HR: 16:00h
AN: NG44A-01 INVITED    [Abstracts]
TI: Recent Progress and Future Direction of Active Monitoring with ACROSS
AU: * Yamaoka, K
EM: kyamaoka@seis.nagoya-u.ac.jp
AF: Graduate School of Environmental Studies, Nagoya University, 1 Furo-cho, Chikusa-ku, Nagoya, 464-8601, Japan
AB: The first ACROSS system for practical use was deployed in Awaji and Tono test site in 1996 by Nagoya University, and JAEA, respectively. Since then the performance of the system has been tested especially for detecting the temporal variation of propagation property of seismic wave. For the first few years an appropriate way of operation for rotational vibrators were looked for. Frequency modulation together with GPS synchronization is found to be fundamentally important technique for the operation of ACROSS vibrators. The first long-term operation test was made at Awaji from January 2000 to March 2001, in which temporal variation of P and S wave are monitored between the source and the receivers that is 1 and 2 km away. In this experiment some changes due to strong ground motion of distant earthquakes were detected. By analyzing the temporal change in S-wave splitting Ikuta and Yamaoka (2004) concluded that the change was due to sudden movement of groundwater in the shallow part of the ground. Another long-term operation test has been continuing at Tono for more than five years. During this operation observation with seismic array was conducted to test the feasibility to detect reflective waves from the boundary of subducting plate in this region. In this experiment Kasahara et al. (2006) identified reflection wave from the boundaries in the deep part of the crust. A new field test is now conducting by JMA, ERI, Shizuoka University and Nagoya University. The target of the test is to detect a temporal variation of reflection wave from the plate boundary. They deployed ACROSS vibrators in two sites and monitor their signal with nation-wide seismic network Hi-net. The principle of ACROSS vibrator, in which signal is generated with a precise synchronization to GPS, is very useful in many sited where we need to know the temporal variation. Based on this concept vibrators with better portability should be developed.
DE: 0935 Seismic methods (3025, 7294)
DE: 4494 Instruments and techniques
DE: 7200 SEISMOLOGY
DE: 7299 General or miscellaneous
SC: Nonlinear Geophysics [NG]
MN: 2007 Fall Meeting