Model Geometries of Extensional Faults: Implication on Structures of the Lower Indus Basin in Pakistan

Abstract

Lower Indus Basin (LIB) in Pakistan is an area of active hydrocarbon exploration related to Mesozoic extension of the Indian plate. Seismic reflection profiles (Ahmed & Ahmad, 1991; Kemal, 1991) show planar, listric normal faults, and horst and graben structures in the lower Indus Basin. Geometry and morphology of normal faults along with physical models of extensional systems are given to provide an insight into the architecture of a passive margin. The model of uniform extension over a non-sloping detachment shows a series of horst and graben structures with planar or listric faults. Uniform extension over a sloping detachments shows dominostyle of faulting. A simple listric detachment produces well developed rollover and a large crestal collapse graben. A listric fault with ramp-flat geometry produces crestal collapse graben and local reverse faults. Model geometries of extensional faults may help to evaluate the structure of the LIB for better hydrocarbon exploration in Pakistan.