Strain modeling in the "Golden Triangle" region using GPS and active faults: interactions with the Eastern Himalayan Syntaxis

Anne Socquet (ENS Paris), Corné Kreemer,,Nicolas Chamot-Rooke (ENS Paris),Claude Rangin (CDF, Aix en Provence), Christophe Vigny (ENS Paris), and Manuel Pubellier (ENS Paris)

Myanmar constitutes the boundary between India and Sunda plates. The deformation is controlled by partitioning between strike-slip motion along the Sagaing fault and wrenching along the Indo-Burma arc. Further to the north, Myanmar active structures connect to the eastern Himalayan Syntaxis, where rotational deformation is accommodated by curved strike-slip faults. Although several GPS studies now constrain the intra-continental deformation field in China, the interaction between crustal flow around the Eastern Himalayan syntaxis and far-field deformation in the "Golden Triangle" remains ill-understood. Here, we combine available GPS surveys with our own geodetic results obtained recently across the India-Sunda plate boundary zone. Haines and Holt (1993) method is used to derive a consistent horizontal crustal velocity field for the entire area. This methodology also allows the inclusion of faults by introducing zones of weakness. Faults rate and style of deformation can be varied and we test different scenarios and their consistency with GPS observations.

The modeled vectors relative to India slightly swing around the Eastern Himalayan Syntaxis, indicating that dextral shear is the dominating process. The swing effect seems to be restricted west of the Xianshuihe Fault, which acts as the western boundary of the South China block. The relative motion between South China and Sundaland is small and the Red River Fault does not seem to localize the deformation, at least in its SE termination. With respect to stable Sundaland, the crust of Yunnan and of the northern part of Sundaland is moving S to SW. This extra volume of crustal material may be accommodated by the building of topography, as suggested by topographic contours, or by lateral motion towards free space, i.e. the Indo-Burman subduction, as suggested by strike-slip earthquakes. In the latter case, finite displacement would be responsible for the observed curvature of the Sagaing Fault and Red River Fault.