An Insight into the Characteristics of the September 24, 2019, MW 5.8 Mirpur, Pakistan, Earthquake and Reconnaissance of the Induced-Failure Modes in Buildings and Civil Infrastructure Facilities

A shallow earthquake (M-W=5.8; depth=10 km) hit the Mirpur City of Pakistan at 16:01 local time on September 24, 2019. The earthquake severely damaged RC structures, low-rise brick masonry structures, and various other civil infrastructure facilities. The close location of seismic stations to the damaged area provided the opportunity to assess the seismic response of the buildings subjected to real ground motions. This study aims to provide insight into the failure modes during a field reconnaissance trip following the 2019 Mirpur, Pakistan, earthquake. Damage procedures and causes were determined by analyzing the specific responses of the site to the ground motions and comparing them to the spectral intensity of the ground motions recorded in the vicinity. Insights gained from the damages were then used to identify specific design requirements or general design principles. The findings suggest strong relevance of the vertical component of the Mirpur, Pakistan, earthquake with excessive axial force demands in masonry piers in addition to various inherent structural properties such as soft-story mechanisms. Poor construction practices and nonseismic detailing combined with deficient structural materials induced major seismic damages in brick masonry and reinforced concrete structures. It is concluded that damage from short-period ground motion originating at shallow depths can be exceptionally serious for unreinforced brick masonry (URBM) structures, even with low-magnitude ground accelerations. Dominant failure modes observed in this investigation suggest excessive axial compression or shear-axial compression, shear-flexure cracking, slab rotations, foundation settlement, and soft-story mechanisms. The damage survey highlighting the observed failure modes serves as a useful tool for researchers and practitioners in formulating seismic-resistant design guidelines.