中国大陆现今构造变形GPS观测数据与速度场

GPS DATABASE AND VELOCITY FIELD OF CONTEMPORARY TECTONIC DEFORMATION IN CONTINENTAL CHINA

利用 1991— 1999年间 36 2个全球定位系统 (GPS)测站的观测资料 ,初步获得了中国大陆及周边地区现今地壳水平运动的统一速度场。该速度场主要涵盖青藏高原 ,天山 ,塔里木、川滇 ,河西走廊 ,福建东南沿海等重要构造活动区 ,测定精度总体优于 2～ 3mm/a ,速度场站点的分布和测定精度基本上满足中国大陆现今构造变形和动力学研究的需求。现代大地测量第一次比较全面、定量地展示出中国大陆在周边板块作用下大幅度构造变形的图像 ,为模拟大陆岩石圈动力过程提供了基础性的运动学约束条件。

Global Positioning System (GPS) provides a powerful means to directly measure kinematic pattern of present\|day crustal deformation. Previous GPS network within China and its vicinity has been originally designed to address local problems without attempting to solve the large\|scale deformation of continental Asia, and therefore the measurement results can not be patched together seamlessly, due to different data analysis strategies involved, to yield an uniform velocity field. The only realistic approach on a large\|scale GPS solution to date is to merge observation data from different regional network into a coherent solution. We adopt the following strategy to deduce disparate data sets observed at different epochs and different regions into an integrated solution of station motions on a common reference frame at continental scale. In the first step, regional GPS data were combined with continuous tracking data from IGS stations using the GIPSY/OASIS\|II software. For data observed between 1991 and 1994, we use a global solution strategy in which parameters associated with GPS satellite orbits are estimated together with station coordinates, phase ambiguities and other modeling station clocks and troposphere behavior based on a well\|distributed set of global IGS stations. For data observed from 1995 to 1999, a regional solution strategy was adopted, using JPL's orbits and satellite clocks. Only a subset of IGS stations was used. For all daily solution we follow a 'non\|fiducial' strategy. A loosely constrained solution for the station positions is obtained each day. In the second step, all of the loosely constrained solutions are transformed into the ITRF97 reference frame by estimating the seven\|parameter transformation that minimizes misfits of the common stations between them. The quality of transformation depends on accuracy of the coordinates and velocities of the reference stations, and on their geographic distribution. Therefore we select those stations that have at least five\|year data span in Asia as well as well\|distributed global stations. In the final step, daily solutions are combined together to determine station velocities and station coordinates at epoch 1995 by the standard weighted least squares adjustment from which an integrated velocity field can be derived. Furthermore we define an Eurasia\|fixed reference frame by subtracting the Eurasia plate movement predicted by the NNR\|NUVEL\|1A model from GPS station motion on the ITRF97 reference frame. The residual station velocities are in the sense of deformation relative to stable Eurasia continent. The aggregate velocity solution represents synthesis of independent geodetic networks available throughout continental Asia, and provides the most coherent image of ongoing crustal deformation in this region to date. The implications on geodynamics are discussed in the companying papers.