On the Size of an Aftershock Zone of a Large Earthquake

Aftershocks following a large earthquake are an inevitable part of the preparation and occurrence of large earthquakes. Depending on the location of the epicenter, tectonic–structural conditions of the epicentral zone, and earthquake intensity on the Earth’s surface, an aftershock cluster can cover different surface areas. Establishing the quantitative relationships between the aftershock zone and the main parameters of the earthquake (magnitude, rupture length, and slip value) can contribute to improving the model of an earthquake as a natural physical phenomenon. The extents of aftershock and deformation zones, as well as macroseismic changes on the Earth’s surface, indirectly indicate the intensity of the mainshock and the presence of portions with different degrees of weakening of rocks in the epicentral zone. This paper proposes a method to determine the area of such an aftershock zone using a deformational model of earthquake preparation and nucleation proposed earlier by the author. A new expression is obtained for determining the area of an aftershock zone depending on (i) the length of the rupture formed during the earthquake and (ii) the average slip along the rupture; expressions for the logarithmic and linear dependences of this area on the earthquake magnitude are also obtained. It is shown that the areas of the aftershock and deformation zones around an earthquake source are identical.