Seismotectonics of the Pamir

Abstract

Based on a 2 year seismic record from a local network, we characterize the deformation of the seismogenic crust of the Pamir in the northwestern part of the India-Asia collision zone. We located more than 6000 upper crustal earthquakes in a regional 3-D velocity model. For 132 of these events, we determined source mechanisms, mostly through full waveform moment tensor inversion of locally and regionally recorded seismograms. We also produced a new and comprehensive neotectonic map of the Pamir, which we relate to the seismic deformation. Along Pamir's northern margin, where GPS measurements show significant shortening, we find thrust and dextral strike-slip faulting along west to northwest trending planes, indicating slip partitioning between northward thrusting and westward extrusion. An active, north-northeast trending, sinistral transtensional fault system dissects the Pamir's interior, connecting the lakes Karakul and Sarez, and extends by distributed faulting into the Hindu Kush of Afghanistan. East of this lineament, the Pamir moves northward en bloc, showing little seismicity and internal deformation. The western Pamir exhibits a higher amount of seismic deformation; sinistral strike-slip faulting on northeast trending or conjugate planes and normal faulting indicate east-west extension and north-south shortening. We explain this deformation pattern by the gravitational collapse of the western Pamir Plateau margin and the lateral extrusion of Pamir rocks into the Tajik-Afghan depression, where it causes thin-skinned shortening of basin sediments above an evaporitic décollement. Superposition of Pamir's bulk northward movement and collapse and westward extrusion of its western flank causes the gradual change of surface velocity orientations from north-northwest to due west observed by GPS geodesy. The distributed shear deformation of the western Pamir and the activation of the Sarez-Karakul fault system may ultimately be caused by the northeastward propagation of India's western transform margin into Asia, thereby linking deformation in the Pamir all the way to the Chaman fault in the south in Afghanistan.

No late Quaternary strike-slip motion along the northern Karakoram fault

“…However, the strong extensional component of the focal mechanisms are opposite what would be expected for a left bend in the dextral Karakoram fault, and we interpret them to be related to westward extensional collapse of the Pamir (i.e. Schurr et al, 2014). end of the Kongur Shan fault system (Fig.…”

“…1C) (Ischuk et al, 2013;Wang et al, 2001;Zhang et al, 2004). Further, recent detailed work on the seismicity of the Pamir suggests the eastern portion of the Pamir are experiencing little internal deformation (Schurr et al, 2014). One complication is the observed seismicity along the dextral Aksu-Murghab fault zone in the southeast Pamir (Strecker et al, 1995), where two earthquakes yielded strongly oblique dextral-normal focal mechanisms (Schurr et al, 2014).…”

“…Further, recent detailed work on the seismicity of the Pamir suggests the eastern portion of the Pamir are experiencing little internal deformation (Schurr et al, 2014). One complication is the observed seismicity along the dextral Aksu-Murghab fault zone in the southeast Pamir (Strecker et al, 1995), where two earthquakes yielded strongly oblique dextral-normal focal mechanisms (Schurr et al, 2014). However, the strong extensional component of the focal mechanisms are opposite what would be expected for a left bend in the dextral Karakoram fault, and we interpret them to be related to westward extensional collapse of the Pamir (i.e.…”

Sedimentology and magnetostratigraphy of the Tierekesazi Cenozoic section in the foreland region of south West Tian Shan in Western China

“…However, such a far-field response should be expressed as more direct and local driving force. Sobel et al (2013) attributed the Oligo-Miocene boundary thermochronological ages observed in the margins of southwest Tarim basin to the initial underthrusting of the Tarim block beneath the surrounding orogens, which has been testified by geophysical data in the sTS, Pamir and West Kunlun (e.g., Matte et al, 1996;Gao et al, 2000;Kao et al, 2001;Li et al, 2001;Buslov et al, 2007;Li et al, 2012;Jiang et al, 2004;Wittlinger et al, 2004;Schurr et al, 2014;Sippl et al, 2013aSippl et al, , 2013bSchneider et al, 2013). The widespread thermochronological records of this episode in West Kunlun and also sTS (Hendrix et al, 1994;Yang et al, 2003;Du and Wang, 2007;Wang and Du, 2009;Chang et al, 2012;Sobel and Dumitru, 1997;Sobel et al, 2006;Chen et al, 2008;De Grave et al, 2012;Macaulay et al, 2014) imply that the onset of underthrusting of the Tarim block during the this episode was not only limited in southwest margin of the Tarim basin, but can also take place in the south and north margins of the basin.…”

Seismotectonic study of the Fergana Region (Southern Kyrgyzstan): distribution and kinematics of local seismicity

“…(2) The Alai region with the Alai Valley (see Figure 1; SW Tien Shan), the Alai range north of the Alai Valley, and the Trans Alai Range south of the Alai Valley, which are all located to the south of the Fergana basin. The Trans Alai is already part of the Pamir mountains (Schurr et al 2014). (3) The Naryn basin, another major intermontane basin within the Tien Shan ranges, is located east of the study area.…”