Structural Interpretation on the Basis of Focal Mechanism Studies in the Area of Kohat Plateau, Bannu Basin and Western Extension of Salt Range

Abstract

  The identification of structural traps is the main aim in hydrocarbon exploration. A number of techniques are employed for this purpose. Analysis of seismological data through Focal Mechanism Solutions (FMS) is one of these. However this technique has not been widely used in Pakistan for hydrocarbon exploration. Combining published structural information with FMS, it is attempted to identify the surface and subsurface structural pattern. For this purpose, a seismicity map using the earthquake data from international and local seismic networks for the time span 1904-2002 has been prepared. It shows a distinct seismicity pattern in the central Kohat Plateau and along the margins of the Bannu Basin (Khisor, Marwat and Bhittani Ranges). The Bannu Basin itself seems to be aseismic. A total of 9 earthquakes have been investigated, out of which 5 are from Kohat Plateau and the rest are along the margins of the Bannu Basin. Within the Kohat area, 4 out of 5 FMS indicated left lateral strike slip and one shows reverse faulting, which infers wrench faulting in the subsurface. However the margins of Bannu Basin revealed mixed FMS i.e. thrust, reverse and normal. These findings suggest the flower structure (thick-skinned tectonics) geometry due to basement involvement for the study area.