HR: 1340h
AN: NG33B-0175    [Abstracts]
TI: Preliminary study for active monitoring of the plate boundary using ACROSS: Synthetic and observed seismic records
AU: Tsuruga, K
EM: tsuru@tono.jnc.go.jp
AF: Tono Geoscience Center, JNC, Yamanouchi 1-63, Akeyocho, Mizunami, 509-6132 Japan
AU: * Kasahara, J
EM: kasahara.junzo@jnc.go.jp
AF: Tono Geoscience Center, JNC, Yamanouchi 1-63, Akeyocho, Mizunami, 509-6132 Japan
AU: * Kasahara, J
EM: kasahara.junzo@jnc.go.jp
AF: Shizuoka University, 836 Ohya, Suruga-ku, Shizuoka, 422-8017 Japan
AU: Hasada, Y
EM: hasada@tono.jnc.go.jp
AF: Tono Geoscience Center, JNC, Yamanouchi 1-63, Akeyocho, Mizunami, 509-6132 Japan
AU: Kunitomo, T
EM: kunitomo@tono.jnc.go.jp
AF: Tono Geoscience Center, JNC, Yamanouchi 1-63, Akeyocho, Mizunami, 509-6132 Japan
AU: Ikuta, R
EM: ryoya@seis.nagoya-u.ac.jp
AF: Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8602 Japan
AU: Watanabe, T
EM: watanabe@seis.nagoya-u.ac.jp
AF: Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8602 Japan
AU: Yamaoka, K
EM: yamaoka@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, Yayoi 1-1-1 Bunkyo, Tokyo, 113-0032 Japan
AU: Fujii, N
EM: fujii@seis.nagoya-u.ac.jp
AF: Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8602 Japan
AU: Kumazawa, M
EM: smkumaz@ipc.shizuoka.ac.jp
AF: Tono Geoscience Center, JNC, Yamanouchi 1-63, Akeyocho, Mizunami, 509-6132 Japan
AU: Kumazawa, M
EM: smkumaz@ipc.shizuoka.ac.jp
AF: Shizuoka University, 836 Ohya, Suruga-ku, Shizuoka, 422-8017 Japan
AU: Nagao, H
EM: nagao.hiromichi@jnc.go.jp
AF: Tono Geoscience Center, JNC, Yamanouchi 1-63, Akeyocho, Mizunami, 509-6132 Japan
AU: Nakajima, T
EM: takahiro@tono.jnc.go.jp
AF: Tono Geoscience Center, JNC, Yamanouchi 1-63, Akeyocho, Mizunami, 509-6132 Japan
AU: Saiga, A
EM: saiga@eps.nagoya-u.ac.jp
AF: Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8602 Japan
AU: Satomura, M
EM: semsato@ipc.shizuoka.ac.jp
AF: Shizuoka University, 836 Ohya, Suruga-ku, Shizuoka, 422-8017 Japan
AB: ACROSS (Accurately-Controlled Routinely-Operated Signal System) has been developed for active monitoring of a dynamic state in the Earth's structure (Kumazawa et al., 2000). Since November 2004, we have conducted an array observation of ACROSS signals in Tokai area, central Japan, to identify any seismic reflection (and hopefully its temporal change) from the lower crust and/or subducting Philippine Sea plate (Kasahara et al., 2004). In this report, we show the recent results and discuss the relevance of several arrivals of wave groups to underground structures using the theoretical travel times and synthetic waveforms. The frequency-modulated ACROSS signals (10-20 Hz) have been continuously transmitted from the sources located in Toki city, central Japan (Kunitomo et al., 2005) and received at 22 temporal seismic stations at the offset distance of 40-75 km from the source. We define the transfer function between a source and a receiver as a nine-element second-order tensor, Hjk, where j and k denote directional components of the observed displacement and the excitation force, and r, t and v represent the radial, transverse and vertical components, respectively. We recognized the significant wave groups within the travel time ranges of 10-18 and of 15-23 seconds at 54-74 km offset distance through stacking the data for about 60 days. Such wave groups also appear on the records of a Hi-net station at 57.4km by stacking for 30 days (Yoshida et al., 2004). A 2-D velocity structure model was made for our observation area using seismic exploration records across the central Japan (Iidaka et al., 2003). We calculated both travel times by ray tracing method (Fujie et al., 2000; Kubota et al., 2005), and synthetic seismograms by FDM simulation (Larsen and Schultz, 1995). Comparing the observed time series of Hrr and Hzr to the theoretical travel times and synthetic seismograms, we noticed that the wave groups observed at 61-73 km are well corresponding to the theoretical travel times of reflected waves from the bottom of lower crust Moho (PmP) and from the upper boundary of the Philippine Sea plate (PxP). We believe that these results suggest the potentiality for active monitoring of the subtle changes of geophysical properties in the earth's structure using ACROSS signals in future. Acknowledgements: We appreciate the permission to use the seismic waveform data provided by the Research Group for Seismic Expedition in Central Japan.
DE: 7200 SEISMOLOGY
DE: 7218 Lithosphere (1236)
DE: 7240 Subduction zones (1207, 1219, 1240)
SC: Nonlinear Geophysics [NG]
MN: Fall Meeting 2005