Abstract

With the aim of ground-motion estimation in the region of Jabalpur, India, which suffered serious damage during the 21 May 1997 earthquake (Mw 5.8), we analyze an event that occurred on 16 October 2000. This earthquake was recorded by broadband seismic stations of Jabalpur (jpbl, Δ = 45 km) and Rewa (rewa, Δ = 173 km), and a few other stations at regional distances. Seismic phases constrain the depth of the focus to 27 km. Regional centroid moment tensor inversion of long- period waves at farther stations (Δ > 250 km) yields a focal mechanism with one of the nodal planes characterized by: strike φ = 57°, dip δ = 43°, and rake λ = 22°. A similar focal mechanism is obtained from the inversion of filtered JBPL and rewa data. Compared with the earthquake of 2000, the 1997 event was deeper (36 km) and the corresponding nodal plane (φ = 61°, δ = 64°, and λ = 74°) involved less strike-slip component. The seismic moment obtained from S-wave spectra is 1.36 × 1016 N m (Mw 4.7). Within the framework of the ω2-source model, the high-frequency level of the source spectrum of the 2000 event requires Δσ = 42 MPa. The same Δσ was estimated for the 1997 earthquake, suggesting that the stress drop of subcrustal earthquakes in the Jabalpur region may, in general, be high. We simulate ground motions at JBLP site assuming a ω2-source model and Δσ = 42 MPa and using the random vibration theory (rvt) and the empirical Green’s function technique. The predicted attenuation curves from rvt fit observed peak ground acceleration (pga) and peak ground velocity (pgv) data from the events of 2000 and 1997 (45 < R < 1650 km) within a factor of about 2. These curves predict pga and pgv of 120 cm/sec2 and 4.5 cm/sec, respectively, in the epicentral region during the 1997 Jabalpur earthquake. The corresponding values for the proposed maximum credible earthquake in the Jabalpur area (Mw 6.5, h = 30 km, Δ = 20 km) are 235 cm/sec2 and 13 cm/sec, respectively. The simulated ground motions at JBPL, with Δσ = 42 MPa, along with the transfer functions now available from an extensive microzonation study of the area, may be used to predict ground motions in the Jabalpur area during future earthquakes.

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