Seismic source characterization and aftershock relocation of the 2019 Mw 5.8 Mirpur earthquake sequence, Pakistan

Abstract The complex tectonic framework of the 2019 Mirpur seismic sequence was investigated using local seismic data. Moment tensor inversion was performed for the Mirpur mainshock (Mw 5.8) and its largest aftershock (Mw 4.7). The mainshock is characterized by a low dip angle (~10°) and shallow focal depth, suggesting its association with the Main Frontal Thrust (MFT). In contrast, the largest aftershock exhibits a comparatively higher dip angle, indicating deformation along a ramp or ramp-anticline structure. The present-day stress regime was evaluated using moment tensor solutions from two locally inverted events, two Global CMT solutions, and one previously published focal mechanism. The results indicate a maximum horizontal stress (SHmax) orientation of N07°E, consistent with the stress orientation for the 2005 Kashmir earthquake sequence and in agreement with regional compression driven by ongoing Indian plate convergence. After-shock relocation and spatial distribution patterns suggest post-seismic stress relaxation and the possible activation of a higher-dip fault segment or ramp-anticline structure. Although a seismogenic depth of approximately 15 km was estimated, the concentration of seismicity around ~10 km depth may indicate involvement of the Main Himalayan Thrust (MHT). We propose that the Mirpur mainshock was primarily triggered by movement along the MFT, whereas subsequent aftershocks reflect post-seismic relaxation associated with the MHT and related ramp-anticline structures.