The 2017 Mw 7.3 Sarpol Zahāb Earthquake, Iran: A compact blind shallow-dipping thrust event in the mountain front fault basement

Abstract

The 12 November 2017 Mw 7.3 Sarpol Zahāb earthquake is one of the largest events to have occurred in the north-western Zagros fold-and-thrust belt during the instrumental period. We use teleseismic and synthetic aperture radar data to study the earthquake source parameters, rupture process and active tectonic characteristics of the event.We find that both data sets individually produce remarkably similar slip distribution, indicative of buried faulting that is consistent with the lack of significant surface rupture.Through the joint inversion of satellite radar and teleseismic data, we find that the rupture propagated rapidly (~3.2 km/s) and asymmetrically along strike to the south, but relatively slowly (~1.5 km/s) in the updip direction, and formed a single large-slip asperity with a peak slip value close to 5 m. Given the regional tectonic context of the distribution of known faults and lithologies, we suggest that the maximum slip is either located in the lowest sedimentary cover or the uppermost basement of the Mountain Front Fault.

Impulsive Source of the 2017 MW=7.3 Ezgeleh, Iran, Earthquake

“…While the rupture directivity imaged here is visible in published slip models (Chen et al, ; Nissen et al, ), the sharpness of the slip pulse in these studies is blurred by their use of far‐field data and smoothing constraints. The good spatial and temporal resolution of our kinematic slip model enabled by the use of near‐field observations reveals interesting features.…”

“…We use a Bayesian framework to infer a population of coseismic slip models that fit available observations. While currently available studies were either limited to the static final distribution of slip on the fault (Barnhart et al, ; He et al, ; Vajedian et al, ; Wanpeng et al, ; Yang et al, ) or used far‐field teleseismic data (Chen et al, ; Nissen et al, ), we jointly invert interferometric synthetic aperture radar (InSAR) and near‐field strong‐motion data which provide a better resolution (Anderson, ) to propose a kinematic description of the earthquake source. We use a layered velocity model that is routinely used to locate earthquakes by the Iranian Seismological Center, which ensures modeling is performed to the best of our knowledge (supporting information Table S1).…”

Seismotectonics of the Zagros (Iran) From Orogen‐Wide, Calibrated Earthquake Relocations

“…In contrast, seismicity in the Lurestan arc is focused strongly along the frontal escarpments and the mapped locations of the Zagros Foredeep and Mountain Front Faults. This includes the recent M w 7.3 Ezgeleh‐Sarpolzahab (2017) sequence, which ruptured an E dipping (∼15°) dextral‐thrust basement fault in the northern Lurestan arc that is approximately colocated with, albeit highly oblique to Berberian's () Mountain Front Fault (e.g., Barnhart et al, ; Chen et al, ; Nissen et al, ). Several of the other mainshock‐aftershock sequences in the Lurestan arc, such as at Moosiyan (2008, 2012), Qasr‐e Shirin (2013), Murmuri (2014), and Mandali (2018), also appear to have ruptured the Zagros Foredeep or Mountain Front Faults (Copley et al, ; Nippress et al, ; Nissen et al, ).…”

The 2018 Mw 7.5 Palu Earthquake: A Supershear Rupture Event Constrained by InSAR and Broadband Regional Seismograms

“…Data weight determination is a tricky and cumbersome process. We followed the procedure described in Melgar et al [30][31][32] and Chen et al [33,34], where the relative weight ratio between ALOS-2 InSAR and broadband regional records was adjusted by trial and error repeatedly until the minimum misfit was obtained ( Figure S3). We employed first derivative temporal regularization on the slip windows and Laplacian regularization on the total slip at each subfault [35].…”