Present-day distribution of deformation around the southern Tibetan Plateau revealed by geodetic and seismic observations

摘要

The modern kinematics in and around the Tibetan Plateau have been widely investigated; however, the deformation distribution pattern describing the crustal kinematics in this region is controversial. Here, we quantify the deformation distribution in the southern Tibetan Plateau by adopting the partitioning ratio of internal to boundary potency rates instead of the individual slip rate data on major faults used in previous studies. The study area was divided into several blocks by major faults based on geological surveys, seismic data and a significance statistical analysis. For each block, the partitioning ratio of the potency rates was calculated by a microplate model using 294 GPS velocities from 13 studies. The deformation distribution derived from the GPS velocities was validated by surface-wave data from 407 earthquake events. After excluding the potency rates from the boundary between the Tibetan Plateau and Indian Plate, the ratio of intrablock potency rates within the southern Tibetan Plateau was 51%. This suggests that the Tibetan deformation is diffusely distributed over a large range. A seismic data analysis indicated that 53% of the historical seismic moments were released in the modeled blocks since 1901, which supported the conclusion based on the GPS velocities. The F-test indicated that the internal strain in most Tibetan blocks cannot be neglected to fit the surface velocities. Thus, the present day crust in southern Tibet is probably far from a pure rigid block. This is supported by the relatively slow strike slip rates of two major faults: the Karakorum fault (5.9 +/- 0.8 mm yr(-1)) and Karakorum-Jiali fault (4.4 +/- 0.8 mm yr(-1) in the east segment, 9.3 +/- 0.8 mm yr(-1) in the west segment). The large-scale diffuse deformation in the southern Tibetan Plateau reproduced by the microplate model with significant internal strain, with seismic imaging or structural analyses, could further clarify the geodynamic processes in the India-Asia collision zone.