Seismic and GPS evidence for the kinematics and the state of stress of active structures in south and south-central Tibetan Plateau

Since the middle Miocene, widely distributed N-S striking rifts or rift-depressions and NE-NW-striking strike-slip faults have developed as major structures in southern and south-central Tibet. Active structures, seismic mechanisms and directions and rates of movement determined from GPS data are different in south and south-central Tibetan Plateau. In southern Tibet, N-S striking normal faults and a few transtensional/transpressional faults are the main structures, but none of the GPS measurements show eastward movement. In south-central Tibet, NE- and NW-striking transpressional/transtensional faults and several large-scale E-W and WNW-striking dextral and sinistral strike-slip faults are the main structures, and are consistent with the movement direction indicated by the GPS data. On the other hand, the pattern of earthquake data from the south-central Tibetan Plateau, and especially from the eastern and western syntaxes, are very complicated. These structures may be produced by N-S contraction which has resulted in the N-S striking linear structures, parallel to the direction of maximum compressive stress, and conjugate NE- and NW-striking transpressional/transtensional faults on the southern side of the Qiangtang Block, and in the eastern and western syntaxes, but the deformation is not continuous from the south to the south-central Tibetan Plateau. Underthrusting of the Indian Plate under the southern Tibetan Plateau after the Middle Miocene may be the main cause of these structural features.