9727652 Bilham This project is aimed at understanding the details of the collision between two continental plates - India and Asia. GPS (Global Positioning System) geodesy will be used to measure the motion of some 100 points distributed throughout parts of the collision zone, between the northern plains of India, and the Tarim basin north of Tibet. In particular, the P.I.s are interested in the unique processes that occur beneath southern Tibet and the Greater Himalaya because these appear to be close to the nucleation zone of great earthquakes whose future recurrence will be disastrous to the populations of northern India and Nepal. The study builds on their 1997 finding that the Himalaya are contracting north-south at a rate of 21+-3 mm/year, but that this contraction is largely concentrated in a zone less than 100 km wide. It appears that Tibet may also be contracting at 5-10 mm/year. Observations indicate it is probable that Himalayan contractionis largely elastic (strain energy developing for future great earthquakes), and that Tibetan contraction at depth is largely plastic (driving east-west expansion of the plateau and surface seismicity). The measurements the P.I.s propose are designed to provide constraints on the physics underlying these processes, and details of the transition zone between them. ***
