COMPARISON OF PRECURSORY AND NON-PRECURSORY SWARM ACTIVITY IN PENINSULAR INDIA

Earthquake swarms in peninsular India can be classified into two types namely: (1) precursory type which are followed by a larger earthquake ; and (2) non-precursory type implying sudden increase of felt tremors which die off after some time. The characteristics of these tremors h ave been examined in this paper. Earthquake catalogues have been prepa red for both type of swarms. It was found that the non-precursory swar ms have shallower focal depths, up to 2 km or so, while precursory swa rms/foreshocks are associated with greater focal depths. Also, the max imum magnitude of non-precursory swarms has rarely exceeded 4.0 which is lower than that observed in precursory swarms. The time t (in days) from the earliest felt earthquake to the main earthquake of magnitude M is related by M = 1.88 + 1.50log t. This relationship and the disti nctive criteria for both type of swarms presented in this study could be refined when additional data becomes available. The occurrence of e arthquakes according to all the three types of the model of Mogi, name ly I, II and III, expresses the complexity in intraplate stress regime s over peninsular India, which is supported by the focal mechanism sol utions.