Epicentre: It is the point on the surface of the earth, vertically above the place of origin (hypocenter) of an earthquake. This point is expressed by its geographical Coordinates in terms of latitude and longitude.
Focal Depth: Focal depth is the vertical distance between the Hypocenter (Focus) and Epicenter.
Isoseismal: Isoseismals are the lines of equal felt seismic intensity, generally measured on the Modified Mercalli scale. Such maps help to identify earthquake epicenters. They also contain important information on ground conditions at particular locations, the underlying geology, radiation pattern of the seismic waves and the response of different types of buildings. They form an important part of the macroseismic approach, i.e. the part of seismology dealing with non-instrumental data. The shape and size of the isoseismal regions can be used to help determine the magnitude, focal depth and focal mechanism of an earthquake.
Foreshock: A small tremor that commonly precedes a larger earthquake or main shock by seconds to weeks and that originates at or near the focus of the larger earthquake. Foreshocks are important for earthquake “prediction”.
Aftershock: An earthquake (adjustments) that follows a large magnitude earthquake called, ‘main shock’ and originates in or around the rupture zone of the main shock. Generally, major earthquakes are followed by a number of aftershocks, which show a decreasing trend in magnitude and frequency with time. Aftershocks are vital for the study of the mechanism of the rupture of the main shock.
Earthquake Swarm: A series of earthquakes without a main shock is called an earthquake swarm.
Aseismic: Unassociated with an earthquake.
Body wave: A seismic wave that travels through the interior of the earth and is not related to a boundary surface.
Elastic wave: A wave that is propagated by some kind of elastic deformation, that is, a deformation that disappears when the forces are removed. A seismic wave is a type of elastic wave.
Liquefaction: The process in which a solid (such as soil) takes on the characteristics of a liquid as a result of an increase in pore pressure and a reduction in stress. In other words, solid ground turns to jelly.
Seismogram: Seismogram is visual record of arrival time and magnitude of shaking associated with seismic wave. Analysis of seismogram allows measurement of size of earthquake.
Subduction: The process in which one lithospheric plate collides with and is forced down under another plate and drawn back into the earth's mantle.
Subduction zone: The zone of convergence of two tectonic plates, one of which is subducted beneath the other.
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