On 24 September 2019, an M-w 5.9 earthquake struck near the Mangla reservoir in northeastern
Pakistan and resulted in 39 fatalities and 746 serious injuries, making it the deadliest
earthquake in the region since the 2005 M-w 7.6 Kashmir earthquake. Here, we integrate
geodetic, seismic, and field observations to characterize the source properties and
impact of the Mirpur earthquake as well as investigate whether it might be a reservoir-induced
event. From inverting Interferometric Synthetic Aperture Radar data, we find that
a fault with strike similar to 310 degrees, dip similar to 6 degrees, and rake similar
to 117 degrees is the optimal source, with slip concentrated between 5 and 6 km depth.
This is consistent with our relocated aftershocks depth distribution and the lack
of surface rupture observed in the field. Therefore, we infer that the earthquake
ruptured the Main Himalayan Thrust (MHT). The event's shallow depth might explain
the extensive damage caused despite its moderate magnitude, with a maximum shaking
intensity of VIII based on our field survey. The survey also revealed extensive damages
associated with earthquake-induced liquefaction. Our modeling shows that loading due
to increased reservoir water level in the three months before the Mirpur earthquake
led to Coulomb stress increase of similar to 7-10 kPa on the rupture plane. However,
this effect is - 10 times smaller than the Coulomb stress increase due to the 2006
Mangla earthquake, and the Mirpur earthquake only occurred similar to 1-2 weeks after
peak water level. These suggest that pore pressure diffusion contributed to promoting
the fault rupture at a time when it is close to failure due to accumulated stress
from inter-seismic loading. Because the Mirpur earthquake resulted in a stress increase
of >0.2 MPa on the surrounding sections of the MHT and nearby faults, future rupture
of these faults is a significant hazard and proper management of reservoir operations
is necessary to prevent further elevating the seismic risk.
