Seismicity depth distribution analysis in southern Pakistan

Abstract

This study is focused on analytical analysis of spatial dispersion of seismicity depth in southern Pakistan. The southern Pakistan spreads over Sindh, Balochistan, and frontal offshore areas of the Arabian Sea. Thereby, earthquake-prone sources are diversified in their seismotectonic characteristics such as active Makran subduction zone, transform boundary along Murray ridge and Chaman-Ornch-Nal fault system. The drifting mosaic of lithospheric platform is adding elastic fuel at a rate of 1.5–4 mm/year to the potential faults at shallow, intermediate, and deep levels. Unlike conventional approach, we have fragmented the composite catalog of earthquakes (during 325 BC to 25 February 2020) into different depth slices to reckon comparative seismicity changes at various depth intervals. Seismicity depth patterns are found significant to delineate potential seismotectonic plate boundaries and associated fault network in their intraplate regions. The changes in seismicity characteristics are comprehended with b-value variations for segregated depth windows. The interplate seismicity is observed in various clusters of shallow to deep focal depths, reflecting the seismically active zones of respective plate margins. Critical analysis of focal depths unveiled some anomalous deep focal depths for several intraplate earthquakes located in southern Sindh region. It is suggested to re-estimate focal depth anomalies by identifying uncertainties in data recording procedures or investigate physical mechanisms which synchronized with seismotectonic environments of the region.