Three different types of earthquake sequences in the Deccan Volcanic Province of India

Abstract

• Earthquake foreshock-aftershock sequences are classified into three categories. • The Deccan Volcanic Province hosted all the three categories. • Reservoir filling caused the change from Type-I to Type-II sequences. • Intense rain caused the change from Type-I to Type-III sequences. • Near field study of earthquake source is the key to comprehend the change. Earthquake sequences are broadly classified into 3 categories by Mogi (1963a, b). The Deccan Volcanic Province (DVP) of India witnessed earthquake sequences belonging Type 1 (Latur earthquake of M 6.2 on 29 September 1993), Type 2 (Koyna earthquake of M 6.3 on 10 December 1967), and Type 3 (Palghar earthquake swarm 2018-2020). It has been proposed that the change in the mechanical properties in the shallow crust due to loading of water reservoir has caused the change from Type 1 to Type 2 earthquake sequence for Koyna. Similarly, intense rain is considered to cause the change to Type 3. However, how these changes occur is not well understood. It is hoped that the detailed near field studies of earthquakes being undertaken at Koyna through deep bore-hole observations in the immediate vicinity of the hypocenters of earthquakes will provide an explanation.