Seismic Anistropy and Large-Scale Porosity in the Ocean Floor
Abstract
Conventional marine seismic studies assume an isotropic velocity structure for marine sediments. Yet marine sediment cores routinely show anisotropy (Bachman 1979, 1983; Carlson, Schaftenaar & Moore 1984). Although highly anisotropic minerals such as calcite make up typical sediments, within each sedimentary microlayer these minerals orient randomly, making individual microlayers isotropic. Anisotropy of marine sediments results primarily from bedding, the interleaving of thin isotropic layers (Carlson et al. 1984). Any medium composed of different isotropic layers that are much thinner than a seismic wavelength is anisotropic. This lamellate medium will exhibit transverse isotropy with an axis of symmetry orthogonal to the layering (Postma 1955; Backus 1962). To completely describe the compressional and shear wave velocities of seismic waves travelling in an arbitrary direction through a transversely isotropic (TI) medium, five independent elastic parameters are required (Love 1920). Determining all five parameters necessitates recording compressional waves, and shear waves in two directions. Conventional marine seismic experiments may detect indications of anisotropy, such as mismatches between models derived from reflection and refraction studies (Davis & Clowes 1986) or discrepancies between seismic models and drill hole data (Banik 1984). But quantifying the anisotropy completely (i.e. determining all five parameters) is impossible unless unconverted shear waves are recorded. (eg)
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 31, 1989
- Accession Number
- ADA220453
Entities
People
- Gerard J. Fryer