Focal mechanism solutions and nature of plate movements in Pakistan

Abstract

From the seismic point of view, the territory of Pakistan which lies between latitude 23°–37° N and longitude 61°–75° E is one of the most active zones in the world. The importance of this area lies in terms of movements of the Indian plate with respect to Eurasia on the west. Seismicity, as well as focal mechanism- solutions, throws a considerable light on the nature of forces acting in the area. All the available solutions, along with 12 new ones, have been considered for the present study. Their relationship to major faults in the area is discussed. The majority of the solutions in the central and northern parts show strike-slip faulting with a left-lateral sense of motion, followed by thrust faulting; few show normal faulting. This suggests that the Indian plate is moving with respect to the Eurasian plate along the Chaman fault, Quetta transverse zone, Sulaiman Ranges and the Hazara thrusts region joining the Hazara/Kashmir syntaxis. The orientations of P and T axes have been studied. It is seen that in a large number of cases compressive stress is acting nearly in NNW-SSE to N-S directions. The Hazara thrust region appears to be the most complex. Here, the influence of the Himalayan thrust front is evident to a large extent. The nature of faulting along the Chaman fault and Quetta transverse zone is to some extent similar to that of the San Andreas fault system of California. So far as the energy release is concerned, the maximum energy is being released in the form of strike-slip movements close to the Chaman fault and Quetta transverse ranges.