an earthquake is never an isolated event. a larger shock is likely to be preceded by a few smaller shocks, which are called foreshocks. There are almost certain to be many shocks after a main shock; these are called aftershocks. The aftershocks gradually decrease in frequency and magnitude. The foreshocks and aftershocks are expected to occur in the same epicentre ares of the main shock, and are generally associated with the same fault system of the main shock. On the other hand, a long series of small shocks with no main event may be frequently recorded in certain localities; these sequences are called earthquake swarms. Shallow crustal heterogeneities and rainfall may cause such swarms, even in an less active intraplate region (see Kayal 2008). Sometimes a large earthquake may be preceded by a swarm in a tectonically active interplate region; this type of swarm is called a precursory swarm