HR: 0800h
AN: S41A-0970    [Abstracts]
TI: Upper Mantle Heterogeneity Beneath the Siberian Craton From the PNE-Profile KIMBERLITE
AU: Pontevivo, A
EM: antonella@geol.ku.dk
AF: Geological Institute, University of Copenhagen, Oster Voldgade 10, Copenhagen, DK-1350 Denmark
AU: * Thybo, H
EM: thybo@geol.ku.dk
AF: Geological Institute, University of Copenhagen, Oster Voldgade 10, Copenhagen, DK-1350 Denmark
AB: We determine the physical properties of the seismic low-velocity layer (LVL) beneath the Siberian Craton at about 100 km depth in the upper mantle.
The profiles Kimberlite, Kraton and Meteorite were acquired with peaceful nuclear explosions (PNEs) as sources in the late `70s. The seismic sections of these three PNE-profiles clearly show a travel time delay at around 8 degrees offset that identifies the top of the LVL.
We perform 2D P-wave velocity modelling by application of seismic traveltime inversion along the high-resolution PNE seismic data profile Kimberlite, taking the Earth's sphericity into consideration. Reflections from discontinuities at average depths of 230, 300 and 410 km, refractions from the discontinuities at about 570 and 700 km depth, and travel time delays and scattered arrivals at ~700-1400 km offset interval have been identified. The 2D structure of this profile shows the presence of LVLs at average depths of 60-80 km and 110 km depth. The model is tested by the synthetic seismograms. A single-parameter uncertainty test for the most representative velocity and depth parameters of the model has been used for estimation of their absolute uncertainty. The two LVLs of our model lie within the depth range detected for the low-velocity zone by a seismological study with surface waves. The presence of the LVL below 100 km depth in cratonic areas has been demonstrated also from seismic tomographic inversion, full-waveform modelling, and petrological studies. The LVL lies within the depth range where a generalized shield geotherm is close to or above the solidus for mantle peridotite containing small amounts of C-H-O.
We will proceed with two-dimensional modeling and seismic traveltime inversion of the other two PNE profiles, Kraton and Meteorite. The comparison of the 2D structures of the three profiles will allow us to test for possible anisotropy in the LVL and to model the physical parameters of seismic scatterers in this layer.
DE: 0935 Seismic methods (3025, 7294)
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7218 Lithosphere (1236)
DE: 8103 Continental cratons
DE: 9320 Asia
SC: Seismology [S]
MN: Fall Meeting 2005