OECD/NEA WS 1/8 EARTHQUAKE RELATED PROJECTS IN NIED, JAPAN Yoshimitsu Okada NIED (National Research Institute for Earth Science and Disaster Prevention), Japan Abstract Earthquake related projects in NIED were originated from the work to develop a very deep borehole seismic observatories surrounding Tokyo Metropolis. After the occurrence of Kobe earthquake in 1995, NIED has started two big projects. One is to construct 3-D Full Scale Earthquake Testing Facility for earthquake engineering study and the other is to construct nation-wide seismic network of high-sensitivity, strong-motion, and broadband seismographs. At the same time, the projects aiming direct contributions to the society were newly started such as the study to develop real-time seismic information system and the research on mapping of predicted strong-motion. These projects are conducted in NIED with a close cooperation each other. Overview of earthquake related projects in NIED Since its establishment in 1963, National Research Institute for Earth Science and Disaster Prevention (NIED) has conducted earthquake related projects as one of the most important tasks of the institute. At the first stage, main efforts were concentrated to the Kanto and Tokai regions, central Japan. The Kanto-Tokai area has specialty both in the scientific and social aspects. According to the collision of the Izu Peninsula against continental plate, Kanto and Tokai regions are threatened by the situation that giant trench-type earthquakes are not generated at offshore but right under our foots. Moreover, both regions are densely populated and are bearing quite important roles in politics and economics of Japan. In 1969, NIED started a project, Research on Seismic Activities in the Southern Metropolitan Area,
OECD/NEA WS 2/8 in which a 3,000m-class deep borehole seismic observation system was developed to realize highly sensitive microearthquake observation in a densely populated urban area (Takahashi, 1982). The system was installed at three sites surrounding Tokyo, Iwatsuki (3,510m), Shimohsa (2,330m) and Fuchu (2,781m). As its background, the importance of Tokyo observation had been emphasized in the National Earthquake Prediction Program which wad started in 1965 and southern Kanto region was designated as the Area of Intensified Observation in 1970 by the Coordinating Committee for Earthquake Prediction. Later, by close-up of the imminence of Tokai earthquake, Tokai region was also designated as the Area of Intensified Observation in 1974. Further a part of Kanto-Tokai area was designated as the Area under Intensified Measures against Earthquake Disaster in 1979. Corresponding to such an environment, NIED started another project, Research on Crustal Activities in the Kanto-Tokai Area, in 1978 in which a dense shallow borehole network for microearthquake and crustal tilt observation was constructed covering the both of Kanto and Tokai regions (Hamada et al., 1985). In this project, the first fixed-point GPS network in the world was also constructed in 1988 (Shimada et al., 1990). These two projects have produced many outputs such as delineation of the plate configuration in this complex area (Kasahara, 1985; Ishida, 1992) and the findings of a rocked zone in Tokai area and its seismic quiescence in recent years (Matsumura, 1997). GPS observation provided important data to interpret the earthquake swarm activity and the submarine eruption at eastern off Izu Peninsula in 1989 (Okada and Yamamoto, 1991). In 2001, these two projects were unified to a project, Research on Seismic Activities in the Kanto-Tokai Area, and further investigation is expected for forthcoming Tokai earthquake and the earthquake just beneath Tokyo metropolitan area. In 1978, at the same time with the Kanto-Tokai project, another project, Research on Mechanism of Earthquake Generation, was also started to investigate the basics of inland earthquakes through in-situ stress measurement by hydro-fracturing method (Tsukahara and Ikeda, 1987). Later, another project for basic study, Fundamental Research on Earthquakes and Earth s Interior Anomaly (FREESIA), was added in 1994 (Fukuyama et al., 1996). The aim of this project was to investigate the source process using an observation network of broadband seismographs. The occurrence of the Kobe earthquake of 1995 affected so much the trend of earthquake related projects in NIED. Several big projects listed below were newly started under the policy of the Headquarter for Earthquake Research Promotion, which was established by Japanese Government after the Kobe earthquake. (1) 3-D Full Scale Earthquake Testing Facility (E-defense) In order to develop safety building structure, the 3-D large shaking table (E-defense) is under construction and related research projects were started.
OECD/NEA WS 3/8 (2) Research on Earthquake Disaster Mitigation (EDM) Aiming for integration of science, technology and social engineering studies, a research team for earthquake disaster mitigation, EDM, was transferred to NIED in 2001 from RIKEN. (3) Operation of seismic networks (Hi-net, F-net, K-NET and KiK-net) A large number of seismographs were newly installed covering the whole of Japan. The data are merged to those from existing networks and are provided to the public under a fully open policy. (4) Development of real-time issue and distribution system of earthquake information As a way to utilize seismic data for hazard mitigation, a real-time earthquake information system is developed to issue quick alarms before the arrival of S-wave. (5) Research on the mapping of predicted strong-motion To complete a nation-wide probable shaking map and the one estimated by scenario earthquakes, various techniques are developed to estimate strong motions and represent them on a map. These projects are closely related each other. For example, soil condition data or velocity logging data obtained at boreholes as a by-product of the project (3) become quite useful information to estimate surface strong motions in the project (5). In the following sections we introduce two biggest projects in NIED, (1) E-defense and (3) Operation of seismic networks. Figure 1. On-going earthquake related projects in NIED Experimental study O bservational study Social study Earth Science Disaster Prevention M echanism of Earthquake Generation E-defense Kanto-Tokai Real-time M apping Predicted Strongmotion EDM Operation ofseism ic Network Construction of 3-D Full Scale Earthquake Testing Facility (E-defense) Learning from the lessons of the Kobe earthquake, NIED planned to construct the world s largest three-dimensional (3-D) full-scale shaking table in Miki city near Kobe which is now nicknamed as
OECD/NEA WS 4/8 E-Defense. It will be able to simulate the processes of destruction of structures under the condition of real strong earthquake motions. By testing real-sized structures to collapse it will facilitate to calibrate and validate our earthquake resistant design capabilities. The size of E-Defense is 20m x 15m and its basic performances are maximum loading capacity of 1,200 tons, maximum velocity of 200 cm/s and maximum displacement of 2m p-p for horizontal excitation and maximum velocity of 70 cm/s, maximum displacement of 1m p-p for vertical excitation to realize destructive ground motion. The construction work of E-Defense has begun at Miki City in early 2000, and will be completed at the beginning of 2005. The manufacturing, assembling and installing of actuators, oil-pressure supply system and other major parts of shaking table are borne by the Mitsubishi Heavy Industry. Figure 2. Concept of E-defense Concerning the utilization of E-Defense, there are many subjects which NIED should make clear before the operation of the facility becomes possible. In order to solve these subjects, NIED is actively investigating the practical research themes as follow, 1) Establishment of utilization and wide area network systems, 2) Development of 3-D ground motion database for input motion of E-Defense and a simulation system for the 3-D shaking table, and 3) Test and analysis of reinforced concrete structures, soil-pile-structure systems and conventional wooden structures for using E-Defense. Further, many domestic research centers, universities, independent administrative institutions, private companies are involved in a collaborative research. E-Defense is a very large scale and high performance testing facility in the world and should be operated as the facility of internationally common use. For the international collaboration and the dissemination of the research results, E-Defense Network ( ED-net ) will be also constructed until the
OECD/NEA WS 5/8 completion of E-Defense. ED-net will connect major earthquake engineering research organizations in the world through a high performance Internet line. We hope that E-Defense and ED-net will be situated to one of the cooperative research organization for the earthquake disaster mitigation in the world. Figure 3. Actuators of E-defense (at Miki City) Construction of nation-wide seismic networks (Hi-net, F-net, K-NET and KiK-net) After the Kobe earthquake, we learned that a systematic observation system of the ground motion is lacked in Japan. NIED planned to install 1,000 strong-motion seismographs covering the whole of Japan (Kinoshita, 1998). The network is called K-NET (Kyoshin network), where Kyoshin is a Japanese word to mean strong-motion. At the same time, a new national plan called KIBAN project has started to drastically improve seismic observation system in Japan. To construct dense and uniform networks covering the whole of Japan, it was designed to set up 1000 stations with an average spacing of 20km for high sensitivity and strong motion seismographs, and 100 stations with an average spacing of 100km for broadband seismograph. The construction and operation of these networks was charged to the NIED based on the experience in the Kanto-Tokai observation network. A large number of seismographs of several kinds were installed to realize this plan. High sensitivity seismographs were installed in a borehole of 100-200 m depth in standard to assure high sensitive microearthquake observation at each site. The new network consisting of 696 high sensitivity stations is called Hi-net (High sensitivity seismograph network), which results a network of nearly 1250 high sensitivity stations in whole Japan if we include pre-existing stations. On the other hand, broadband seismographs were installed in a vault of 30 to 40 m long to assure stable operation at each site. The new
OECD/NEA WS 6/8 network consisting of 71 broadband stations is called F-net (Full-range seismograph network), which results a network of nearly 100 broadband stations in whole Japan if we include pre-existing stations. At most of the Hi-net stations strong-motion seismographs are also equipped both at the bottom of the borehole and on the ground surface. The network of 659 stations with such an uphole/downhole pair of strong-motion seismographs is called KiK-net (KIBAN Kyoshin network). The KiK-net made it possible to evaluate the effect of soil conditions of surface layers upon the amplitudes of seismic waves by comparing the strong motions at depth and at the ground surface. On the other hand the number of the K-NET stations is increased to 1034, where all the station numbers above are as of April 2003. In total, NIED is now operating nearly 1900 stations of several kinds of seismographs covering the whole of Japan. Figure 4. Configuration of Hi-net / KiK-net station Since October 1997, high-sensitivity data from the Hi-net as well as those from pre-existing seismic networks operated by various institutions have been transmitted to and processed in a unified manner by the Japan Meteorological Agency. Hi-net data are not only utilized to monitor the seismic activities in
OECD/NEA WS 7/8 and around Japan, but also shared to university group in real time by using satellite communication for their research works. At the same time, the data are collected by NIED, stored in their database system, and distributed to the public under a fully open policy (Okada et al., 2004). High quality data produced by these networks are not only used for monitoring of seismic activity but are providing a plenty of seeds for interesting researches. Using Hi-net, Obara (2002) found a phenomenon of non-volcanic deep tremor associated with subduction of the Philippine Sea plate over a length of 600km in southwest Japan. Using F-net, Kubo et al. (2002) analyzed maximum horizontal stress directions in and around Japan and local stress field in the focal zone of the western Tottori earthquake of 2000 (M7.3). Using K-NET and KiK-net, Honda et al.2004 analyzed rupture process of the Tokachi-oki earthquake of 2000 (M8.0). Figure 5. Distribution of peak accelerations at (a)100-200m depth and (b)on the ground surface detected by K-NET and KiK-net associated to the western Tottori earthquake (M7.3) of October 6, 2000 References Fukuyama, E., M. Ishida, S. Hori, S. Sekiguchi, and S. Watada, Broadband seismic observation conducted under the FREESIA project, Rep. Natl. Res. Inst. Earth Sci. Disas. Prev., 57, 23-31 (in Japanese with English abstract), 1996.
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