Fault interaction and earthquake triggering in the Koyna-Warna region, India

Earthquakes in the Koyna-Warna region of peninsular India are considered to be reservoir triggered. However, analyses of the available earthquake data indicate that the sustained high seismicity in this region may be influenced also by the geometry of the fault zones and their interactions through stress transfer. These distinct fault zones, inferred from the earthquake distribution and their focal mechanisms, are favourably oriented to each other in such a way that earthquake occurrences in one of the fault zones increase static stress on the other, facilitating frequent and continuing occurrence of earthquakes in the region. Here we show that though the effect of reservoir operations do promote slip on these faults, stress triggering appears to be an important cause for continuing high seismicity as it brings some of the stabilized faults closer to failure in the manner consistent with the inferred sense of motion.