HR: 1340h
AN: S13B-1044    [Abstracts]
TI: Transition zone structure of California from Ps converted waves
AU: * Cupillard, P
EM: paulcup@ipgp.jussieu.fr
AF: IPG Paris, Tour 24-14 4, place Jussieu, Paris, 75252 France
AU: Ritsema, J
EM: jeroen@ipgp.jussieu.fr
AF: IPG Paris, Tour 24-14 4, place Jussieu, Paris, 75252 France
AB: We present new estimates of the structure of seismic discontinuities in the upper mantle of California and the northern Gulf of California from the analysis of stacks of 10,000 TriNet, Berkeley Digital Seismic Network, and NARS-Baja waveforms. Throughout the region, Ps conversions from the 410-km and 660-km conversions arrive 2-3 s later than predicted by IASP91, due to low seismic velocities in the uppermost mantle of western North America. In addition, the differential traveltime of P660s and P410s is up to 1 s shorter than predicted by IASP91, which is among the lowest values observed worldwide, in accord with earlier observations of single-station stacks. This suggests that the transition zone beneath California is as thin as beneath various hotspot regions, and that the temperature of the mantle beneath California is elevated to at least 400 km depth. We will evaluate whether our observations can be reconciled with models of the upper mantle that invoke variations of shear and compressional velocity due to temperature alone.
DE: 7299 General or miscellaneous
SC: Seismology [S]
MN: 2004 AGU Fall Meeting