Effects of a Descending Lithospheric Slab on Yield Estimates of Underground Nuclear Tests
Abstract
A method for computing seismic wavefields in a high frequency approximation is proposed based on the integration of the kinematic ray tracing equations and a new set of differential equations for the dynamic properties of the wavefront, which we call the vicinity ray tracing equations. These equations are directly obtained from the Hamiltonian of a ray in ray centered coordinates, using no paraxial approximations. This system is comparable to the standard dynamic ray tracing system, but it is specified by fewer equations (4 versus 8 in three-dimensions) and only requires the specification of velocity and its first spatial derivative along a ray. The vicinity ray tracing equations define the locus of a ray in the neighborhood of the central ray. The path of the vicinity ray is predicted using properties of the medium along the vicinity ray rather than properties of the medium along the central ray. Gaussian beams are defined by assigning a Gaussian distribution of amplitude to each central ray. The width of the Gaussian is taken to be the Fresnol volume surrounding the central ray, estimated from the frequency and the distance of the vicinity ray from the central ray. Because no paraxial approximations are made, the superposition of the Gaussian beam defined from vicinity rays will exhibit a much slower breakdown in accuracy as the scale length of the medium given by v/ Delta v approaches the beamwidth. Since second spatial derivatives of velocity are not required by the new technique, parameterization of the medium is simplified, and reflection and transmission of beams can be calculated by applying Snell's law to both vicinity rays and central rays.
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 28, 1989
- Accession Number
- ADA213305
Entities
People
- Vernon F. Cormier
- Woohan Kim
Organizations
- University of Connecticut