HR: 09:00h
AN: S31C-05    [Abstracts]
TI: Evaluation of a dense seismic array for acquisition of high quality data in the ACROSS observation
AU: * Tsuruga, K
EM: tsuru@tono.jnc.go.jp
AF: Tono Geoscience Center, JNC, 1-63 Yamanouchi, Akeyocho, Mizunami, Gifu, 509-6132 Japan
AU: Kunitomo, T
EM: kunitomo@tono.jnc.go.jp
AF: Tono Geoscience Center, JNC, 1-63 Yamanouchi, Akeyocho, Mizunami, Gifu, 509-6132 Japan
AU: Hasada, Y
EM: hasada@tono.jnc.go.jp
AF: Tono Geoscience Center, JNC, 1-63 Yamanouchi, Akeyocho, Mizunami, Gifu, 509-6132 Japan
AU: Kumazawa, M
EM: mkz@tono.jnc.go.jp
AF: Tono Geoscience Center, JNC, 1-63 Yamanouchi, Akeyocho, Mizunami, Gifu, 509-6132 Japan
AU: Shigeta, N
EM: taka@tono.jnc.go.jp
AF: Tono Geoscience Center, JNC, 1-63 Yamanouchi, Akeyocho, Mizunami, Gifu, 509-6132 Japan
AU: Kasahara, J
EM: kasahara.junzo@jnc.go.jp
AF: Tono Geoscience Center, JNC, 1-63 Yamanouchi, Akeyocho, Mizunami, Gifu, 509-6132 Japan
AB: ACROSS is an active monitoring methodology to detect any subtle temporal change of physical properties in the Earth's interior. We demonstrate the potentiality of the ACROSS observation with a dense sensor array. We have conducted a dense seismic array observation at the distance of 1 km from the ACROSS source since 2003. The array is composed of 36 three-component velocity seismometers buried at 1.8 m deep in an area 25 m square. All the data are recorded accurately referring to a GPS clock. We derived and analyzed a transfer function (TF) from the source to a receiver by the following steps: (1) evaluating a force vector as source characteristics, (2) converting the observed data to the displacement vectors by incorporating all the corrections of the instruments, (3) stacking the observed data for an enough time to suppress the temporal noise, (4) extracting ACROSS signal and evaluating noise level, (5) representing TF in a tensor form with the estimated errors, (6) slant-stacking with variable ray parameters, (7) estimating the travel times and amplitudes of the wave arrivals by Sompi Event Analysis (Hasada et al., 2001) and representing the result by a pulse sequence, and (8) deriving the polarization vector for each arrival to identify all the wave modes. We analyzed TF of SH-wave component from 16 to 20 Hz as an example. We obtained good quality TF with S/N ratio up to $10^4$ by stacking for 12 days at the step (3). The spatial noise originated from the local heterogeneity around the array was eliminated by the step (6). Several arrivals were recognized within the time windows from 0.6 to 1.8 s. The maximum amplitude of event traces was detected at the travel time of 1.064 s with a ray parameter of $7.9x10^{-4}$ s/m. We also found the scattered waves probably generated by the heterogeneities around the array. The ACROSS dense array observation would provide a lot of information on the underground heterogeneities. Consequently, we have the important and challenging subjects: (1) optimum designing of ACROSS array to acquire the better data and (2) development of new theoretical method to deal with the variable types of the wave.
DE: 7299 General or miscellaneous
DE: 7200 SEISMOLOGY
SC: Seismology [S]
MN: 2004 AGU Fall Meeting