Abstract

The intraplate Gujarat region located at the trijunction of three failed rifts, Kachchh, Narmada, and Cambay, is one of the most seismically active intraplate regions of the world. Among these three, the Cambay basin has been investigated thoroughly for petroleum. However, the basin has not been studied from a seismotectonic perspective. For the past few years, the northern part of the Cambay basin is becoming active with reasonably frequent earthquake occurrences. In the past 10 yr, 995 earthquakes have been recorded from the region with a maximum magnitude up to 4.2. Most of the earthquakes are in the magnitude range 1–3. Since 2009, four Global Positioning System (GPS) stations have been in operation in the vicinity of the Cambay basin, and a maximum deformation of 1.8±0.1  mm/yr has been estimated. The GPS‐derived strain rates of 0.020.03  microstrain/yr are prevalent in the region. An average strain rate of 0.02  microstrain/yr in the region can generate an earthquake of magnitude 6.4. The focal mechanisms of the earthquakes have been mostly normal with strike‐slip component and corroborated by the geodetic strain tensors. Most of the seismicity is clustered in the basement ridges, striking along pre‐existing Precambrian trends that cross the Cambay basin. Complex geodynamics have developed around the northern part of the Cambay rift because of the various movements along several faults, presence of basement ridges, and subsurface plutonic bodies in a failed rift, which are creating stresses and causing earthquakes in this part of the rift. We postulated that the highly heterogeneous subsurface structure beneath the northern part of the Cambay rift is creating additional stress, which is superimposing on the regional stress field substantially, and this mechanism is plausibly facilitating the localized extensional tectonics in the region where compression is expected.

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