HR: 0800h
AN: T51B-0551    [Abstracts]
TI: Seismic Constraints on the Deeper-water Transportation in the Mantle - Reflected Seismic Waves from the Slab-mantle Interface Revisited
AU: * Kawakatsu, H
EM: hitosi@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113- 0032, Japan
AU: Helffrich, G
EM: george@geology.bristol.ac.uk
AF: Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen's Road, BRISTOL, BS8 1RJ, United Kingdom
AU: Tonegawa, T
EM: tonegawa@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113- 0032, Japan
AB: Based on the analysis of seismic receiver functions, Kawakatsu and Watada (2007, Science) recently reported the presence of a low-velocity layer atop of the subducting slab beneath northeastern Japan, and interpreted it as a pathway of water transportation into the deep mantle down to a depth of ~150km. They also suggested that this low-velocity layer may continue to the deeper mantle in a cold subduction zone environment such as beneath the central/southwestern Japan, where various reflected and/or converted seismic waves from the deep slab-mantle interface have been reported. In order to give further constraints on the structure of the slab-mantle interface, the seismic reflection phase reported by Fukao et al. (1978, Nature), and later analyzed by Helffrich and Stein (1993, GJI) is revisited. We collected the dense network (J-array, Hi-net, F-net) recordings of earthquakes occurred in the Ryukyu arc. The preliminary analysis for events occurred in 2007 shows clear secondary arrivals which share similar characteristics (arrival times and slowness) with those of Fukao et al.'s observation. For example, the data of the 2007/4/20 19:37 event (h=48km, Mw 5.8) exhibit secondary arrivals in a distant range between 11.5 and 15.5 degrees with an apparent velocity of ~0.1degree/sec, some of which originate from reflections at the slab-mantle interface deeper than 200km. By analyzing earthquakes with various epicentral distances, the dense array recording of recent Japanese networks should allow us to obtain a tight constraint on the structure of the slab- mantle interface. A mineralogical model which is consistent with the seismic observation will be also attempted.
DE: 7240 Subduction zones (1207, 1219, 1240)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting