Earthquake is a sudden violent movement of the earth’s surface.It occurs when a lot of energy, stored within earth,is released.This energy is transmitted to the surface of the earth by earthquake waves.The study of earthquakes is called seismology.The scientists who study earthquakes are called seismologists.Seismographs are the machines that record the earthquakes. The point within the earth where an earthquake originates is called the focus.The point on the earth’s surface directly above the focus is called epicenter. The theory is that the earth’s crust is made of tectonic plates.The points where these meet are called the faults.Faults are basically cracks between these plates on the earth surface or within the earth.The surface between the two sides of a fault lies in a plain.Sometime, the fault plain dips into the ground.The rock hanging over the dipping fault plain slips downward into the ground.It is called a normal fault.When the hanging wall slips upward,it is called reverse fault.Both these faults produce vertical displacements.Sometime the tectonic plates slide horizontally in the fault plain.Such a slip in the fault plain produces horizontal displacements.The faults where such a movement takes place are called strike-slip faults. The sudden movement of rocks along a fault causes vibrations.These vibrations transmit energy through the earth in the form of waves.These waves are called seismic waves.They are classified into four types.They are p(primary) wave,s (secondary) waves,love waves and rayleigh waves.P and s waves are produced within the earth.The other two waves are produced along the surface of the earth. The p wave travels at the highest speed.It can be transmitted by both solid and liquid materials.
With a p wave the transmitting rocks are alternately compressed and expanded. The s wave travels only through solid material within the earth.The s waves are known as shearing waves.They move the ground back and forth. Love and rayleigh waves travel from the epicenter along the surface of the earth.These waves also cause damage to structures,as they shake the ground underneath the foundations of buildings and other structures. Earthquake result in landslides and other soil movement.These events cause an enormous loss of property and life.Secondary damage of the earthquakes includes economic loss, diseases , lack of food and dearth of clean water. Seismologists try to predict earthquakes.This prediction may include a specific time,place and size of the expected earthquake.In this regard, the scientists take help from the previous record of earthquakes.This helps them to determine the expected repitation of earthquakes.In spite of all this, the prediction of earthquake should always be taken to be uncertain.The occurrence should always be regarded as a chance event. The sudden movements of rocks along a fault causes vibrations.These vibrations transmit energy through the earth in the form of waves.These waves are called seismic waves. The theory is that the earth crust is made of tectonic plates.These plates are lying side by side.The points where these plates meet are called faults.Faults are basically cracks between these plates on the earth surface or within the earth.The surface between two sides of a fault lies in a plain.Sometimes,the fault plain dips into the ground.The rock hanging over the dipping fault plain slips downward into the ground.It is called a normal fault.When the hanging wall slips upward,it is called a reverse fault.Both these faults produce vertical displacements.Sometimes the tectonic plates slide horizontally in the fault plain.Such a slip in the fault plain produces horizontal displacements.The faults where such a movement takes place are called strike-slip faults.
