RESEARCH WORK RELATED TO PRESENT
TIME CRUSTAL DEFORMATION
MEASUREMENT IN CHINA
Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, China
China continent crustal motion is still one of the hot spots of studying the intraplate crustal motion and continent dynamics. It undergoes the strong collision of Indian plate and the subduction of Philippine Sea plate and the Pacific plate. The intraplate deformation is very complicated and diversiform. So, it is important to study the crustal deformation around China for lithosphere dynamics and earthquake focal. To monitor and study the crustal motion in China, some nationwide GPS networks and several regional GPS monitoring networks have been set up in the 1990s. Using recent 10-year GPS measurement data of about 1000 sites from these networks and three-campaign GPS measurements provided by the Asia-Pacific Regional Geodetic Project (APRGP), a lot of monitoring results of crustal motion of China and its surrounding regions are obtained during this report time. The monitoring and investigating work of Chinese crustal motion have made great progress. In this report, the research work related to crustal motion measurement of China from 1999 to 2002 is highlighted.
II. DATA COLLECTION AND REDUCTION
In order to monitor and study the crustal motion in China, some nationwide GPS networks and several regional GPS monitoring networks have been set up since 1991. The National (Climbing) key project on basic research “ Investigation on Present-day Crustal Motion and Geodynamics” establishes the first nationwide GPS network named the Crustal Motion Monitoring Network of China (CMMNC). The CMMNC included 24 GPS sites that were situated in each geologic tectonic block in China with an average baseline length 1000 km. Four GPS campaigns in CMMNC were carried in 1992, 1994, 1996 and 1999 respectively. The project “Crustal Motion Observation Network of China (CMONC)” was started in 1997. It mainly relies on GPS technique and consists of a continuously operated state fiducial network of 25 sites, a repeated surveyed (once per year) state basic network of 56 sites The first campaign of CMONC was carried out in August 1998. The fiducial network has been operated continuously since January 1, 1999. Beginning from the early 1990s, several regional GPS monitoring networks about 1000 stations for active tectonic studies were established in China, including Tibet-Himalaya, Tianshan-Tarim, Altun Mountain, Qilian Mountain, Sichua-Yunnan, North China and Fujian coast network, and carried out repeated measurement for several periods between 1991 and 2001 (Zhu et al., 2000a; Wang Q. et al.,2001a; Ma et al., 2001; Cheng et al., 2001). All these GPS measurement data have been processed by GAMIT/GLOBK or GIPSY software and used to monitor present-day crustal motion in China. The estimated accuracy of the horizontal velocity of the sites is shown in (unit: mm/a):
Table 1. Estimated Accuracies of Horizontal Velocity of Sites