Intraplate stress distribution induced by topography and crustal density heterogeneities beneath the Killari, India, region

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Abstract
The Deccan Traps covered region of the Indian peninsular shield experienced a devastating earthquake of magnitude 6.3(mb&) on September 29, 1993, with the epicenter (18.07°N, 76.45°E) near Killari(Latur). The event had a focal depth of 7 km, and its teleseismic moment tensor analysis suggests reverse faulting characterized by 120°strike, 46°dip, and 100°rake. The fault plane solution of the rnainshock also correlates the reverse faulting with NW‐SE trending nodal plane. In order to gain more insight into understanding the causative factors, the three‐dimensional intraplate lithospheric stresses associated with the topography and subsurface mass hetrogeneities are estimated up to a depth of 15 km beneath a region surrounding the epicenter and lying between 17°–20°N and 75°–78°E. A two‐layered lithospheric model with irregular interface of small amplitude at the Moho has been used for elastostatic stress calculations. The plate boundary force induced stresses are superimposed on the computed stress regime to assess their contribution vis‐a‐vis local causes. The estimated local stresses alone show a subdued northeasterly extensional regime at hypocentral depth. However, the superimposition of an assumed 30 MPa ridge push trending N10°E leads to an enhanced concentration of total stresses beneath the region near the hypocenter. Its maximum value at Killari is 31 MPa at 2 km depth, and it reduces to 29 MPa at 15 km depth. The total deviatoric stresses are also found maximum near Killari. Analysis of computed stresses indicates that the orientation of total principal stresses favors a strike‐slip movement at the focal depth with a NE trending maximum compression. The shear component of these stresses when resolved on the fault plane of the Killari mainshock [U.S. Geological Survey, 1993], however, suggests a thrust movement at 7 km depth beneath the Killari region. This study thus suggests that concentration of total stresses along some kind of crustal weak zones beneath the epicentral region could be an important factor for the reactivation of faults and therefore the Killari earthquake.