Computation of synthetic seismograms for stratified azimuthally anisotropic media
- Univ. of Hawaii, Honolulu (United States)
The authors outline a method of computing synthetic seismograms for stratified, azimuthally anisotropic, viscoelastic earth models. This method is an extended form of the Kennett algorithm that is efficient for multioffsett vertical seismic profiling. The model consists of a stack of homogeneous plane layers. In each layer, the 6 {times} 6 system matrix A is diagonalized numerically; this permits treatment of triclinic materials, i.e., those with the lowest possible symmetry. Jacobi iteration is an efficient way to diagonalize A because the entries of A change little from one wavenumber to the next. When the material properties are frequency dependent, the wavenumber loops are inside the frequency loop, and the computation is slow even on a supercomputer. When the material parameters are frequency independent, it is better to make frequency the deepest loop, with diagonalization of A outside the loop, in which case vectorization gives a relatively rapid computation. Temporal wraparound is avoided by making use of complex frequencies, and spatial aliasing is avoided by using a generalized Filon's method to evaluate both the wavenumber integrals. Various methods of generating anisotropic elastic constants from microlayers, cracks, and fractures and joints are discussed. Example computations are given for azimuthally isotropic and azimuthally anisotropic (AA) earth models. Comparison of computations using single and double wavenumber integrations for a realistic AA model shows that single wavenumber integration often gives incorrect answers especially at near offsets. Errors due to use of a single wavenumber integration are explained heuristically by use of wave front diagrams for point and line sources.
- OSTI ID:
- 5014576
- Journal Information:
- Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 95:B6; ISSN 0148-0227; ISSN JGREA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
580000* -- Geosciences
ALGORITHMS
ANISOTROPY
CALCULATION METHODS
COMPUTER CALCULATIONS
DATA ANALYSIS
ELASTICITY
ERRORS
FREQUENCY DEPENDENCE
GEOLOGIC FRACTURES
GEOLOGIC MODELS
GEOLOGIC STRATA
GEOLOGIC STRUCTURES
GEOPHYSICAL SURVEYS
MATHEMATICAL LOGIC
MEASURING INSTRUMENTS
MECHANICAL PROPERTIES
SEISMIC ARRAYS
SEISMIC DETECTORS
SEISMIC SURVEYS
SEISMOGRAPHS
SURVEYS
SYNTHESIS
TENSILE PROPERTIES
VISCOSITY