GEOMORPHIC RESPONSE TO AN ACTIVE TRANSPRESSIVE REGIME: A CASE STUDY ALONG THE CHAMAN STRIKE-SLIP FAULT, WESTERN PAKISTAN

The Chaman left lateral strike-slip fault bounds the rigid Indian Plate boundary at the western end of the Himalayan-Tibetan orogen and is marked by contrasting topographic relief. Deformed and faulted landforms along the fault provide an excellent record for understanding this actively evolving intra-continental strike-slip fault. The geomorphic response to this active fault has been studied to evaluate its kinematics utilizing Digital Elevation Model (DEM) data integrated with Advance Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Visible Infra-Red/Short Wave Infra-Red and QuickBird Image data, and geologic/geomorphic mapping along an active strand of the fault in western Pakistan. DEM data from Shuttle Radar Topography Model (SRTM) is compared with the 30 m and 15 m DEM derived from ASTER stereo images. The 15 m ASTER DEM proved to be most useful in delineating topographic changes, whereas ASTER band ratios of 5/7-5/1-5/4 and 4/5-6/7-3/4 and Principal Component Analysis (PCA) were effective in differentiating different rock types and Quaternary landforms/sediments. This study provides the first reconstruction of the geomorphic history of ~400 km² area with the contrasting lithologies of metavolcanics and metasediments for the region. Mapped abandoned stream channels, uplifted and displaced alluvial fan surfaces, stream terraces, and shutter ridges reflect a tectonic-controlled geomorphic evolution as dryland condition in the study area has limited impact on landform preservation and a direct relationship among topography, erosion/uplift and strike-slip deformation can be estimated. Along the strike of the Chaman Fault in this area, dragged and elongated landforms, and shutter ridges support continuous creeping, while surface ruptures, beheaded streams and sharp lithologic contacts are indicative of single event, episodic left-lateral deformation. Shallow concaved and longitudinal stream channels, orthogonal to fault scarps, and gentle slopes with almost no slope failure are indicative of a strike-slip dominant deformation, while the fining upward sequences within the alluvial fans indicate a rapid undercutting and associated high reliefs after each earthquake event. Thus the initiation and cessation of each event is equally reflected by the preserved landscape.