THE 1993 KILLARI EARTHQUAKE IN CENTRAL INDIA - A NEW FAULT IN MESOZOIC BASALT FLOWS

The M(w) = 6.1 1993 Killari earthquake in central India was one of the deadliest earthquakes to occur in a stable continental area. It had a centroid 2.6 km deep and ruptured to the surface. A good fit of teles eismic waveforms is obtained with a simple 4.2-s-long pulse that relea ses a moment Mo = 1.8 x 10(18) nm from a reverse fault rupture with st rike, dip, and rake of 126 degrees, 46 degrees, and 100 degrees, respe ctively. A approximate to 10-km-wide meizoseismal area is tightly defi ned by relative casualty count; in the center of this area, aftershock hypocenters (Baumbach et al., 1994) outline a southwest dipping ruptu re that extends 5.5-8 km along strike and from the surface 8-10 km alo ng dip. These dimensions correspond with an average displacement of 1. 5-0.8 m and a stress drop of 10-4.5 MPa, respectively. We mapped a 1-k m-long zone of compressional scarps which are spatially correlated wit h the rupture outlined by hypocenter,. In the central portion of this zone, the scarps are multiple and face in opposite directions. Deforma tion features indicate north-northeast directed shortening of at least 0.5 m. A leveling profile of an irrigation canal about 3 km northwest of the scarps displays a one-wavelength warp, about 1 km long and 1.3 m in peak-to-peak amplitude, that may reflect deformation associated with the rupture. Two trenches across the scarps exposed faults that o ffset the soil-rock interface as much as 50 cm. We found no convincing evidence suggesting that these faults existed prior to the earthquake . In the basalt, these faults reactivated exfoliation fractures in she ar but were not associated with a zone of preexisting breccia and mine ralization. The hypothesis that the 1993 rupture is a new fault in the Deccan Traps is consistent with lack of geomorphic evidence of prior faulting and with the lack of accumulated deformation or tilting in ba salt layers exposed as close as few tens of meters from the scarp. No convincing clues about a seismogenic fault have yet been detected from either historic seismicity or geology in the 1993 source area, but a burst of seismicity 1 year before the mainshock and 2.5 years after th e first impounding of a nearby reservoir was interpreted by some as a possible precursor to a larger earthquake before the 1993 mainshock. P recursory seismicity and artificial effects that cause significant-mec hanical changes in the crust may provide an indication of future poten tially damaging earthquakes in stable continental areas.