Remote Triggering of Earthquakes in the Koyna-Warna Reservoir Zone, India
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Remotely dynamically triggered earthquakes or tremors observed in many regions around the world are caused by the passing of surface waves of large magnitude earthquakes which have occurred at considerable distances. We present evidence for remote dynamic triggering in the Koyna-Warna region of western India, which is known to be a premier site of reservoir-triggered seismicity (RTS). We conduct a systematic search for dynamic triggering following 20 large distant earthquakes with dynamic stresses of at least 1 kPa in the region. We found dynamic triggering in the region during the Magnitude 8.6 Indian Ocean earthquake of April 11, 2012 and its aftershock of magnitude 8.2. Other competitive large distant earthquakes including the March 11, 2011, Mw 9.1 Tohoku-Oki earthquake and the April 25, 2015, Mw7.8 Gorkha, Nepal earthquake do not trigger the seismicity in the Koyna-Warna regions.  

The increase of microseismicity in the region lasted for up to 5 days, including a magnitude 4.8 earthquake occurring on April 14, 2012. Our results suggest that the Koyna-Warna region is stress sensitive and susceptible for remote dynamic triggering for a stress threshold of ≥20 kPa.

For Further Details:

Bansal, A. R., Purnachandra Rao, N., Peng, Z., Shashidhar, D. & Meng, X. (2018). Remote Triggering in the Koyna-Warna Reservoir-Induced Seismic Zone, Western India. Journal of Geophysical Research: Solid Earth, 123. external link

Figure : Seismic network in the Koyna–Warna region along with the background seismicity since 2005 (gray circles), remotely triggered earthquakes during surface waves of large teleseismic events (red circles), during 24 hour duration (red star) and the seismicity 3 months before the Indian Ocean Earthquake of April 11, 2012 (blue circles). The size of circles in the background seismicity is scaled to its magnitude. The largest earthquake of M6.3 recorded in the region on December 10, 1967 is shown as a purple star. An event of M4.8 occurred three days after the main event of 2012 is shown with its focal mechanism. The triggered events are found north of the Warna reservoir. The inset marks the study region in a larger map of Indian sub-continent and Indian Ocean earthquakes 8.6 and 8.2 are shown as red star. The great circle path for the two Indian Ocean event are also shown as red dotted lines in the inset figure.