Generation of High Frequency P and S Wave Energy by Rock Fracture During a Buried Explosion: Its Effect on P/S Discriminants at Low Magnitudes
Abstract
High stresses in the source volume of an underground explosion produce a shell of crushed and fractured rock surrounding the shot point. We have modeled this process using a micro-mechanical damage mechanics in an effective medium source model to calculate the nucleation, growth, and interaction of fractures from an array of preexisting flaws. We have found that the nucleation and growth of fracture damage generates secondary seismic radiation that can be comparable in amplitude to the radiation generated by the pressure pulse itself. This secondary radiation is higher frequency than the primary radiation and can have a large shear wave component if there is a preferential orientation of the initial flaws or if there is a significant regional pre-stress field. It can be significant in the interpretation of regional discriminants that use local S phases. We have explored the scaling properties of this secondary radiation by modeling the chemical NPE explosion and US nuclear explosions in granite: HARDHAT, SHOAL, and PILEDRIVER. Finally, we have initiated work to understand the effect of frozen rock at the source point on the seismic coupling in hard rock. Existing data can be explained if ice controls the sliding friction on preexisting cracks.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 2004
- Accession Number
- ADA430614
Entities
People
- Charles G. Sammis
Organizations
- University of Southern California