Basement Neo-Tectonics of Western Himalayas from Seismic and Gravity Data Perspective

Abstract

An earthquake of magnitude (Mw) 4.3 occurring on April 6, 2024 near Sargodha (Mianwali NW Punjab, Pakistan) has been analyzed through waveform inversion to understand the subsurface geological structure. This shallow-depth (19 km) event represents a strike-slip faulting with a dextral sense of movement. Gravity data of the epicentral area depicts distinct anomalies representing two separate blocks showing an off-set in the same direction as determined by the seismic inversion validating
modeling results. In our opinion, these structures represent second-order tectonics, potentially emerging as a response to the hindrance caused by the Sargodha High to southward movement of the Himalayan deformation front. Alternatively, R-shears associated with the western boundary of the Indian plate could provide another explanation for such strike-slip mechanism events. Crustal shortening along the deformation front is being accommodated through aseismic slip along a viscous
décollement in the Salt Range and seismic slip within the brittle basement rocks of the Sargodha region as represented by the analyzed seismic event. This dual process plays a key role in shaping the tectonic features in study area. Detailed studies of small to moderate seismic events can help in delineating the subsurface seismogenic structures for development of better seismo-tectonic model for realistic seismic hazard assessment in the region.