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Modeling of the 21 May 1997 Jabalpur Earthquake in Central India: Source Parameters and Regional Path Calibration

¹ URS Corporation
566 El Dorado Street
Pasadera, California 91101
chandan_saikia{at}urscorp.com

The primary objective of this study is to model regional and far-regional seismograms recorded from the 21 May 1997 Jabalpur earthquake (M_w 5.8) in central India to calibrate the propagation path in and around the Indian subcontinent. To accomplish this goal, we first established its source parameters ( = 65°, = 68°, and = 70°, h = 35 km) and source complexity, which consisted of two sources with a total seismic moment of 5.88 x 10²⁴ dyne cm and a source 1 to source 2 moment ratio of 1:4 by modeling teleseismic P and depth phases. Source parameters were independently verified by modeling near-regional seismograms of three stations, namely BHPL (Bhopal), BLSP (Bilaspur), and HYB (Hyderabad), by using the same source complexity established in the teleseismic modeling and station-specific wave-propagation path models. The earthquake was relocated by fixing its depth at 35 km and using travel times of teleseismic P, pP, sP phases and regional P and S phases. The International Association of Seismology and Physics of the Earth’s Interior model was used for the location with its crust replaced by the regionalized crustal model. The relocation parameters were: origin time, 22h51m30.80sec ± 0.83 sec; latitude, 23.083° N; longitude, 80.091° E; h = 35 km. With this relocation, source-specific station corrections were established that, in turn, were used to relocate its largest aftershock. Next, we analyzed the composition of regional phases to understand how they were excited, especially how up-going and down-going seismic waves evolved and interfered as a function of distance. This understanding and the newly derived source information were used to calibrate station-specific paths to other far-regional and upper-mantle stations. To this end, we modeled amplitude and travel times of different phases, such as the P_nl, S, SmS, Sm(up)S, and surface waves observed at far-regional stations (5° 25°). This study established far-distance wave-propagation models for paths toward CHTO (Chiang Mai, Thailand), LSA (Lhasa, China), and AAK (Ala-Archa, Kyrgyzstan). We also calibrated a wave-propagation model for a path from northwest India to station NIL (Nilore, Pakistan) using seismograms recorded from an earthquake near Pokhran, the nuclear test site in India.

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