answer:“Aftershocks differ from other earthquakes only in that we expect them. Unlike most earthquakes, aftershocks occur within predictable bounds of space, time, and magnitude. They are most common immediately after the mainshock and decay in time with approximately the reciprocal of time since the mainshock [Omori’s law, (Utsu, 1961)]. The magnitudes follow a Gutenberg-Richter relation, with the number of aftershocks proportional to ten to the power of the magnitude times a negative constant b. b is close to one so each unit decrease in magnitude leads to an order of magnitude decrease in number [Gutenberg and Richter, 1954]. This leads to a distribution of the largest aftershock that peaks at approximately one unit of magnitude below the mainshock (sometimes referred to as Bath’s law [Richter, 1958]). The above properties of aftershock sequences allow for time-dependent prediction of aftershock probabilities [Reasenberg and Jones, 1989]. ” Source