Seismic Activity along the Main Boundary Thrust (MBT), Pakistan
Abstract
Main Boundary Thrust (MBT) is the main frontal thrust of the Himalayan range, which runs about 1500 km from Assam in the east to Kashmir in the west. The MBT fault zone represents very high earthquake potential in this region, as it is the source of many earthquakes, which are amongst the greatest ever-recorded events. These include 1905 Kangra earthquake of M 8.6, 1934 Bihar-Nepal earthquake of M 8.4 and the great Assam earthquakes of 1897 and 1950. The rupture, which caused these eapthquakes, is occurred in the detachment in the vicinity of the surface trace of MBT.
Keeping the above fact in view, a seismicity map of the area within the 100 km of the MBT have been prepared using the seismological data from various sources for the period of 1904-2004. On the basis of the spatial distribution of the epicenters, the MBT is considered to be active. Focal mechanism studies (FMS) of three events for the period of 1989-1993 within the MBT forming the western portion of Hazara Kashmir Svntaxis (near Islamabad) have been carried out. Two of them are left lateral strike slip, whereas one is thrust with minor left lateral strike slip component. Dominance of strike slip over thrusting/reverse has been observed with the clear indication of the left lateral splays activation of MBT. However, more data is required to confirm this interpretation.
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