Abstract

Global Positioning System measurements performed over a 2–4 yr period confirm the Xianshuihe-Xiaojiang fault system as one of the primary active structures in southwest China. Stations southwest of these faults show southerly motions of 5–15 mm/yr relative to the western Sichuan basin, and stations in a 200 km geodetic network located northwest of the basin move at only 0–5 mm/yr. These results are consistent with clockwise rotation of southwestern Sichuan and western Yunnan about the eastern Tibetan syntaxis, accommodated by left-lateral slip of 12 ± 4 mm/yr on the Xianshuihe-Xiaojiang fault system. The results imply that if eastward extrusion of crustal material from the plateau occurs at present, it is not accommodated by east-west shortening along the margin of the plateau and must involve wholesale eastward motion of low-lying regions to the east.

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