Episodic Uplift along a Quaternary Fault, A Signature of Active Deformation in Frontal Part of Karachi Arc, Southern Pakistan

Abstract

The southern part of Kirthar Fold Belt represents a divergent wrench regime marked by open arcuate
structures, collectively called as Karachi Arc. The frontal part of Karachi Arc is being actively deformed. The
active deformation is manifested by the neotectonic features recorded in the recent sediments. Frontal part of
northern Karachi Arc has been investigated to locate Earthquake Environmental Effects (EEE) in Bizan Dhoro area
northwest of Hyderabad. A linear structure in Bizan Dhoro area at frontal part of northern Karachi Arc has been
investigated. The structure was interpreted in front of Laki Range with the help of LANDSAT ETM and SPOT
Images. The lineament on ground is represented by a NNW oriented linear topographic step in the peneplain
alluvial fans. The frontal peneplain of Laki Range is constituted by the alluvial fans composed of clast supported
gravel ranging from pebble-to-boulder in size laid down by Bizan Dhoro and its tributaries. Four new generations
of alluvial fans have been recognized across the lineament which suggests that the area has experienced at least
three episodes of uplift along the topographic step named as Bizan Dhoro Fault. Electric resistivity tomography
across Bizan Dhoro fault and evidences of tectonic geomorphology revealed that it is a capable reverse fault
dipping at an angle of 60° towards west which has experienced at least three events after deposition of Quaternary
alluvial fans. No brittle deformation however could be recorded in the gravels. Bizan Dhoro fault is an embryonic
structure that depicts active deformation of foreland parallel to the fold and thrust belt.