Widespread Aseismic Slip Along the Makran Megathrust Triggered by the 2013 Mw 7.7 Balochistan Earthquake

InSAR time series data for the 2014–2021 period reveal up to 20 cm of radar line-of-sight displacements in the area of the 2013 Mw 7.7 Balochistan earthquake northwest of the Hoshab Fault in the eastern Makran subduction zone in southwest Pakistan. We show that surface displacements were caused by ∼80 cm of aseismic slip along a 5,500-km²-wide subhorizontal patch of the megathrust fault. The corresponding moment is Mw 7.3. The percentage of slip in plate-perpendicular direction ranges from ∼65% in the northwest to 96% in the southeast. Slip is consistent with shear stress imparted by the 2013 earthquake. The triggered aseismic slip suggests that this section of the megathrust is decoupled. The implication for the seismic potential of the subduction zone is that the megathrust is fully locked to at most 220 km distance from the trench, consistent with the lack of M ≥ 9 earthquakes in the historic record.