Probing fault frictional properties during afterslip up- and down-dip of the 2017 Mw 7.3 Iran-Iraq earthquake with space geodesy

Kang Wang

U.C. Berkeley

Date & Time
Building 3, Rambo Auditorium

On November 12th, 2017, an earthquake of Mw 7.3 occurred near the Iran-Iraq border, causing hundreds of deaths in both countries. The earthquake occurred along the Zagros mountain range, a broad and complex zone of continental collision between the Arabian and Eurasian plates. We use Interferometric Synthetic Aperture Radar (InSAR) data collected by the Sentinel-1 mission to study the co- and postseismic deformation of this earthquake. The fault geometry and coseismic slip distribution are exceptionally well determined, thanks to the excellent quality of the InSAR observations. Most of the coseismic moment release is found to be at a depth range between 15 and 21 km, well beneath the boundary between the sedimentary cover and underlying basement.

Data from all four tracks also reveal robust postseismic deformation during ~ 1 year after the mainshock. Aftershocks during the same time period exhibit a similar temporal evolution as the InSAR time series, with most of the aftershocks being located within and around the area of maximum surface deformation. Both kinematic inversions and stress-driven afterslip simulations show that the observed postseismic InSAR LOS displacements are well explained by oblique (thrust + dextral) afterslip, both updip and downdip of the coseismic peak slip area. Assuming that the afterslip evolution is governed by rate-and-state friction, we estimate the value of (𝑎 − 𝑏) ∗ 𝜎 (where a and b are the rate and state friction-law parameters and 𝜎 is the effective normal stress) updip and downdip of the coseismic rupture. We find that the (𝑎 − 𝑏) ∗ 𝜎 updip of the coseismic rupture is significantly higher than downdip, suggesting either different effective normal stress, or heterogeneous fault frictional properties.

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