earth.
Structure of the Earth
The Earth has three main layers core, mantle and crust. The aurface of the Earth where we live is known as the crust. The oceanic and continental crusts are the two parts that form the crust. The continental crust is generally older than the oceanic crust and consists of a number of moving plates that either collide with each other or pull apart from each other. Just below next layer is mantle. It is softer and denser than crust. The crust and the upper layer of the mantle are together known as the lithosphere. The lithosphere is divided into several large and small plates of rocks called the tectonic plates. These tectonic plates keep moving and sliding past each other and cause disasters like earthquakes.
How earthquakes occur:
The tectonic plates of the Earth are in a constant motion and are similar to the pieces of a jigsaw puzzle. When these plates move, they sometimes collide or slide past each other which causes the earthquake. The surface where they slip is called the fault plane (or the fault), Since the surfaces of these tectonic plates are rough, sometimes they get stuck while trying to move past each other. When the edges release themselves, the energy which got confined radiates outwards from the faults in the form of seismic waves. The place beneath the surface of the Earth where the earthquake starts is called the focus of the earthquake and the point on the surface of the Earth directly above the focus is called the epicentre of the earthquake. The intensity of an earthquake is maximum at the epicenter. In India, the areas most threatened by earthquake are Kashmir, western and central Himalayas, Rann of Kutch, Rajasthan and Indo-Gangetic plain.
Measuring Earthquakes:
Seismic waves generated during an earthquake are measured using an instrument called a seismograph. The science of studving about earthquakeis called seismology. A seismograph generates a series of lines, called a seismogram, that indicates the magnitude of an earthquake. These different magnitudes are measured using a scale known as the Richter scale. This scale was developed by Charles Richter in 1935 which indicates how mild or destructive an earthquake could be.
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