Active faulting and seismicity, Northwest Pakistan: a case study of Peshawar Basin Pakistan

Abstract

Active Faults in urban and densely populated areas are of great importance to understand, as these faults may be of high risk to life and property. Peshawar Basin covers Peshawar, the capital of Khyber Pakhtunkhwa, and other populated areas of the Swabi, Mardan, Nowshera, and Charsadda districts. This research article focuses on active faulting and seismic activity in the Peshawar Basin. Fault causes a sudden release of energy in the form of an earthquake when stress exceeds the Strength of a rock. More than 12,000 earthquakes have been reported in the Peshawar Basin, ranging from 1 to 5.7 on the Richter scale. The shallow nature of these earthquakes is a clear indication of ongoing tectonic activity in the region, resulting in active faults in the Peshawar Basin. Intense Field observations and detailed Digital Elevation Model (DEM) analysis analysis confirm active faults in the Peshawar Basin. Field observations of Peshawar Basin cover the study of infrastructures along the active faults where only 10% of the rocks are exposed. Fracture data was collected from infrastructure and this data was carefully analyzed as well. Based on this analysis six active faults are marked. Charsada-Takhbhai Fault, Mardan Fault, Pir Piai Fault, and Swabi Fault are marked as normal, whereas Pir Sabak and Ghorghushti Fault are thrust faults in nature. Normal faults and tilting were also observed in the alluvial deposits, on a small scale, but it is a manifestation of the same phenomenon on a larger scale in the Peshawar Basin. In the Southern part of the Peshawar Basin, active faults were identified and recognized in the near past. This research is significant because it covers the whole Peshawar Basin and this study was never done before. This research shows that these active faults particularly the Swabi fault may be of high risk to the world’s largest earth-filled Tarbela dam and surrounding areas. Subsidence of more than 2 cm per year is observed in the area along the Swabi and Ghoghasti faults.