Contemporary Crustal Deformation Within the Pamir Plateau Constrained by Geodetic Observations and Focal Mechanism Solutions

Author:	Pan, Z.Y., He, J.K., Li, J.
Abstract:	We used an updated data set of 192 GPS-derived surface velocities and 393 earthquake focal mechanisms (Mw > 3.0, hypocenter depths < 30 km) to evaluate the spatial variations in the surface strain rate and crustal stress regime throughout the Pamir Plateau and its surrounding regions. The strain rate field was estimated using the spline in tension approach that solves for the surface velocity in a rectangular grid and the stress field was predicted from focal mechanism solutions using the damped regionalscale stress inversion (DRSSI) method of Hardebeck and Michael (Journal of Geophysical Research, https://doi. org/10.1029/ 2005jb004144, 2006). The results show that the crustal stress field around the Pamir Plateau is predominantly characterized by NNW-SSE compression and E-W extension, which is consistent with the principal orientations of the two-dimensional surface strain rate tensor. This agreement supports the notion that the Pamir and southwestern Tien Shan are uniformly strained blocks. In particular, the fan-shaped rotational pattern between Shmax and the strain rate from the western Pamir to the Tajik Basin shows that the counterclockwise rotation of the Shmax orientation is associated with vertical deformation, which is consistent with the idea of Schurr et al. (Tectonics 33(8): 2014TC003576, 2014) concerning the gravitational collapse and westward extrusion of the crust in the western Pamir. We propose that such a stress-strain pattern, dominated by NNW-ESE oriented compression and E-W trending extension, originated from a combination of the northward push of the Indian continent and the southward subduction of the Tien Shan.
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Page number:	3463-3484
Issue:	10
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PubYear:	2018
Volume:	175
Publication name:	Pure and Applied Geophysics
Abstract:	We used an updated data set of 192 GPS-derived surface velocities and 393 earthquake focal mechanisms (Mw > 3.0, hypocenter depths < 30 km) to evaluate the spatial variations in the surface strain rate and crustal stress regime throughout the Pamir Plateau and its surrounding regions. The strain rate field was estimated using the spline in tension approach that solves for the surface velocity in a rectangular grid and the stress field was predicted from focal mechanism solutions using the damped regionalscale stress inversion (DRSSI) method of Hardebeck and Michael (Journal of Geophysical Research, https://doi. org/10.1029/ 2005jb004144, 2006). The results show that the crustal stress field around the Pamir Plateau is predominantly characterized by NNW-SSE compression and E-W extension, which is consistent with the principal orientations of the two-dimensional surface strain rate tensor. This agreement supports the notion that the Pamir and southwestern Tien Shan are uniformly strained blocks. In particular, the fan-shaped rotational pattern between Shmax and the strain rate from the western Pamir to the Tajik Basin shows that the counterclockwise rotation of the Shmax orientation is associated with vertical deformation, which is consistent with the idea of Schurr et al. (Tectonics 33(8): 2014TC003576, 2014) concerning the gravitational collapse and westward extrusion of the crust in the western Pamir. We propose that such a stress-strain pattern, dominated by NNW-ESE oriented compression and E-W trending extension, originated from a combination of the northward push of the Indian continent and the southward subduction of the Tien Shan.
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