Characterization of Major Fault Systems in the Kachchh Intraplate Region, Gujarat, India, by Focal Mechanism and Source Parameters

Abstract

The focal mechanism and source parameters of 41 local earthquakes (Mw 4.0–5.1) that occurred in the Kachchh rift basin, which is seismically one of India’s most active intraplate regions, are determined to characterize various active fault systems in that region. The tectonics in the rift basin are heterogeneous and complex. In the present study, it was found that one-third of the earthquakes exhibit reverse mechanism and three-fourth are either strike slip or have some components of strike slip. Thus, we conclude that transverse tectonics are currently dominant in the Kachchh rift. These transverse faults are preferably oriented in the northeast–southwest and northwest–southeast directions in the eastern and western parts of the rift, respectively. The movement is sinistral and dextral on faults that are oriented in the northeast–southwest and northwest–southeast directions, respectively. These transverse faults are almost vertical (dip>70°) and mostly blind with no surface expressions. Most of the significant faults that strike east–west dip toward the south and are listric. The stress drop of these 41 earthquakes ranges between 2.3 and 10.39 MPa. It was found that the stress drop of earthquakes may depend on the focal mechanism and is independent of focal depths. The average stress drop is found to be the highest (7.3 MPa) for the earthquakes that show a dominant normal mechanism accompanied by strike slip (5.4 MPa) and reverse (4.7 MPa). The average stress drop of the Kachchh intraplate region is 5.3 MPa, which is consistent with other intraplate regions of the world. A conceptual model of the fault system in the Kachchh region is proposed, based on the results obtained in the present study.

Deep Seismic Reflection Imaging of Mesozoic Kachchh Rift, NW India: Implications for Evolution

“…The extension‐related structure of the Kachchh rift basin might have reactivated as a strike‐slip fault during the inversion process as a result of regional compressive stresses developed due to collision between the Indian and Eurasian plates since Neogene, which is consistent with geological and seismological data (Antolik & Dreger, 2003; Biswas & Khattri, 2002; Patriat & Achache, 1984). The focal mechanisms of the majority of aftershocks indicate strike‐slip/reverse faulting in the region (Kamra et al., 2020; Mandal & Horton, 2007). Similar is the case with other strike‐slip faults identified in the present study.…”

“…It was found that one‐third of the earthquakes exhibit reverse mechanisms and three‐fourths are either strike‐slip or have some components of strike‐slip. Approximately 90% of the earthquakes in the Kachchh region are found to be reverse, strike‐slip, or a combination of both (Kamra et al., 2020). It appears that transpressional tectonics might be dominant in the region.…”

“…All these differences suggest that the KMF is a strike‐slip fault or north dipping high angle reverse fault. It is constrained from focal mechanisms of aftershock data, which identified the KMF as a steeply north‐dipping reverse fault (Bodin & Horton, 2004; Kamra et al., 2020; Mandal & Horton, 2007). A magnetotelluric study (Mohan et al., 2018) identified the KMF as a near‐vertical dip up to 8 km depth and then as a north‐dipping (50°) fault in the deeper crust.…”

INSA National Report on Seismological Research in India: 2019 – 2022

“…Strong motion data from the network operated by ISR have been used in several engineering seismology applications, such as, estimation of source parameters, site characterization, development of ground motion prediction equation and ground motion modeling. The data recorded from the past decade have been used to characterize various sources in the Kachchh rift and other parts of Gujarat (Kamra et al, 2020). It is found from the study that stress drop of earthquakes (M 4.0-5.1) in the Kachchh rift are in the range 2.3-10.4 MPa with an average of 5.3 MPa.…”