First Crustal Deformation Monitoring Center, China Seismological Bureau, Tianjin 300180, China
The scientific objective of the Crustal Movement Observation Network of China (abbreviated as CMONOC) is taking the earthquake prediction as the dominant, giving consideration to the need of geodesy and providing services to the fields of wide-area differential GPS, meteorology and satellite-borne synthetic aperture radar interferometry, etc.
The key techniques for the engineering construction of CMONOC are the high-precision and high-stability observation, the large-amount collection of data, and the rapid and accurate real-time data processing.
The total engineering of CMONOC consists of four parts: the fiducial network, the basic network, the local network and the system for data transmission, data processing and data analysis.
As the principal frame of CMONOC, the fiducial network consists of 25 GPS stations for continuous observation. VLBI and SLR observations are also made at some of the stations. With an average distance of about 700 km between the adjacent stations, the main function of the fiducial network is to monitor the tectonic movement of the first-order blocks in Chinese mainland. The new fiducial stations are all built on the bedrocks. The observation accuracies are ±1.3 mm for the annual length variation of GPS baseline between the adjacent fiducial stations, ±1.5 mm for the annual variation of baseline between the adjacent VLBI stations, ±2.1 cm for the determination of absolute coordinates of the fixed SLR stations, and ±0.8-4.9μGal for the absolute gravity survey. The fiducial network was put into operation on April 1, 2000.
The basic network is composed of 56 GPS stations for regular repeated measurement. As a complement to the fiducial network, the basic network is mainly used to monitor the crustal deformation in and between the first-order blocks. The basic stations are uniformly arranged together with the fiducial stations with an average distance of about 350 km. Two measurements of basic network were carried out both in 1998 and 2000 with the accuracy of less than ±3 mm for the horizontal component and less than ±10 mm for the vertical component.
The local network is constituted by 1000 GPS stations (1056 stations including the basic network) for irregular repeated measurement. They are arranged in ten monitored areas. About 700 of them are concentrated along the principal tectonic and seismic zones to monitor the activity status of the zones for earthquake prediction; about 300 of them are uniformly arranged over the whole country as a complement to the fiducial and basic networks to monitor the movements in the major blocks. The local network was established in the August of 1998, the first measurement was carried out in 1999 and more than 800 stations were remeasured in 2001. The calculated results indicate that the observation accuracy is less than ±3 mm for the horizontal component and less than ±10 mm for the vertical component.
The data system consists of a data center and three data-sharing subsystems. The data center is responsible for network operation and management, routine data processing and analysis, which are directly applied to earthquake prediction and disaster mitigation. The data center also provides the basic data to each data-sharing subsystem and the related ministries and commissions. The data-sharing subsystems mainly provide service to the research in astrogeodynamics and the Asia-Pacific Space Geodynamics Program, as well as the national geodetic control net and the fundamental surveying and mapping. The construction of the data system was totally accomplished in 2000. Its principal technical indexes are 310 Mb daily for data collection, 50 Gb for on-line data storage and 220 stations daily for data processing.
By the end of 2000, tested and checked by the State Acceptance Committee, the complete network engineering reached and surpassed the designed requirements in various technique indexes and was put into operation.
Covering an area of 95% in Chinese mainland, CMONOC has raised the accuracy for traditional measurement of crustal movement in China by three orders of magnitude and the observation efficiency by tens times. It has preliminarily realized the quasi-instantaneous monitoring over the whole country and fundamentally improved the manner and function of dynamic monitoring on the surface of the Earth. It has heightened the ability to predict great earthquake in China. China Seismological Bureau has already used the GPS-observed data in the annual seismologic consideration and better results have been obtained in the long and medium-term earthquake predictions. It has increased the accuracy of the geodetic control network and helps to refine the datum for surveying and mapping. It has also significantly promoted the state key basic researches. The “Current Crustal Movement and Geodynamic Research” in the China Climbing Project and the “Mechanism and Prediction of Continental Earthquake” in the State Key Basic Research Project have both regarded the CMONOC as the principal supporting condition for project establishments and further studies. The observation of the network has provided significant basic data for these projects.
In the past three years, the CMONOC operates normally and large amounts of observed data have been obtained. Seven fiducial stations have been used as IGS stations and their data have been used for the international exchange. The data obtained from the network have been used in the scientific studies and more than one hundred papers have been published. The following map of horizontal crustal movement rate in Chinese mainland is based on the data from the CMONOC. Up to now, this is the map drawn with the most detailed, accurate and homogeneous data and by the most strict processing method.
With the progresses achieved in the science and technology and the national economy, especially the development in the West China, the existed CMONOC can not meet the need in various fields. The Chinese geodesists are preparing to make a continuation for it. The fiducial stations will be increased to 260 and the local stations to 2000 in the next several years. Cooperated with IGS, CMONOC will establish the mirror image of IGS data in China in order to provide WEB and FTP services of GPS data through Internet.
Fig.1. Map of horizontal crustal movement rate in Chinese mainland
(from Wang Min in the Data Center of CMONOC and to be published)
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