Characteristics of earthquake swarm activity observed in the Palghar region of Indian Peninsula from January 2019 to October 2020

The present study emphasizes the seismic characteristics of earthquake swarm activity of the Palghar region that occurred in the hard strata of Deccan traps of the Indian peninsula. This activity is well monitored by National Centre for Seismology (NCS) from December 2018 to October 2020. The related data inferred that initially before the swarm activation there was a barricade to stop the entry of fluids into the permeable zone. Later the fluids are injected into the fault zone at a feasible place may be near the surface at the time of swarm initiation. Further the associated fluids percolated through several channels in many directions forming a multi-dimensional system of cracks and fissures at the level of swarm progression through two distinctive clusters during the time of present study along normal fault orientations. During this process, the heterogeneous material within the subsurface layers might have experienced a decrease in the effective stress due to the increase in the pore pressure which is the resultant of the percolation of fluids within the permeable zone. The outcome of the results shows a comparable strategic increase in the seismicity after the soil saturation during and after the rainfall in the affected zone. Also, the study of the seismicity accompanying fluid injections indicates that the fluid triggering seismicity is demonstrated by the increased slope of the magnitude frequency distribution in the form of spatial b-value which has been found reliable for a catalogue for Palghar swarm activity. The coulomb stress change is also examined to find out the consistency of stress patterns with the earthquake occurrences in the Palghar region which gives the characteristics of swarm sequence. The study emphasized the fundamental and geo-mechanical behavior of fluid migration through multi-directional cracks and fissures as the cause for the evolution and further growth of the Palghar swarm activity.