The 2015 M_w7.2 Sarez Strike‐Slip Earthquake in the Pamir Interior: Response to the Underthrusting of India's Western Promontory

Abstract

The Pamir orogen, Central Asia, is the result of the ongoing northward advance of the Indian continent causing shortening inside Asia. Geodetic and seismic data place the most intense deformation along the northern rim of the Pamir, but the recent 7 December 2015, Mw7.2 Sarez earthquake occurred in the Pamir's interior. We present a distributed slip model of this earthquake using coseismic geodetic data and postseismic field observations. The earthquake ruptured an ∼80 km long, subvertical, sinistral fault consisting of three right‐stepping segments from the surface to ∼30 km depth with a maximum slip of three meters in the upper 10 km of the crust. The coseismic slip model agrees well with en échelon secondary surface breaks that are partly influenced by liquefaction‐induced mass movements. These structures reveal up to 2 m of sinistral offset along the northern, low‐offset segment of modeled rupture. The 2015 event initiated close to the presumed epicenter of the 1911 Mw∼7.3 Lake Sarez earthquake, which had a similar strike‐slip mechanism. These earthquakes highlight the importance of NE trending sinistral faults in the active tectonics of the Pamir. Strike‐slip deformation accommodates shear between the rapidly northward moving eastern Pamir and the Tajik basin in the west and is part of the westward (lateral) extrusion of thickened Pamir plateau crust into the Tajik basin. The Sarez‐Karakul fault system and the two large Sarez earthquakes likely are crustal expressions of the underthrusting of the northwestern leading edge of the Indian mantle lithosphere beneath the Pamir.

Seismotectonics of the Tajik Basin and Surrounding Mountain Ranges

“…Our seismotectonic analysis is primarily based on the recordings of the TIPTIMON seismic network (Schurr et al, , ), deployed in the Tajik basin, Hindu Kush, and western Pamir between 2012 and 2014. It continues our recent seismotectonic studies of the Pamir that were based on the earlier (2008–2010) deployed TIPAGE seismic experiment (Schurr et al, ; Sippl et al, ) and geodetic data (Metzger et al, ). Thus, our study combines two large temporal seismic networks, together covering the Tajik basin, Pamir, Tian Shan, and Hindu Kush collision system, placing a high‐resolution seismotectonic analysis into a regional tectonic context.…”

“…Transpressive strike‐slip faults, like the Albruz‐Marmul and the dextral Andarab and Herat, accommodate westward lateral motion of crustal blocks from the Karakorum and Hindu Kush (Figure a; Tapponnier et al, ; Treloar & Izatt, ). These fault zones are bounded in the east by a broad, distributed belt of segmented sinistral strike‐slip faults, connecting the Chaman fault of Pakistan and Afghanistan NNE‐ward with the Sarez‐Karakul fault system in the Central and North Pamir (Figure a; Strecker et al, ; Schurr et al, ; Metzger et al, ). Along the Pamir‐Hindu Kush transition, these are the sinistral Lake‐Shiwa and Kapisa‐Nuristan fault systems (Figure a).…”

“…In contrast, the Tajik basin's lithosphere between these mountain ranges was proposed to behave as a relatively rigid block (van Hinsbergen et al, ). Intense crustal seismicity (Burtman & Molnar, ; Fan et al, ; Hamburger et al, ; Lukk & Yunga, ; Nersesov & Popandopulo, ), including seven shallow magnitude 7+ earthquakes within the last century, demonstrates the high seismic propensity within the basin and along its margins (Kulikova, , and references therein; Metzger et al, ). This poses the question to what extent the crustal seismicity is driven by subcrustal processes.…”

The Alichur Dome, South Pamir, Western India–Asia Collisional Zone: Detailing the Neogene Shakhdara–Alichur Syn‐collisional Gneiss‐Dome Complex and Connection to Lithospheric Processes

“…• Table S1-S9 from geodesy, seismology, and neotectonic mapping (e.g., Ischuk et al, 2013;Jay et al, 2017;Kufner et al, 2018;Metzger et al, 2017;Schurr et al, 2014;Sippl et al, 2014;Zubovich et al, 2010). Currently, the Pamir east of the NNE-trending Sarez-Karakul fault system (SKFS; Figure 1) moves northward en bloc, with little internal deformation.…”

Cumulative and Coseismic (During the 2016 Mw6.6 Aketao Earthquake) Deformation of the Dextral‐Slip Muji Fault, Northeastern Pamir Orogen

“…Deformation of the Pamir is not only complicated but is also strongly active, as manifested by fast Quaternary faulting rates and GPS-based modern deformation rates (e.g., Arrowsmith & Strecker, 1999;Chevalier et al, 2011;Fan et al, 1994;Ischuk et al, 2013;Li et al, 2012;Thompson Jobe et al, 2017;Zubovich et al, 2010). Accordingly, the Pamir is characterized by intense seismicity, for example, the 1974 M w 7.1 Markansu event (e.g., Jackson et al, 1979) along its northern margin, the 1895 M 7 Tashkorgan event (e.g., Li, 2013) in its eastern region, and the 2015 M w 7.2 Murghab event (e.g., Metzger et al, 2017;Sangha et al, 2017) in its central region ( Figure 1b). To date, however, the seismic behavior and potential seismic risk associated with major active faults have not yet been well investigated.…”