The role of crystallized magma and crustal fluids in intraplate seismic activity in Talala region (Saurashtra), Western India: An insight from local earthquake tomography

- High Vp and High Vp/Vs body, possibly crystallized magma, in the upper crust.
- Role of crystallized magma in generation of intraplate moderate earthquakes
- Crustal fluids released from crystallized magma causing swarm activity.

The Talala region in Saurashtra, Western India is one of the seismically active intraplate regions on the Earth. In recent past, this region has been site of moderate magnitude earthquakes as well as swarm-type earthquake activities. To understand the processes of earthquake generation in this intraplate setting, we constrained the earthquake distribution pattern along with the crustal seismic P-wave velocity (Vp) and Vp/Vs variations, using local earthquakes data. We inverted 2470 P- and 2230 S-wave arrival times from 550 earthquakes which were recorded over 11 seismic stations during 2007 to 2012. The earthquakes distribution shows that the seismicity is following ~ NNE-SSW trend, extending for a distance of ~ 25 km and up to 15 km in depth. The seismic tomographic images show that the swarm-type earthquake activities at shallower depths are mostly in the zone of lower Vp and lower Vp/Vs. Whereas, the moderate magnitude earthquakes are occurring in a ~ NW trending zone of higher Vp and higher Vp/Vs, possibly indicating a zone of crystallized mafic magma, which was transported from deeper Earth. This zone represents a pronounced heterogeneity and provides locale for stress accumulation in this region. After 2001 Bhuj earthquake (Mw 7.7), due to stress perturbation the ~ NNE-SSW trending fault got activated and caused bigger earthquakes in this region. Moreover, the crystallized mafic magma is possibly feeding fluids at shallower depths for causing the swarm-type earthquake activities in this region.