Dynamically triggered events in mining- and monsoon-induced regions of Northwestern Deccan volcanic province of India

Large and shallow earthquakes can trigger seismicity from long-distance ranges, ideally along significant plate boundaries and in active geothermal/volcanic regions. The present study aims to garner evidence for dynamically triggered events in the intraplate Surendranagar and Talala regions of Saurashtra Horst, Northwestern India, which are the premier sites of mining- and monsoon-induced activities, respectively. A routine catalogue analysis did not reveal any apparent dynamic triggering of earthquakes in the Saurashtra region. To investigate the possibility of triggered earthquake signatures in the waveform data, we applied the Matched Filter Technique (MFT) to the waveform data of 31 teleseismic earthquakes with Peak dynamic stresses ≥ 1 kPa, that occurred between 2007 and 2017. Results reveal that one (2017 Mw7.9 Papua New Guinea) event triggered seismicity in Surendranagar and four (2007 Mw7.9 Sumatra; 2009 Mw7.6 Sumatra; 2010 Mw8.8 Chile, and 2012 Mw7.6 Costa Rica) in the Talala region. β-statistics further confirm the triggering. Application of the MFT revealed 81 hitherto unrecognized local events in a 20-hour duration around the triggering mainshocks. Only ∼ 16% of the examined remote mainshocks produced dynamic triggering in the Saurashtra region. The other recent earthquakes, i.e., the 2011 Mw9.1 Tohoku-Oki and the 2012 Mw8.6 Indian Ocean earthquakes, did not trigger any seismicity despite having a significant value of peak dynamic stress. This suggests that the amplitude of surface waves is not a necessary condition for dynamic triggering. A detailed investigation revealed an intriguing observation that the identified seismicity in the study region is more likely to be triggered after the Indian monsoon when the faults are critically stressed. Given the crustal fluids in the region, their presence and/or sub-critical crack growth model may be plausible mechanisms for triggering. The study suggests that mining- and monsoon-related activities may perturb the subsurface stress conditions, making the region more susceptible to dynamic triggering.