Velocity structure and hypocentral location of earthquakes by simultaneous inversion method: Application to the area of Kalabagh,Pakistan

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.