Size of Earthquakes

Abstract

Earthquake size is one of most fundamental source parameter to be used in seismic catalogs. A reliable measure of the “size” of an earthquake is essential for seismological, geological, engineering, seismic risk analysis and scientific researh. The size of a seismic source is measured using two parameters; damage caused (intensity) and energy released (magnitude). Intensity describes the strenght of a seismic event in terms of human recognition, affected region, damage on structures. Intensity depends on local geological conditions, distance from the source that make the objective estimates difficult. Intensity scales are valuable not only for pre-instrumental period for historical earthquakes but also for seismic risk analysis. Intensity scale is classified by macroseismic scales. The advent of seismic recording systems made it possible to determine strength of a seismic event from instrumental data. The concept of magnitude was introduced by Richter to provide objective measure of earthquake size. Magnitude of an earthquake provide quick information on the strength of a seismic event for public and are essential for cataloging. Changes in instrumentation and magnitude formulation resulted calculation of different magnitude scales. In order to obtain a non-saturating uniform magnitude scale, seismic moment magnitude (Mw) is developed based on source parameters.