Abstract
SUMMARYOn 7 December 2015, a shallow Mw 7.2 strike-slip earthquake struck the Murghab River Valley in the Central Pamirs of Tajikistan. Seismologically this event was similar to a large seismic event in 1911 whose causative fault has never been identified. We measure the displacement field of the 2015 event from satellite observations using Sentinel-1 radar interferometry, Landsat-8 optical pixel-tracking, and surface rupture mapping from high resolution SPOT-6/7 imagery to characterize the role this earthquake rupture plays in the accommodation of strain on its causative structure, the Sarez-Karakul fault. We present geomorphic mapping and interpretations of other Quaternary-active reaches of this fault system, which highlight variable rupture history of the different sections. These sections appear to be separated by inherited bedrock structural boundaries. Significantly, the reaches of the fault northeast and southwest of the 2015 rupture exhibit the freshest morphology prior to 2015, indicative of a more recent rupture than elsewhere. Using new high resolution imagery we map fresh scarps at the northern and southern ends of the Sarez-Karakul fault which may represent this 1911 rupture. To test which of these reaches could have been the source of the elusive 1911 event, we compare synthetic seismograms from three plausible fault sources determined from geomorphology, with observed seismic traces from 1911 at early recording stations throughout Europe. We find that the best fitting fault source is in fact southwest of the 2015 rupture, meaning that we have a record of three distinct recent events on the Sarez-Karakul fault system—two of them instrumentally recorded. Our mapping of these separate events reveals a correlation between their boundaries and the active and inherited thrust and suture systems that intersect the northeast striking left-lateral fault, suggesting structural control over the extents of individual ruptures on the active strike-slip fault.
Highlights
The Mw 7.2 Murghob, Tajikistan earthquake of 7 December 2015, occurred along a high-elevation mountainous reach of the left-lateral Sarez-Karakul fault (SKF), a distinctive northeaststriking structure that cuts across several of the large east-west convergent fault zones and tectonic sutures of the North-Central Pamir mountains (Fig. 1) (Metzger et al 2017; Sangha et al 2017; Gan et al 2018)
We present the first detailed map of surface ruptures from the 2015 Murghob earthquake along the SKF, as well as a near-fault coseismic deformation field from Landsat-8 image pixeltracking that we use in conjunction with interferometric synthetic aperture radar (InSAR) line-of-sight (LOS) displacements to model slip at depth along the ∼80-km-long fault rupture
The 7 December 2015 Mw 7.2 Murghob earthquake occurred along the transtensional Sarez-Karakul fault, separating the northwardconvergent eastern Pamir from the western Pamir, which is deforming under both northward convergence due to the collision of
Summary
The Mw 7.2 Murghob, Tajikistan earthquake of 7 December 2015, occurred along a high-elevation mountainous reach of the left-lateral Sarez-Karakul fault (SKF), a distinctive northeaststriking structure that cuts across several of the large east-west. We present the first detailed map of surface ruptures from the 2015 Murghob earthquake along the SKF, as well as a near-fault coseismic deformation field from Landsat-8 image pixeltracking that we use in conjunction with interferometric synthetic aperture radar (InSAR) line-of-sight (LOS) displacements to model slip at depth along the ∼80-km-long fault rupture. Using these near-field observations, we construct a coseismic slip model with significant detail that allows us to interrogate the role of complexities along the fault which appear to play a role in modulating its slip history. Relating the mapped extents and bounds of these respective ruptures to surrounding tectonic structures, we suggest that the regional geometry of suture zones including contemporary thrust faults and inherited extensional faults, may control the extent of coseismic ruptures along the Sarez-Karakul fault
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