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 teleseismic waveforms is obtained with a simple 4.2-s-long pulse that releases a moment Mo = 1.8 x 10(18) nm from a reverse fault rupture with strike, dip, and rake of 126 degrees, 46 degrees, and 100 degrees, respectively. A approximate to 10-km-wide meizoseismal area is tightly defined by relative casualty count; in the center of this area, aftershock hypocenters (Baumbach et al., 1994) outline a southwest dipping rupture that extends 5.5-8 km along strike and from the surface 8-10 km along 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-km-long zone of compressional scarps which are spatially correlated with the rupture outlined by hypocenter,. In the central portion of this zone, the scarps are multiple and face in opposite directions. Deformation 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 offset 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 shear but were not associated with a zone of preexisting breccia and mineralization. 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 basalt 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 the first impounding of a nearby reservoir was interpreted by some as a possible precursor to a larger earthquake before the 1993 mainshock. Precursory seismicity and artificial effects that cause significant-mechanical changes in the crust may provide an indication of future potentially damaging earthquakes in stable continental areas.