3-D viscoelastic anisotropic modeling of data from a multicomponent, multiazimuth seismic experiment in northeast Texas

摘要

Three-component seismic data were acquired along six azimuths at a site in northeast Texas. Sources were inclined impacts combined to produce equivalent vertical and crossline horizontal components. The data were analyzed by iterative modeling using a new 3-D, staggered-grid, finite-differencing scheme. The 3-D model is defined in terms of spatially variable anisotropic, viscoelastic parameters (P-velocity, S-veloc-ity, density, Qp, and Qs) and converted to elastic tensor components and relaxation times for computation. Simultaneous fitting of amplitudes of near-surface reverberations, surface waves, converted waves, and deeper reflections gives an anisotropic, viscoelas- tic model that provides constraints on earth properties. The assumption of transverse isotropy in previous experiments is supported by the results of this experiment. The final model consists of a stack of flat layers, each of which has isotropic P-velocity, Qp, and Qs. The Wills Point and Kincaid shales are strongly transversely isotropic, with shear propagation velocity averaging 28% higher horizontally than vertically. The geometry of the Nacatoch Sandstone is similar, with ≈19% anisotropy. The marls and chalks are essentially isotropic. Observed mixing between crossline and vertical components is incorporated by simulating a small (4°) tilt of the axis of the impact source from vertical.