Jointly Inversing the Plate Driving Forces on the Boundaries Around Sichuan-Yunnan Area Using GPS Measurements of the Crustal Movement Observation Network of China and the Principal Stress Orientation Data of China Area

Considering the rationality and the physical significance of two different kind data including geodesy displacements and main stress orientations with different time scales used simultaneously in inversion,the following views are put forward.(1) The GPS elevation data still have not enough precision for the driving forces acting at the boundaries constraint and lack traditional geodesy observation data(like leveling data).(2) The surveying points that reflect the stress size of deep crust are too few and the depth are not deeper than 5km now.In the meanwhile,the observation data of stress orientation are accumulating in a very high speed.Although the single principal stress orientation does not contain the size information of stress,the principal stress orientations of multiple points contain the relative size information of driving forces acting at the boundaries.(3) Not only the traditional geodesy displacements but also the GPS displacements are the displacement changes(or displacement velocity) over some time and are not the total displacements from the initial state required by the dynamic models,so the difficulty in physics interpretation is obvious when only using displacement data of the study area to inverse the driving forces acting at the boundaries without considering the simplicity in mathematical algorithm.(4) Despite the two different kinds of data with different time scales,the principal stress orientation especially the orientation that reflects the change trend of the area has the changelessness for a very long period,the two different kinds of data can be used jointly if the displacement data has the trend character.(5) The use of two different kinds of data for inversing the driving forces acting at the boundaries not only enriches the observation data required by inversion but improves the geodesy physics interpretation of the inversion results acquired by displacement data with the help of the data of the principal stress orientation.Employing the GPS displacement data and the principal stress orientation data of China area,the research of joint inversion of the plate driving forces acting on the boundaries around Sichuan-Yunnan area is made and a whole set of schemes is presented.After briefly introducing tectonic structure and tectonic kinematic feature of Sichuan-Yunnan area,the rationality and physical sense of different observations simultaneously using for inversion are discussed.Then the inversion com-putation of elastic finite element is made with the forces on the boundary and relative weight ratio as parameters to be inversed using displacement data of nine stations surveyed from 1998 to 2000 and the ten principal stress orientation data observed before 1986.Meanwhile,the kinematic feature of active fracture is taken into account.The results show that the present main driving forces of structure motion of Sichuan-Yunnan area are still from the collision of Indian plate with Eurasian plate and the extrusion effect of Philippine plate can not be ignored.This result demonstrates the succession feature of structure motion of this area nowadays.