HR: 0830h
AN: S11C-0294    [PDF]
TI: P-wave Velocity Anisotropy and Shear-wave Splitting of Sheared Metasediments from the Flin-Flon Belt, Trans-Hudson Orogen
AU: Schmitt, D R
EM: doug@phys.ualberta.ca
AF: Institute for Geophysical Research, Department of Physics, University of Alberta, Edmonton, AB T6E 2J1 Canada
AU: * Cholach, P Y
EM: pcholach@phys.ualberta.ca
AF: Institute for Geophysical Research, Department of Physics, University of Alberta, Edmonton, AB T6E 2J1 Canada
AU: Molyneux, J B
EM: joe.b.molyneux@exxonmobil.com
AF: Institute for Geophysical Research, Department of Physics, University of Alberta, Edmonton, AB T6E 2J1 Canada
AU: Molyneux, J B
EM: joe.b.molyneux@exxonmobil.com
AF: ExxonMobil, 222 Benmar, P.O. Box 4778, Houston, TX 77210-4778 United States
AB: Metasediments of the upper greenschist - lower amphibolite facies of metamorphism from two ductile shear zones of Flin-Flon Belt (FFB) of Trans-Hudson Orogen (THO) were used to carried out laboratory measurements of compressional wave (Vp), shear-wave (Vs) velocities and shear-wave splitting. The investigated metasediments vary in composition from felsic to mafic. Test sites with outcrops of sheared metasediments were correlated with a series of inclined seismic reflectors possibly extending from the midcrust and intersecting a well mapped shear zone at the surface. Determination of lithological and physical properties of highly deformed metasediments is essential for proper interpretation of the nature of observed seismic reflectors. To investigate anisotropic properties of the rocks compressional velocity was measured to confining pressures of 300 MPa in three mutually orthogonal directions with respect to the visible textural properties. In addition, on nine selected samples shear-wave velocity was measured at two orthogonal polarizations for each of three propagation directions to determine shear-wave splitting and correlate it with P-wave anisotropy. For most of the hand specimens seismic heterogeneity was investigated by measuring P- and S-wave velocities on several cores cut in the same direction. Elastic velocities were measured on the 147 core samples in total. Observed Vp anisotropy varied from quasi-isotropic to highly anisotropic (Ap=24%). Maximum observed shear wave splitting reaches the value of 0.77 km/sec at confining pressure of 300 MPa. An estimated splitting of the SKS wave propagating through the ten kilometres thick crustal slab of metasediments, characterized by the averaged value of laboratory observed shear-wave splitting, may reach value of 0.2 sec. Pressure invariance of observed P-wave anisotropy and shear-wave splitting indicates that lattice preferred orientation (LPO) of highly anisotropic minerals such as mica and hornblende is mainly responsible for measured seismic anisotropy.
DE: 3909 Elasticity and anelasticity
DE: 5102 Acoustic properties
DE: 7218 Lithosphere and upper mantle
DE: 7260 Theory and modeling
SC: Seismology [S]
MN: 2003 Fall Meeting