HR: 0800h
AN: S41C-1009    [Abstracts]
TI: Search for mid-mantle discontinuities at approximately 1000 km depth in South America using S to P conversions and SS precursors
AU: * Vanacore, E A
EM: evanacor@rice.edu
AF: Rice University Dept of Earth Science, 6100 Main St, Houston, TX 77005
AU: Niu, F
EM: niu@rice.edu
AF: Rice University Dept of Earth Science, 6100 Main St, Houston, TX 77005
AB: Mid-mantle discontinuities associated with tomographic high velocity anomalies (HVA) have been previously observed using S to P conversions and SS Precursors in the West Pacific. In this study the authors investigate the HVA beneath South America in the region between 0° and -28° latitude and -80° and -55° longitude. Data from the Southern California Seismic Network and a temporary PASSCAL network in South Africa (1997-1999) for events at greater than 300 km depth in the region occurring between 1994 and 2004 are analyzed using a 4th root stacking method with respect to the P wave arrival. Data from the SCSN sample the edge of the regional HVA; preliminary results from these events have been inconsistent with depths ranging from approximately 800 km to 1200 km when observed in the data. The inconsistency of the data is likely due to the sampling issue mentioned above; the Kapavaal data provides a preferable geometry and sampling of the HVA. Analysis of this data will provide better insight into the existence and geometric character of discontinuities/reflectors in the South American HVA. Global SS Precursor data is analyzed for the region applying a 4th root stacking method in order to examine energy reflected at depth from the underside of any discontinuities/reflectors in the region. The SS precursor data is sub-divided into regions based upon the presence of the HVA as defined by regional tomography from Grand et al (1997) before stacking. Analysis of SS Precursors in the HVA reveals energy at approximately 1200 km depth; analysis of SS precursor data outside of the HVA reveals energy at approximately 820 km depth but lacks energy at greater depths.
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7240 Subduction zones (1207, 1219, 1240)
SC: Seismology [S]
MN: Fall Meeting 2005