Velocity structure and hypocentral location of earthquakes by simultaneous inversion method: Application to the area of Kalabagh, Pakistan
Keywords:
Simultaneous inversion; Velocity structure; Local earthquake data; Hypocentral location; Kalabagh area.Abstract
A layered P-wave velocity model in the crust and just below the Moho is estimated for the Kalabagh area. The arrival-time data of p-waves from local earthquakes that occurred within the Kalabagh seismic network operated from March 1981 to September 1990 are used for inversion. A damped least-squares method is applied in the inversion process for determining the hypocenter and velocity parameters simultaneously. The estimated P-wave velocities are 5.33±0.04 and 5.56±0.05 km/s in the upper crust (above a depth of 11km), 6.27±0.03 and 6.57±0.08 km/s in the intermediate crust (from 11 to 25 km of depth) and 6.94±0.09 km/s in the lower crust i.e. up to the Moho discontinuity which is, in this case, at 35.5 km depth. The velocity just below the Moho is found to be 8.00±0.09 km/s. The 90% of relocated events show an epicentral accuracy of the order of 2km or better. Most of the relocated events are found at a depth range of 5 to 20 km, indicating that the active zone lies in this depth range.
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