HR: 1340h
AN: S43B-0996    [Abstracts]
TI: A synthesis on lower mantle reflectors/scatterers and discontinuities beneath the western Pacific subduction zones
AU: * Vanacore, E
EM: evanacor@rice.edu
AF: Department of Earth Science, Rice University, 6100 Main St, Houston, TX 77005 United States
AU: Niu, F
EM: niu@rice.edu
AF: Department of Earth Science, Rice University, 6100 Main St, Houston, TX 77005 United States
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 Japan
AB: Strong seismic reflectors/scatterers and discontinuities have been observed in the lower mantle at various depths beneath western Pacific subduction zones. The lateral extension of these anomalous structures, however, is not well constrained. The information may hold the key to the understanding of the nature of these seismic structures as well as the related mantle processes. For example, are these seismic anomalies primordial chemical reservoirs, or pieces of subducted oceanic crusts or even parts of a highly heterogeneous global compositional boundary? In this study, we used teleseismic S to P and P to S converted waves to determine the locations and depths of lower reflectors/scatterers and discontinuities in the western Pacific. Our data are collected from several seismic arrays (J-array and Hinet in Japan, the Kaapvaal broadband seismic array, and short-period arrays in the western US) from recent deep earthquakes occurred in the study regions. The spread of conversion points among various arrays allow us to better constrain the lateral extension of the anomalous structure. For example, the mid-mantle discontinuity observed by {\it Niu and Kawakatsu} [1997] at the 110$\deg$E, 5$\deg$S appears to extend to further south and west by at least 100 km once the Kaapvaal data is combined. For the islands in the study region where seismic arrays are available, for example Japan and Indonesia, we also conduct receiver-function imaging to improve geographic coverage. By combining different types of seismic data, we expect to achieve a synthesized view of anomalous structures at middle to lower mantle depths.
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 7203 Body wave propagation
DE: 7207 Core and mantle
SC: Seismology [S]
MN: 2004 AGU Fall Meeting