An earthquake is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth’s lithosphere that creates seismic waves. Earthquakes can range in size from those that are so weak that they cannot be felt to those violent enough to propel objects and people into the air, and wreak destruction across entire cities. The seismicity or seismic activity is an area, is the frequency, type, and size of earthquakes experienced over a period of time. The word tremor is also used for non-earthquake seismic rumbling.
At the Earth’s surface, earthquakes manifest themselves by shaking and displacing or disrupting the ground. When the epicenter of a large earthquake is located offshore, the seabed may be displaced sufficiently to cause a tsunami. Earthquakes can also trigger landslides and occasionally, volcanic activity.
In its most general sense, the word earthquake is used to describe any seismic event—whether natural or caused by humans—that generates seismic waves. Earthquakes are caused mostly by rupture of geological faults but also by other events such as volcanic activity, landslides, mine blasts, and nuclear tests. An earthquake’s point of initial rupture is called its hypocenter or focus. The epicenter is the point at ground level directly above the hypocenter.
Effects of an Earthquake
- Ground shaking: Surface waves that are near the epicenter are responsible for the earthquake. The intensity of ground shaking depends on the duration, local geology, and distance.
- Damage to a man-made structure.
- An outbreak of fire and spilling of hazardous chemicals.
When an earthquake occurs, it releases waves of energy, which are known as Seismic waves. It is like the ripples created in water if you throw a stone in it. Seismic waves are like those ripples which can travel through the inside of the earth, as well as on the surface.
Surface waves are those waves that travel on the surface of the earth. The destruction caused by earthquakes is primarily done by S waves and P waves.
- S waves: They called secondary waves and shear waves, which are the second waves to hit the seismographs. They are transverse waves, which means that the motion is perpendicular to the direction of wave propagation. S waves can only travel through solids and scientists have been successful to map the interior of the earth by studying the routes of these waves.
- P waves or Primary waves: They are the first waves to hit the seismographs when an earthquake strikes. They are longitudinal waves which means that the direction of motion and propagation are the same.
Difference between p waves and s waves
|P waves||S waves|
|P waves are the first wave to hit the earth’s surface.||These arrive after P waves.|
|P waves travel in the speed range of 1.5-13 km/s.||These waves are almost 1.7 times slower than P waves.|
|These waves travel in a linear direction.||They travel in a transversal direction.|
|These waves can travel through solid, liquid, and gas.||These waves travel through only solids.|