HR: 0800h
AN: T21A-0359    [Abstracts]
TI: Precise relocations of deep low-frequency earthquakes beneath NE-Japan and estimation of 3-D seismic velocity structure in the surrounding areas
AU: * Nii, K
EM: nii@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, 6-6 Aza-Aoba, Aramaki, Aoba-ku, Sendai, 980-8578, Japan
AU: Okada, T
EM: okada@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, 6-6 Aza-Aoba, Aramaki, Aoba-ku, Sendai, 980-8578, Japan
AU: Ueki, S
EM: ueki@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, 6-6 Aza-Aoba, Aramaki, Aoba-ku, Sendai, 980-8578, Japan
AU: Nakajima, J
EM: nakajima@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, 6-6 Aza-Aoba, Aramaki, Aoba-ku, Sendai, 980-8578, Japan
AU: Zhao, D
EM: zhao@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, 6-6 Aza-Aoba, Aramaki, Aoba-ku, Sendai, 980-8578, Japan
AU: Hasegawa, A
EM: hasegawa@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, 6-6 Aza-Aoba, Aramaki, Aoba-ku, Sendai, 980-8578, Japan
AU: Zhang, H
EM: hjzhang@mit.edu
AF: Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139- 4307, United States
AU: Thurber, C H
EM: clifft@geology.wisc.edu
AF: Department of Geology and Geophysics, University of Wisconsin-Madison, 1215 West Dayton Street, Madison, WI 53706, United States
AB: It is well known that deep low-frequency earthquakes (DLFEs) with dominant frequency around 2 Hz occur at depths from 20 to 40 km in volcanic areas beneath NE-Japan (Hasegawa and Yamamoto, 1994; Okada et al., 2000). In addition, it has been pointed out that the source mechanism of DLFEs consists of both DC and non-DC components by moment tensor inversions (Okada et al., 2000; Nakamichi et al., 2003). These observations suggest that the generation mechanism of DLFEs is closely related with fluids (or magma). In this study, we precisely relocate the DLFEs occurring beneath Mt. Iwate and Mt. Naruko, determine the 3-D seismic velocity structure of the crust and uppermost mantle in the region surrounding them, and discuss the common characteristics for the two regions. We applied the DD tomography method (Zhang and Thurber, 2003) to data obtained by the seismic networks of Tohoku University, JMA and NIED. Note that we have included events within the subducting Pacific slab in the tomography inversion to increase the resolution of the lower crust structure. We employed the 3D seismic velocity model of the whole NE-Japan by Nakajima et al. (2001) as the initial model. Obtained results beneath Mt. Iwate show that DLFE forming two clusters are concentrated in the two locations to the south and the northeast of Mt. Iwate, respectively. Most of them are located at depths a few km shallower than the Moho and just above the low Vs and high Vp/Vs areas, which probably correspond to regions of partial melting. Note that they are located not within but above the S-wave low-velocity zone. This feature also can be seen for the DLFEs beneath Mt. Naruko.
DE: 6982 Tomography and imaging (7270, 8180)
DE: 7280 Volcano seismology (8419)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting