Remote Dynamic Triggering in the Cambay and Narmada rifts of Mainland Gujarat, Northern Western India following the Mw8.6 Indian Ocean Earthquake

Abstract:

Remote triggering of earthquakes is a well-established and rare phenomenon that has gained prominent attention in the recent past. In this study, we conduct a systematic analysis of dynamic triggering in the hitherto less investigated and low seismically active intraplate Cambay and Narmada rifts of Mainland Gujarat, Northern Western India, due to large teleseismic earthquakes. It is noteworthy that the background seismicity in the study area is very low, with no M>4.5 earthquake since 2006 and no M>5.8 one in the recorded history as per the Indian Historical Earthquake catalog. We thoroughly examine the records of teleseismic earthquakes that occurred between 2006 and 2017, with a peak dynamic stress ≥10 kPa. Although other recent events (e.g.., the 2011 M9.1 Tohoku-Oki earthquake) produced a similar peak dynamic stress, the 2012, Mw8.6 Indian Ocean Earthquake (mainshock) and its largest aftershock of Mw8.2 seem to be the only potential triggering candidates. We could detect triggered microearthquakes and ‘Non-Volcanic’ tremors during the Rayleigh, coda, and after passage of the long-period surface waves of the 2012 mainshock. Interestingly, besides a peak dynamic stress of 59 kPa imparted by the 2012 mainshock, some local secondary processes, such as crustal fluid transport and/or local stress transfer among the faults may be responsible for the persistent elevated seismicity in the study area. A triggered earthquake of Mw2.6 occurred near the Narmada rift approximately 5 hours after the 2012 mainshock. Within 150 km of this Mw2.6 event, only 22 Mw>2.5 events occurred since 2006, which corresponds to a likelihood of 0.5% for an Mw>2.5 on any given day, by a random chance. Investigation of remote triggering in a region where earthquakes are not frequent can offer new insights into earthquakes genesis.