3-D VISCOELASTIC ANISOTROPIC MODELING OF DATA FROM A MULTICOMPONENT, MULTIAZIMUTH SEISMIC EXPERIMENT IN NORTHEAST TEXAS

Three-component seismic data were acquired along six azimuths at a sit e in northeast Texas. Sources were inclined impacts combined to produc e equivalent vertical and crossline horizontal components. The data we re analyzed by iterative modeling using a new 3-D, staggered-grid, fin ite-differencing scheme. The 3-D model is defined in terms of spatiall y variable anisotropic, viscoelastic parameters (P-velocity, S-velocit y, density, Qp, and Qs) and converted to elastic tenser components and relaxation times for computation. Simultaneous fitting of amplitudes of near-surface reverberations, surface waves, converted waves, and de eper reflections gives an anisotropic, viscoelastic model that provide s constraints on earth properties. The assumption of transverse isotro py in previous experiments is supported by the results of this experim ent. 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 sha les are strongly transversely isotropic, with shear propagation veloci ty averaging 28% higher horizontally than vertically. The geometry of the Nacatoch Sandstone is similar, with approximate to 19% anisotropy. The marls and chalks are essentially isotropic. Observed mixing betwe en crossline and vertical components is incorporated by simulating a s mall (4 degrees) tilt of the axis of the impact source from vertical.