DEVELOPMENT OF SEISMOLOGICAL OBSERVATION
AND INTERPRETATION IN CHINA IN THE TURN
OF THE CENTURIES: ESTABLISHMENT OF THE
CHINA DIGITAL SEISMOLOGICAL
LIU Ruifeng1), WU Zhongliang3, 4), YIN Chaomin2), CHEN Yuntai1),
CHEN Zhangli2) and ZHUANG Cantao3)
1) Institute of Geophysics, China Seismological Bureau, Beijing 100081, China2) China Seismological Bureau, Beijing 100036, China3) Center for Analysis and Prediction, China Seismological Bureau, Beijing 100036, China4) College of Earth Sciences, Graduate School of the Chinese Academy of Sciences, Beijing 100036, China
In the turn of the centuries, there is a significant development in seismological observation and interpretation in China. The establishment of China Digital Seismological Observational Systems upgraded the capability of the seismological observation and interpretation in this seismically active country. The significance of this advancement is regarded as to be comparable to the establishment of the Chiufeng (Jiufeng) Seismic Station in 1930 which is the first seismological observatory installed and managed by Chinese seismologists, and the seismological investigation of the 1966 Xingtai, Hebei, earthquake which is the beginning of nation-wide earthquake prediction study in China leading to the successful prediction of the 1975 Haicheng, Liaoning, Ms7.3 earthquake, an ice-breaking and unique successful strong earthquake prediction in human history.
The Sino-US cooperative China Digital Seismograph Network (CDSN) was the first national digital seismograph network in China. It was installed in the 1980s and is now operating as a partner of the Global Seismograph Network (GSN). From 1996 to 2000, supported by the central government and local governments, the China Seismological Bureau (CSB) launched a national project of updating the seismological observation facilities into digital broadband seismological observation systems. The new generation of China Digital Seismological Observational System includes the following four parts.
I. CHINA NATIONAL DIGITAL SEISMOGRAPH NETWORK (CNDSN)
The newly installed China National Digital Seismograph Network(CNDSN) has 47 real-time seismic stations including the 11 CDSN stations as partners, as shown in Figure 1a. The instruments used in these stations include the Swiss made STS-2 broadband seismograph and the Chinese made JCZ-1 very-broadband (VBB) and very-long-period (VLP) seismographs and the Chinese made CTS-1 broadband (BB) seismograph. Waveform data are transmitted to the data center in real-time through satellite links.
Fig.1a. Distribution of real-time digital seismic stations in the China National Digital Seismograph Network(CNDSN).
Triangles: stations using STS-2 seismograph;
Circles: stations using JCZ-1 seismograph;
Squares: stations using CTS-1 seismograph.
As auxiliary stations, there are also 28 non-real-time seismic stations in the network, as shown in Figure 2. The instrument used in these stations is the Chinese made FBS-3 broadband (BB) seismographs. Waveform data are transmitted to the data center through a dial-up mode in some stations, while other stations mail the recording CDs to the data center.
The JCZ-1 very-broadband (VBB) seismograph has a flat velocity response from 300s to 20Hz, with a sampling rate 50sps. The JCZ very-long-period (VLP) seismograph has a flat acceleration response from 3000s to 300s, with a sampling rate 1sps. The dynamic range of both instruments is 140dB. This kind of instrument is installed at 10 stations, as shown in Figure 1a. The CTS-1 broadband (BB) seismograph has a flat velocity response from 120s to 20Hz, with a sampling rate of 50sps. The dynamic range is 140dB. It is installed at 27 stations, as shown in Figure 1a. The well-known STS-2 instruments are installed at 10 of the CDSN stations excepting Lanzhou (LZH), as shown in Figure 1a. As an example of the seismic recordings, Figure 1b shows the waveforms of the November 14, 2001, western Kunlun Mountain Pass, border of Qinghai-Xizang Plateau (Tibetan Plateau), MW7.8 earthquake, recorded at some of these real-time stations.
HTA(Hotan) TIA(Tai'an) HEH(Heihe) HHC(Hohhot)
Fig.1b. Seismograms of the November 14, 2001, western Kunlun Mountain Pass, MW7.8 earthquake as recorded at some national digital seismograph stations.
The FBS-3 broadband (BB) seismograph has a flat velocity response from 20s to 20Hz, with a sampling rate of 50sps. The dynamic range is 90dB. This instrument is installed in the non-real-time stations.
One of the missions of the National Digital Seismograph Network is to perform fast source parameter determination for the earthquakes in the territory of China over magnitude 4.5, the earthquakes in the vicinity of China over magnitude 6.0, and the earthquakes worldwide with magnitude over 7.0. The network itself has the ability to monitor the seismic events down to magnitude 3.5 within the Chinese mainland.
Fig.2. Distribution of non-real-time digital seismic stations in the national network.
II. CHINA REGIONAL TELEMETERED DIGITAL SEISMOGRAPH NETWORKS(CRTDSN)
Supported by both the central government and the local governments, 21 China Regional Telemetered Digital Seismograph Networks(CRTDSN) are installed to enhance the capability of monitoring regional seismicity and conducting studies on regional seismo-tectonics. The whole regional network includes 267 digital seismic stations, as shown in Figure 3 (Seismic Networks in Taiwan is not included in this map and is not introduced in this report. Digital seismic observation in Taiwan also has a significant development in recent years. Cooperation between the two sides of the Taiwan Strait developed fast in many aspects for seismic hazard mitigation.) It can be seen that these networks basically cover the north-south seismic belt, the north-China seismic belt, the north Xinjiang seismic belt, and the south-eastern China coast, aiming to the reduction of seismic disasters in these densely populated and seismically active areas. Most of the stations installed the Chinese made FBS-3 broadband (BB) seismographs, while other stations installed the Chinese made FSS-3 short-period (SP) seismographs. The FSS-3 SP seismograph has a flat velocity response from 1s to 20Hz, with a sampling rate of 50sps and a dynamic range of 90 dB to 120 dB.China Regional Telemetered Digital Seismograph Networks are responsible for the fast source parameter determination for earthquakes over magnitude 3.5 in and around the network coverage, and the earthquakes over magnitude 6.0 within the Chinese mainland. They have the ability to monitor the seismic events down to local magnitude 1.5 within the network coverage. Sponsored by the provincial seismological bureaus, the data centers of these networks compile regional earthquake observational reports, and provide seismological data for the study and application of earthquake prediction and engineering seismology.
Fig.3. China Regional Telemetered Digital Seismograph Network (CRTDSN).
III. THE CAPITAL CIRCLE AREA SEISMOLOGICAL NETWORK
The Capital Circle Area which includes Beijing, Tianjin, and the adjacent provinces is an important area in the reduction of seismic disasters in China. In this area there had occurred the 1679 Sanhe-Pinggu earthquake, 30km eastern of Beijing, with magnitude estimated over 8, and the 1976 Tangshan MS7.8 earthquake, causing 24,0000 people died. In recent years the economy and urbanization of this area grows up fast. As the capital of China, Beijing acts as the center of economy, culture, and politics of China and an international modernized megacity. In 2008 Beijing will host the Olympic Games.
To enhance the capability of seismological monitoring and earthquake emergency response in this area, from 1999 to 2001, a densely deployed real-time digital seismograph network was installed with the support from both the central government and the local governments of Beijing City, Tianjin City, and Hebei Province. The network has 107 real-time digital seismic stations, with the spacing between stations about 50 km. Jointly managed by the Center for Analysis and Prediction of the China Seismological Bureau, the Institute of Geophysics of the China Seismological Bureau, the Beijing City Seismological Bureau, the Tianjin City Seismological Bureau, and the Hebei Province Seismological Bureau, this network is responsible for the monitoring of seismicity and earthquake emergency response in the Capital Circle Area and its vicinity. The network has the capability to monitor seismic events over local magnitude 1.5 in Beijing, seismic events over magnitude 2.0 in the Capital Circle Area, and earthquakes with magnitude over 3.5 within the whole northern China area. It has the ability to issue the fast determination of the source parameters of an earthquake over magnitude 3.0 in Beijing and an earthquake over magnitude 3.5 in the Capital Circle Area within 10 minutes.
Fig.4. The Capital Circle Area seismological network.
IV. DATA CENTER OF THE CHINA NATIONAL DIGITAL SEISMOGRAPH NETWORK
Data Center of the China National Digital Seismograph Network has two parts, one in the Center for Seismic Disaster Reduction of the China Seismological Bureau, being responsible for the fast determination of source parameters and the data service for the earthquake emergency response, the other in the Institute of Geophysics of the China Seismological Bureau, being responsible for seismological interpretation, improvement of the source parameter determination, quality control, and domestic/international data exchange service.The data center of the National Digital Seismograph Network compiles and publishes three bulletins/reports for data exchange:
(1) The monthly Observational Report of the China National Digital Seismograph Network, including the phase reading data from the 75 seismic stations (47 real-time and 28 non-real-time) within the national digital seismograph network;
(2) The monthly Observational Report of the China Digital Seismic Stations, including the phase reading data from the 24 seismic stations which have been participating in the global international data exchange for a long time. These data are sent to the International Seismological Center (ISC) in Europe and the National Earthquake Information Center (NEIC) in USA regularly in electronic form;
(3) The Annual Bulletin of Chinese Earthquake Catalogues and Focal Mechanism Solutions of Strong and Intermediate-Strength Earthquakes.Source parameters determined include the location, origin time, and ML, MS, and mb magnitudes. Magnitude is determined using the simulation scheme, i.e., to simulate the ‘standard' seismograph using digital filters and to simulate the ‘standard' procedure of measurement using digital waveforms. This scheme guarantees the consistency of the magnitude measurement. Meanwhile, moment tensor inversion is performed on the earthquakes with magnitude over 5.0 within the Chinese mainland. Data service is through Internet via http://www.csndmc.ac.cn.