What is an Earthquake?
An Earthquake is a sudden trembling and shaking of Earth’s surface caused by the release of a huge amount of energy in lithosphere (crust+solid mantle). The release of energy within the earth’s lithosphere is caused, usually from the slipping of tectonic plates along a fault, creating seismic waves that travel outwards from the source/ focus. The other causes of the earthquakes may be volcanic eruption, faulting, and filling or emptying of aquifers. The energy that causes an earthquake is transferred from the Epicenter to the surface through seismic waves. Earthquakes may be of different intensities, ranging from those so weak they cannot be felt, to those violent enough to propel objects and people into the air, damage critical infrastructure, and wreak destruction across entire cities. The frequency, type, and intensity of the earthquakes experienced at a particular area for a specific period of time is known as the seismic activity of that particular area. The seismicity at a particular location in the Earth is the average rate of seismic energy release per unit volume.
While simplifying the definition, an earthquake is any kind of event on/in the Earth, which generates seismic waves. Moreover, when these seismic waves travel upward to the Earth’s surface bring about shaking and trembling on the surface, which is known as an Earthquake. The point where there is the origin of the Earthquake, is known as Hypocenter or Focus, while the point of Earth surface, which directly above the Hypocenter, is known as Epicenter.
Types of Seismic Wave (Earthquake Waves)
An earthquake generates seismic waves that penetrate the Earth as body waves (P & S) or travel as surface waves (Love and Rayleigh). Each wave has a characteristic speed and style of motion. The animations below illustrate both the propogation of the wave as well as the motion of particles as the wave passes.
Body Waves
P-Waves:
S-Waves:
Surface Waves
L-Waves:
R-Waves: