ELSEVIER Tectonophysics 304 (1999) 241–255 Crustal seismic velocity structure in the epicentral region of the Latur earthquake (September 29, 1993), southern India: inferences from modelling of the aftershock seismograms V.G. Krishna a,L , C.V.R.K. Rao a , H.K. Gupta a , D. Sarkar a , M. Baumbach b a National Geophysical Research Institute, Hyderabad 500007, India b GeoForschungs Zentrum, 14473 Potsdam, Germany Received 14 April 1998; accepted 17 December 1998 Abstract We present 1-D models of crustal P and S wave velocity structure in the epicentral region of the devastating 1993 Latur earthquake in southern India. Travel time and relative amplitude modelling of a seismogram section of well located aftershocks out to 80 km offset, by reflectivity synthetic seismograms, reveal alternating low-velocity layers (LVLs) for P and S waves in the upper crust at depths of 6.5–9.0 km and 12.3–14.5 km with about 7% velocity reduction. A lower crustal LVL at 24–26 km depth is also inferred by modelling. The seismic activity in the Latur region is essentially confined to shallow upper crustal depths of less than 6 km, above the LVLs. The upper crustal velocity models further reveal a relatively low V p = V s ratio of 1.65, while synthetic seismogram models consistent with the upper crustal P wave reflection phases reveal a Q p = Q s ratio certainly less than 1. A high-conductivity zone at a shallow depth of 6–10 km brought out by broad band MT soundings in this region, is found to be coincident with the upper crustal LVLs. These coincident anomalous properties of the upper crust suggest the presence of fluids (probably in a partially- or slightly under-saturated state) below the hypocentral region of the Latur earthquake and its aftershocks.  1999 Elsevier Science B.V. All rights reserved. Keywords: Latur-earthquake-1993; aftershocks; synthetic seismograms; velocity structure; fluids in upper crust 1. Introduction The devastating Latur earthquake ( M w 6.1) of September 29, 1993, is a rare stable continental re- gion (SCR) earthquake in the south Indian shield. It has the highest documented casualty toll for any SCR earthquake (Gupta, 1993; Johnston and Met- zger, 1994). The location and cause of intraplate L Corresponding author. Fax: C91-40-7171564; E-mail: postmast@csngri.ren.nic.in seismicity cannot be understood in terms of plate tec- tonics. Fuchs (1986) presented a case history of the intraplate seismicity of the Hohenzollern graben in southwestern Germany, that is believed to be induced by stress concentration at crustal heterogeneities, particularly in the brittle upper crust. In the Latur region a set of geophysical measurements has been conducted by the National Geophysical Research In- stitute (NGRI), Hyderabad, immediately following the devastating September 29, 1993 earthquake, in order to study the suspected anomalous structure 0040-1951/99/$ – see front matter  1999 Elsevier Science B.V. All rights reserved. PII:S0040-1951(99)00028-1