Regional P-Coda for Stable Estimates of Body Wave Magnitude: Application to Novaya Zemlya and Nevada Test Site Events

Abstract

Abstract : Regional seismic explosion monitoring requires the discrimination of small clandestine nuclear explosions from background earthquakes. most successful teleseismic discriminant, the so-called Ms:mb, discriminant, compares the long-period surface waves magnitude (Ms) with the period P-based body wave magnitude (mb). There are many studies underway to try and extend surface wave magnitude (Ms) estimation to re distances and smaller magnitudes. Another problem that is encountered is how to estimate mb so that the Ms:mb discriminant is meaningful a consistent with teleseismic measures. For small-to-moderate sized events, the teleseismic body wave magnitude, mb(P), cannot be effectively measured due to low signal-to-noise ratio. We develop a stable regional alternative based on the P-coda that scales 1-to-1 with the teleseismic mb(P), but with the advantage of lower variance. Though mb(Lg) and mb(Lg-coda) can be tied to mb(P) for explosions, they overpredict earth magnitudes by ~0.5-1 magnitude units and degrade the performance of the Ms:mb discriminant. In contrast, mb(P-coda) does not exhibit this and can be used to extend Ms:mb to smaller regional events.