[1] Using the measurements of $726 GPS stations around the Tibetan Plateau, we determine the rigid rotation of the entire plateau in a Eurasia-fixed reference frame which can be best described by an Euler vector of (24.38°± 0.42°N, 102.37°± 0.42°E, 0.7096°± 0.0206°/Ma). The rigid rotational component accommodates at least 50% of the northeastward thrust from India and dominates the eastward extrusion of the northern plateau. After removing the rigid rotation to highlight the interior deformation within the plateau, we find that the most remarkable interior deformation of the plateau is a ''glacier-like flow'' zone which starts at somewhere between the middle and western plateau, goes clockwise around the Eastern Himalayan Syntaxis (EHS), and ends at the southeast corner of the plateau with a fan-like front. The deformation feature of the southern plateau, especially the emergence of the flow zone could be attributed to an eastward escape of highly plastic upper crustal material driven by a lower crust viscous channel flow generated by lateral compression and gravitational buoyancy at the later developmental stage of the plateau. The first-order feature of crustal deformation of the northeastern plateau can be well explained by a three-dimensional elastic half-space dislocation model with rates of dislocation segments comparable to the ones from geological observations. In the eastern plateau, although GPS data show no significant convergence between the eastern margin of the plateau and the Sichuan Basin, a small but significant compressional strain rate component of $10.5 ± 2.8 nstrain/yr exists in a relatively narrow region around the eastern margin. In addition, a large part of the eastern plateau, northeast of the EHS, is not undergoing shortening along the northeastward convergence direction of the EHS but is stretching.

[1] We derive a detailed horizontal velocity field for the southeast borderland of the Tibetan Plateau using GPS data collected from the Crustal Motion Observation Network of China between 1998 and 2004. Our results reveal a complex deformation field that indicates that the crust is fragmented into tectonic blocks of various sizes, separated by strike-slip and transtensional faults. Most notably, the regional deformation includes 10-11 mm/yr left slip across the Xianshuihe fault, $7 mm/yr left slip across the Anninghe-Zemuhe-Xiaojiang fault zone, $2 mm/yr right slip across a shear zone trending northwest near the southern segment of the Lancang River fault, and $3 mm/yr left slip across the Lijiang fault. Deformation along the southern segment of the Red River fault appears not significant at present time. The region south and west of the XianshuiheXiaojiang fault system, whose eastward motion is resisted by the stable south China block to the east, turns from eastward to southward motion with respect to south China, resulting in clockwise rotation of its internal subblocks. Active deformation is detected across two previously unknown deformation zones: one is located $150 km northwest of and in parallel with the Longmenshan fault with 4-6 mm/yr right-slip and another is continued south-southwestward from the Xiaojiang fault abutting the Red River fault with $7 mm/yr left slip. While both of these zones are seismically active, the exact locations of faults responsible for such deformation are yet to be mapped by field geology. Comparing our GPS results with predictions of various models proposed for Tibetan Plateau deformation, we find that the relatively small sizes of the inferred microblocks and their rotation pattern lend support to a model with a mechanically weak lower crust experiencing distributed deformation underlying a stronger, highly fragmented upper crust.

China is a country of intense intracontinental seismicity. Most earthquakes in western China occur within the diffuse Indo-Eurasian plate-boundary zone, which extends thousands of kilometers into Asia. Earthquakes in eastern China mainly occur within the North China block, which is part of the Archean Sino-Korean craton that has been thermally rejuvenated since late Mesozoic. Here, we summarize neotectonic and geodetic results of crustal kinematics and explore their implications for geodynamics and seismicity using numerical modeling. Quaternary fault movements and global positioning system (GPS) measurements indicate a strong infl uence of the Indo-Asian collision on crustal motion in continental China. Using a spherical three-dimensional (3-D) fi nite-element model, we show that the effects of the collisional plate-boundary force are largely limited to western China, whereas gravitational spreading of the Tibetan Plateau has a broad impact on crustal deformation in much of Asia. The intense seismicity in the North China block, and the lack of seismicity in the South China block, may be explained primarily by the tectonic boundary conditions that produce high deviatoric stresses within the North China block but allow the South China block to move coherently as a rigid block. Within the North China block, seismicity is concentrated in the circum-Ordos rifts, refl ecting the control of lithospheric heterogeneity. Finally, we calculated the change of Coulomb stresses associated with 49 major (M ≥ 6.5) earthquakes in the North China block since 1303. The results show that ~80% of these events occurred in regions of increasing Coulomb stresses caused by previous events.

The 20 April 2013 Lushan earthquake occurred on the southern section of the Longmen Shan fault system. Using GPS data from 33 continuous stations, we derive a three-dimensional coseismic displacement field of the earthquake and invert for the location, geometry, and slip distribution of the fault rupture. Our study result indicates that the earthquake occurred on a reverse fault striking N28°E and dipping 43°to the NW, with the maximum slip located at 30.292°N, 102.943°E, and 13 km depth. The rupture is dominated by thrust faulting, with a slight but still statistically significant sinistral component. The seismic moment release is 9.5 × 10 18 N · m, equivalent to a Mw6.6 earthquake. Our results suggest that at the southern end of the Longmen Shan fault zone near the triple junction with the Xianshuihe and Anninghe faults, the kinematic deformation field is no longer block-like, but broadly distributed to accommodate the buttressing effect of deformation around the fault triple junction.

No abstract