HR: 1340h
AN: NG33B-0176    [Abstracts]
TI: Monitoring Experiment in Tokai, Japan : ACROSS source designed for a phased array
AU: * Yamaoka, K
EM: yamaoka@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo, 113-0032 Japan
AU: Watanabe, T
EM: watanabe@seis.nagoya-u.ac.jp
AF: Reserch Center for Seismology and Volcanology, Graduate School of Environmental Studies, Nagoya University, 1 Furo, Chikusa, Nagoya, 464-8602 Japan
AU: Fujii, N
EM: fujii@seis.nagoya-u.ac.jp
AF: Reserch Center for Seismology and Volcanology, Graduate School of Environmental Studies, Nagoya University, 1 Furo, Chikusa, Nagoya, 464-8602 Japan
AU: Ikuta, R
EM: ryoya@seis.nagoya-u.ac.jp
AF: Reserch Center for Seismology and Volcanology, Graduate School of Environmental Studies, Nagoya University, 1 Furo, Chikusa, Nagoya, 464-8602 Japan
AU: Miyajima, R
EM: miyajima@seis.nagoya-u.ac.jp
AF: Reserch Center for Seismology and Volcanology, Graduate School of Environmental Studies, Nagoya University, 1 Furo, Chikusa, Nagoya, 464-8602 Japan
AB: The Tokai district in Japan is the place where a large interplate earthquake is regarded as being impending. Japanese research group for active monitoring are planning to monitor the propagation property of seismic wave in this area using active seismic sources. As a part of the project we are deploying ACROSS vibrators as well as a seismic array in this area. The vibrator we use is originally deployed in another place as a set of four rotational sub-vibrators, which is designed to generate linear acceleration in any direction. As a switching operation method are developed to generate linear acceleration in any direction with a linear combination of the signals of two opposite rotation direction, we use four sub-vibrators as a phased array in the Tokai monitoring experiment. The area we are monitoring has many important aspects for a test site of monitoring experiment. The area is the edge of the source region of the interplate earthquake, so called the Tokai earthquake, where changes are most likely to occur in the preparation stage of earthquakes. A strong reflector at the interface between subducting and overriding plate is detected with explosion experiments. The vibrators and array are located to receive the reflection with good efficiency. Our estimation shows that one-week stacking is enough to detect one percent change in amplitude. A long-term slow slip and sporadic slow slips are observed on the plate interface. The long-term slip has been continuing since 2000, which is revealed by GPS network (GEONET). Sporadic slow slips with durations of several days are detected by tilt and strain meters that are deployed in this area. Low frequency earthquakes or tremors are often observed near the plate interface, whose source is regarded as a movement of fluid. These phenomena can cause the variation of seismic propagation property, especially reflection at the plate interface. In the source site, change in the elastic or inelastic property of the ground around the source is monitored. The experiment mede in Awaji test site shows the importance of monitoring of the source movement. The actual movement of the source can be altered by environmental condition such as temperature, rainfalls or groundwater level. The site we are deploying the source is in the observatory belonging to Nagoya University. It has a horizontal vault of more than 100 m deep in hard rock, where seismometers and strainmeters are already deployed. Groundwater levels are also monitored in deep boreholes. Using these data together with additional seismometers environmental monitoring around the source will be made to calibrate the radiation wave. We start the monitoring experiment in 2006 together with other ACROSS sources being operated by JNC (Japan Nuclear Cycle development Institute) and MRI (Meteorological Research Institute). The nation-wide seismic network (Hi-net) is also used for monitoring. * ACROSS stands for 'Accurately Controlled Routine Operated Signal System'. An ACROSS vibrator radiates continuous elastic wave of sinusoidal signal for monitoring the earth's crust.
DE: 0935 Seismic methods (3025, 7294)
DE: 0994 Instruments and techniques
DE: 4494 Instruments and techniques
DE: 7215 Earthquake source observations (1240)
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
SC: Nonlinear Geophysics [NG]
MN: Fall Meeting 2005