HR: 0800h
AN: S51E-1055    [Abstracts]
TI: Depth Extent of Continents: A New Look Based on Shear-Wave Velocity Models Inferred From Higher Modes of Rayleigh Wave Observed Across California and the Kaapvaal Craton Seismic Networks
AU: Merrer, S
EM: sophie.merrer@laposte.net
AF: EOST, IPGS 5 rue R. Descartes, Strasbourg, f67084 France
AU: * Cara, M
EM: Michel.Cara@eost.u-strasbg.fr
AF: EOST, IPGS 5 rue R. Descartes, Strasbourg, f67084 France
AU: Rivera, L
EM: Luis.Rivera@eost.u-strasbg.fr
AF: EOST, IPGS 5 rue R. Descartes, Strasbourg, f67084 France
AU: Ritsema, J
EM: j.ritsema@gmail.com
AF: University of Michigan, Department of Geological Sciences, Ann Arbor, MI MI48710 United States
AB: Seismic structure of the upper mantle is best constrained with wavespeed measurements of overtone Rayleigh waves in the period range 30-100 seconds. However, it is difficult to make these measurements because the various overtone Rayleigh waves interfere. Wavenumber modelling is an effective way to isolate overtone branches, especially using seismograms from a long (> 1000 km) array of stations. It has been applied long time ago to WWSSN stations (Nolet, 1975; Cara, 1977). Thanks to the deployment of dense arrays of broad-band stations, we now can apply such techniques to records of much better quality. Two sets of seismograms recorded in California (TriNet+BDSN) and Baja-California (NARS-Baja) and in South Africa (Passcal-SASEK-Kaapvaal) have been analysed to infer the shear-wave velocity structure of the upper mantle beneath two drastically different tectonic provinces: Western North America, from northern California to the southern Baja California, and the Kaapvaal craton. We have compared our overtone phase velocity measurements to predictions using a homogeneous pyrolitic upper mantle structure with different potential temperatures. The upper-mantle shear-wave velocity beneath California is compatible with our overtone observations for the highest temperature adiabat we have tested, i.e. 1500°C. Although of poorer quality, the Kaapvaal phase-velocity data, does not support the presence of a deep continental root beneath the Kaapvaal craton. At the upper-mantle transition region depths (400-600 km) our inverted models show an intriguing feature: while the California model remains very close to the global shear-wave velocity values, the Kaapvaal craton exhibits a positive anomaly around 0.1 km/s which is necessary to explain the high - although quite scattered - phase velocities of the second, third and fourth overtone.
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7255 Surface waves and free oscillations
DE: 7270 Tomography (6982, 8180)
DE: 9305 Africa
DE: 9350 North America
SC: Seismology [S]
MN: Fall Meeting 2005