Inversions for earthquake focal mechanisms and regional stress in the Kachchh Rift Basin, western India: Tectonic implications

• We have determined the focal mechanism solutions of earthquakes occurring in the Kachchh region.
• P axes of earthquakes in the Kachchh region are oriented horizontally in north–south direction.
• Stress field inversion yields maximum compressional axes trending north–south.
• Principle compressional stress axis plays a key role in controlling seismotectonic processes.

More than a decade after the 2001 MW 7.7 Bhuj earthquake in western India, aftershocks up to MW 5.0 are still continuing around the rupture zone in the Kachchh Rift Basin. Over the years, some surrounding faults in the region have been activated, and a transverse fault generated an MW 5.1 earthquake in 2012. Most of the earthquakes occur in the lower crust at depths between 15 and 35 km. We have determined focal mechanism solutions of 47 earthquakes (MW 3.2–5.1) that were recorded by a 60-station broadband network during 2007–2014 within an area of 50 km radius of the 2001 main shock. South dipping nodal planes in most of the solutions correlate well with the active faults. The earthquakes near the epicenter of the 2001 main shock primarily show reverse-faulting mechanisms. The surrounding earthquakes in the area, however, show predominantly strike-slip mechanisms. The P axes of the earthquakes mostly oriented in north–south, and the T axes in east–west. However, the orientations of the P and T axes exhibit more complexity near the source area of the main shock. Stress field inversion of the solutions yields a dominant north–south compression, which is consistent with the ambient tectonic stress field owing to the northward movement of the Indian Plate with respect to the Eurasian Plate. The geodetic measurements are in reasonable agreement with our results.