The Palghar seismic sequence about 100 km north of Mumbai, Maharashtra, India began on 11 November 2018 with the activity confined between the Western Ghats escarpment and the NW–SE trending west coast fault. Until 31 August 2019, a total of 4854 earthquakes have been located here, whose local magnitude (ML) varied from 0.1 to 4.1. Majority of the earthquakes (~94%) were located in the depth range 4–16km. The precise earthquake relocations reveal two clusters: the N–S trending cluster north of 20.04°N extends to a depth of 10 km, whereas the NE–SW trending cluster to the south of 20.04°N extends to 16 km depth. The shallow northern cluster is noticed to be sandwiched between two mapped mafic intrusions, whereas the deeper southern segment shows earthquakes clustering around the mafic intrusion. The modelled composite focal mechanism solutions for both the north and south clusters suggest normal faulting with a minor strike–slip component as the dominant deformation mode for the Palghar region. From relocated seismicity, we have detected a deeper seismically active zone (with M > 3) at 4–16 km depth, occupying a crustal volume of 1440 km3 (i.e. 20 km (in N–S) x6 km (in E– W) and 12 km (in depth)) that dips toward 20°S and 70°W. This could be attributed to the large crustal stresses induced by the mafic intrusive body below the region.
Figure: Spatial distribution of relocations of 4854 Palghar events and composite focal mechanism solutions for (a) north cluster and (b) south cluster of seismicity.
D. Srinagesh*, Dhiraj Kumar Singh, G. Vikas, B. Naresh, Sunil Roy, Y. V. V. B. S. N. Murthy, P. Solomon Raju, G. Suresh, Prantik Mandal, A. N. S. Sharma, M. Shekar and V. M. Tiwari