Numerical Experiments Investigating the Source of Explosion S-Waves
Abstract
In this study we use validated explosion simulations to investigate the locations at which explosion S-waves originate. Several mechanisms for generating S-waves from an explosion source have been put forward. These mechanisms include tectonic release, non-symmetrical source effects, non-linear source effects, conversion of P-waves to S-waves off the free surface, and scattering of near-source Rayleigh waves. Each of these mechanisms is physically sound, and each mechanism likely contributes to the observed S-wave field. Identifying where explosion S-waves originate provides an important constraint on the contribution of each S-wave mechanism. The simulations in this study are based on the well-recorded 1993 Nonproliferation experiment (NPE) (chemical kiloton). A regional 3-dimensional model surrounding the NPE is validated by first extracting vertical cross-sections cutting through the NPE source and stations at which the NPE was recorded. We then generate synthetic seismograms using a 2-dimensional finite difference calculation for each event-station path. Good agreement between synthetic and observed seismograms provides confidence that the model and simulations are reasonably accurate. The origin of S-waves is determined through both analysis of the simulated wavefield evolution and using the timereversal method to refocus far-field S-waves back to their origin. Preliminary results suggest that the primary S-wave pulse originates near the free surface and at high-impedance geologic interfaces that are close to the explosion. These results suggest that scattering can account for much of the observed S-wave energy radiated from the NPE explosion.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 2007
- Accession Number
- ADA518877
Entities
People
- Jeffrey L. Wagoner
- Shawn C. Larsen
- Stephen C. Myers
Organizations
- Lawrence Livermore National Laboratory