Estimation of Source Parameters of Local Earthquakes Based on Inversion of Waveform Data

Generalized inversion has been used to estimate the various source parameters using S-wave spectra of 17 local crustal earthquakes recorded at the Dhanbad broadband seismic station, Jharkhand, India. Source parameters of another nine local events were compiled from an earlier study for detailed analysis. It was found from the source parameters of 26 events, that the corner frequency lies between 4.56 and 8.62 Hz, seismic moment between 6.2E + 12 and 2.11E + 16 N-m, stress drop between 0.11 and 37.13 MPa, source radius between 144 and 291 m, source displacement between 0.24 and 229 cm, moment magnitude between 2.44 and 4.82, and seismic energy between 8.3E + 06 and 1.13E + 13 Joule. Various empirical relationships were established based on the results of these 26 events, and it was found that the stress drop, corner frequency, source radius and source displacement are inter-related. Analysis also showed that the source parameters were correlated for stress-drop intervals of Δσ > 3.0 MPa and Δσ < 3.0 MPa, and were interpreted to be caused by interrupted rupture propagation because of strain weakening of the rock masses. The mere correlation between focal depth and stress drop found in the present study apparently accounts for high heterogeneities present in the crust beneath the study area.