HR: 0800h
AN: NS31B-0397    [Abstracts]
TI: Overview of a High Resolution VSP Survey in the International Continental Drilling Program Outokumpu Borehole, Finland: Progress Towards an Anisotropic Velocity Model
AU: * Schijns, H
AF: Inst. for Geophysical Research, Dept. of Physics, University of Alberta, Room #245 CEB 11322 - 89 Avenue, Edmonton, AB T6G 2G7, Canada
AU: Meillieux, D
AF: Inst. for Geophysical Research, Dept. of Physics, University of Alberta, Room #245 CEB 11322 - 89 Avenue, Edmonton, AB T6G 2G7, Canada
AU: Schmitt, D R
AF: Inst. for Geophysical Research, Dept. of Physics, University of Alberta, Room #245 CEB 11322 - 89 Avenue, Edmonton, AB T6G 2G7, Canada
AU: Kukkonen, I T
AF: Geological Survey of Finland, P.O. Box 96 (Betonimiehenkuja 4), Espoo, 02151, Finland
AU: Heikkinen, P
AF: Institute of Seismology, University of Helsinki, P.O. Box 68 (Gustaf Hällströmin katu 2b), Helsinki, 00014, Finland
AB: A high resolution borehole seismic survey was conducted in the ICDP Outokumpu, Finland scientific borehole to 1) assist in the interpretation of some earlier seismic profiles and 2) provide traveltime information that can be used to construct an anisotropic velocity model for use in future induced micro-seismic studies. The uppermost 1.3 km consists of a nearly flat-lying biotite schist expected to be highly intrinsically anisotropic; and the surveys further provide opportunity to study ansistropy from core to geological formation scales. The survey consisted of several parts, including a series of multi-azimuth multi-depth walk-away VSPs, a zero-offset VSP, and a surface seismic component. The zero-offset VSP was acquired at 2 m depth increments from 2500 m to 50 m, while the walk away VSPs were acquired with the receiver at the static depths of 1000 m, 1750 m and 2500 m. At the surface, the mica schist is overlain by a thin layer of glacial till. This stratification was confirmed by our VSP surveys. The effects of near surface heterogeneity were reduced using static corrections calculated from a velocity model developed using refraction tomography. The walk away seismic traces were then passed through a polarization filter and rotated into the direction of the P- and S-wave arrivals to increase the signal to noise ratio. Finally, a plane-wave decomposition technique was applied in order to determine the seismic velocity as a function of angle of incidence. Preliminary results from the 1000 m walk away VSP indicate that the P-wave velocity increases from 5250 m/s for vertical propagation to ~5620 m/s at 60° from vertical. Further work includes extending the anisotropy measurements to the 1750 m and 2500 m walk away, comparing the results to sonic logs, televiewer image logs, and laboratory anisotropy measurements on candidate core samples.
DE: 0902 Computational methods: seismic
DE: 0915 Downhole methods
DE: 7270 Tomography (6982, 8180)
SC: Near-Surface Geophysics [NS]
MN: 2007 Fall Meeting