Applications of a Next-Generation MDAC Discrimination Procedure Using Two-Dimensional Grids of Regional P/S Spectral Ratios
Abstract
Using extensions of theoretical source models for earthquakes and explosions, Fisk (2006, 2007) provided a consistent model-based explanation of the frequency dependence of regional P/S discriminants at all major nuclear test sites as mainly due to larger systematic differences in P- and S-wave corner frequencies for explosions than earthquakes, as well as different spectral shapes. This project focuses on exploiting this new understanding to improve discrimination of earthquakes and explosions using regional data. The main objective is to develop and test an innovative processing and discrimination procedure, based on robust features of multi-dimensional spectral ratios for regional seismic phases, and using comparisons to source models. In this paper, two-dimensional grids of P/S spectral ratios for all combinations of frequencies of P- and S-wave spectra are shown to exhibit much greater differences in relative spectral amplitudes and shapes between explosions and earthquakes than considered before. The approach builds naturally upon the Magnitude and Distance Amplitude Correction (MDAC) technique (Taylor and Hartse, 1998; Taylor et al., 2002; Walter and Taylor, 2002), correcting the spectra for source, geometrical spreading, attenuation, and site effects. The analysis is first applied to underground nuclear explosions (UNEs) at the Semipalatinsk Test Site and regional earthquakes recorded by station WMQ (Urumchi, China). Measurements from the grids are considered that include a traditional Pn/Lg discriminant, a broadband cross-spectral ratio (highfrequency Pn and low-frequency Lg), and the root-mean-squared misfit to the MDAC model, under the hypothesis of a Brune (1970) earthquake source. The latter two, especially cross-spectral Pn/Lg, are shown to vastly improve discrimination performance over traditional Pn/Lg and to increase the applicability rate due to higher Lg signal-tonoise at lower frequencies.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 2008
- Accession Number
- ADA516356
Entities
People
- Howard J. Patton
- Mark D. Fish
- Steven R. Taylor
- William R. Walter
Organizations
- Lawrence Livermore National Laboratory