Regional P Coda for Stable Estimates of Body Wave Magnitude: Extending the Ms:mb Discriminant to Smaller Events
Abstract
The most successful teleseismic discriminant is Ms:mb, and many studies are underway to try to extend surface wave magnitude (Ms) estimation to regional distances. A problem that is encountered at regional distances and small magnitudes is how to estimate mb so that the Ms:mb discriminant is meaningful and consistent with teleseismic measures. Over the past several years, a regional S-coda wave methodology has been developed that provides for the lowest variance estimate of the seismic source spectrum. Thus, regional MW and mb estimates derived from Sn and Lg coda are very stable, even when only a single station is used. However, these mb's are inherently biased for earthquakes because they are an S-based measurement, and explosions are relatively depleted in S-waves. Previous research projects have used region-specific mb scales based on direct measurements of Pn and Pg to improve the Ms:mb discrimination, even though the mb estimates often had a large variance. In our preliminary research, we have found that P-coda envelopes for both explosions and earthquakes can be obtained for events from both the Nevada Test Site (NTS) and Novaya Zemlya (NZ) regions without bias. Our next step at NTS will be to derive path corrections, similar to the approach of Mayeda et al. (2003) for Lg-coda. We will compare inter-station scatter of distance-corrected amplitudes as a function of window length. This will provide an empirical measure of error based on window length for each frequency band. For each frequency band, we will regress our coda envelope amplitudes against regional and teleseismic estimates of mb (e.g., mb(Pn), mb(P)) to determine which band provides the lowest variance. This will yield slope and intercept values for each frequency band. We will then derive mb(Pn) and mb(P) (following Denny et al., 1989) to compare against mb(P-coda) to assess performance at the network and single-station level.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 2007
- Accession Number
- ADA519372
Entities
People
- Jessie Bonner
- Kevin Mayeda