Three-dimensional modeling of intraplate stresses in the epicentral zone of the 21 May 1997 Jabalpur earthquake of Mw 5.8, central India

Abstract

Three-dimensional intraplate stresses induced by topography and crustal density heterogeneities have been modeled for a region in central India (latitude: 21–26°N, longitude: 77–82°E) that was affected by the 1927 Son-valley ( M w 6.4) and the 1997 Jabalpur ( M w 5.8) earthquakes. The modeled stresses show that these two events occurred in the zones of significant increase in gradients of the principal stress difference ( σ 1 − σ 3) contours. The highest value of these differential stresses (∼ 90 MPa) is obtained at 5 km depth beneath the epicentral zone of 1927 Son-valley earthquake, whereas, a value of 35 MPa is obtained at the focal depth (∼ 35 km) of the 1997 Jabalpur mainshock. Further, depth sections of estimated differential stresses delineate a south-dipping high stress body penetrating the whole crust (probably a mafic intrusive intruded during the Deccan volcanism episode) beneath a zone (bounded by Narmada north fault in the north and Narmada south fault in the south) within which all aftershocks including mainshocks of the 1997 Jabalpur and the 1927 Son-valley have occurred. The modeled direction of principal stresses, as well as inferred mode of faulting (at 5, 20, 35, and 40 km depths), correlates strongly with the long period (20–50 s) centroid moment tensor solutions for the broadband recordings of the M w 5.8 Jabalpur mainshock. Results suggest that estimated large intraplate stresses associated with an inferred mafic intrusive in the presence of high pore pressure (resulted from the dehydration of the serpentinite minerals) and deep brittle/ductile transition may contribute to the failure of rock along the pre-existing weak Narmada south fault leading to the earthquakes in the deep crust. It is proposed that the causal association of large intraplate stresses and the pre-existing deep crustal faults would control the future locales of earthquakes in the Narmada–Son lineament.