Probing the active kinematics in northwestern Himalayan foreland, Pakistan: Insights from seismicity and gravity data

Abstract

Active tectonic forces and elements along northwestern Himalayan foreland have been probed through determination of seismic parameters duly substantiated by gravity data analysis. Local broadband waveform data of seven moderate to small size earthquakes recorded by CES and PMD networks was analyzed for resolving focal mechanisms and stress orientation. These predominantly strike-slip seismic events represent NW-SE oriented causative faults while the maximum horizontal stress (SHmax) is oriented in the NNW–SSE direction that mimics the Indo-Eurasian plate convergence. Depicted structure was corroborated through analysis of TOPEX satellite gravity data. Shallow right-lateral strike-slip faults observed in gravity data are consistent with the determined focal mechanism solutions. The residual and regional gravity data validates variation in faulting styles with depth as observed in seismic studies. The predominant shallow strike-slip faulting may be associated with interaction of Himalayan thrust and fold-belt with the Indian flexural forebulge known as Sargodha-Delhi basement ridge. Considering these faults to be R-shears of the western plate boundary, i.e. Chaman fault system may provide an alternate tectonic explanation. Total slip in the area, seems to be occurring partly aseismically along viscous decollement in the Himalayan Front i.e. Salt Range and partly seismically through brittle deformation of the basement ridge.