Detailed Active Fault Map of the Spin Ghar Fault System and Related Seismicity in Eastern Afghanistan

Abstract

The Spin Ghar fault system is one of the major active structures in northeastern Afghanistan, stretching ~130 km east-west along the Spin Ghar Mountains in the Jalalabad Basin. The fault system includes a group of strike-slip and oblique-slip thrust fault strands only 25 km from Jalalabad City. However, there is no existing detailed map of the fault traces, which is essential for mitigating seismic hazard from future seismicity. We therefore studied the fault-related geomorphology based on the interpretation of satellite images and shaded-relief topography. To identify exposed lithologies within the area we used true colour and false colour composite (FCC), band rationing and principal component analysis (PCA) on multispectral imagery. The Spin Ghar fault system is marked by both continuous and discontinuous linear and arcuate fault scarps developed in piedmont alluvium and along the Spin Ghar Mountain front. We also recognised scarps cutting bedrock terrain. Several deformed surfaces of Neogene-Quaternary age are observed along the fault strands in the Jalalabad Basin. The basin is also traversed by a series of east-west arcuate folds that suggest the area is undergoing south-north compression. The Quaternary faulting and seismicity demonstrate the kinematics of faulting in eastern Afghanistan. Our observations suggest that the east-west–trending right-lateral strike-slip and oblique-slip thrust faults are active and are important components of the seismic hazard in the eastern Afghanistan.