Comparison of precursory and non-precursory swarm activity in peninsular India

Abstract

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 have been examined in this paper. Earthquake catalogues have been prepared for both type of swarms. It was found that the non-precursory swarms have shallower focal depths, up to 2 km or so, while precursory swarms/foreshocks are associated with greater focal depths. Also, the maximum 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 distinctive criteria for both type of swarms presented in this study could be refined when additional data becomes available. The occurrence of earthquakes according to all the three types of the model of Mogi, namely I, II and III, expresses the complexity in intraplate stress regimes over peninsular India, which is supported by the focal mechanism solutions.