A PRELIMINARY ONE DIMENSIONAL CRUSTAL VELOCITY MODEL FOR HIMACHAL PRADESH, INDIA

Abstract:

ABSTRACT: The preliminary 1 D velocity model for Himachal Pradesh, India have been obtained by utilizing the travel-time inversion of p and s waves recorded in the region. For the same we have used the seismic data of 22 three component broadband seismometers having a sampling rate of 100 samples/s that were operated and maintained by Wadia Institute of Himalayan Geology (WIHG), Dehradun in this region from 2004 to 2013. A total of 476 local seismic events having their epicentres within the NW Himalaya with more than six p and s phases were located initially with the HYPO 71 program and the priori velocity model. Out of this 476 seismic events a mere 125 events with maximum least square residual error of 0.40s was used for travel-time inversion. After a number of iterations for the above mentioned dataset we observed that the least square residual misfit is almost constant at 0.03s. This shows that the iteration has reached its final solution and the velocity model obtained is the minimum 1 D velocity model. The resulting relocation shows a maximum seismicity upto a depth of 30 Km which matched with the ongoing tectonic activity in the region. Later the JHD technique is applied taking the station corrections into account for testing the accuracy of the model and we observed that the misfit in hypocentre location has reduced to ±1 km which confirms the accuracy and stability of the proposed 1 D velocity model.