Regional P-Coda for Stable Estimates of Body Wave Magnitude: Extending the M(s):m(b) Discriminant to Smaller Events

The most successful teleseismic discriminant is Msmb, and many studies are underway to try and 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 Msmb 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 mbs 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 Msmb discrimination, even though the mb estimates often had a large variance. The next obvious step to be implemented in the coda wave methodology is the use of P coda for mb estimates. This study focuses on developing a regional P-coda methodology to earthquakes and explosions on or near the Nevada, Shagan, Lop Nor, and Novaya Zemlya NZ test sites.