Wave Propagation from Complex 3D Sources Using the Representation Theorem
Abstract
In spite of extensive prior research on the generation of seismic waves by underground nuclear explosions, it is still not possible to provide a complete explanation for the observed wavefields, particularly at regional distances. Spherically symmetric explosion models embedded in layered elastic media effectively model the P phases generated by explosions and the major characteristics of some reflected and transmitted phases. Nonlinear axisymmetric finite difference calculations of explosions, including gravity and the effect of the free surface, can model a more realistic explosion source that directly generated shear waves. These models explain more characteristics of explosion-generated seismic waves, including some aspects of regional shear phases. However, it is clear that linear and nonlinear near-source 3D effects are important in many cases. SH waves are commonly observed within a few kilometers of explosions, too close to have been generated by (simple) conversion of vertical and radial components, and often larger than those components. Furthermore, it has not been established what impact 3D effects have on discriminants and on explosion yield estimates. It is important, therefore, to be able to model and understand how 3D source and source region heterogeneity affect the seismic wavefield and what impact this has on parameters used for nuclear monitoring. In this new project, we are implementing a technique that allows us to propagate the results of near-source 3D finite difference calculations to regional and teleseismic distances, and to use the results to investigate the impact of 3D near-source effects on regional and teleseismic phases, focusing in particular on the generation of SH phases by explosion sources. Our approach is to perform 3D explosion source region calculations, and then to propagate the wavefield to local, regional and teleseismic distances using layered earth Green's functions.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 30, 2008
- Accession Number
- ADA487585
Entities
People
- Heming Xu
- Jeffry L. Stevens
Organizations
- Leidos