Electrical resistivity imaging of active faults in palaeoseismology: case studies from Karachi Arc, southern Kirthar Fold Belt, Pakistan

ABSTRACT Electric resistivity tomography (ERT) is applied across active concealed faults to confirm the subsurface manifestation and lateral extension of capable faults in Karachi Arc, southern Kirthar Fold Belt, Pakistan. During palaeoseismological investigations, active faults and movements along them are identified using electrical resistivity imaging and trenching. The electrical resistivity images present the general structure of the investigated area, with the possibility of tracking the fault in the subsurface. The verification of faults and comparison of ERT profiles with the excavated trench logs confirmed the success of ERT. The results of ERT and trenching in three major parts of Karachi Arc show: (i) the southern inner part of the arc was inactive in Late Quaternary time, where the Sona Fault did not experience any recent movement; (ii) Kirthar and Khud faults in the northwestern part of the study area are active but do not extend into the southern Karachi Arc; and (iii) the frontal part of Karachi Arc is characterised by Quaternary faulting of limited strike length with a moderate rate of seismic activity. Based on the Karachi Arc case studies, ERT is found to be a reliable geophysical technique for studying near-surface geological structures, subsurface lithological mapping and fault characterisation.