Seismic monitoring for underground nuclear explosions answers three questions for all global seismic activity: Where is the seismic event located? What is the event source type (event identification)? If the event is an explosion, what is the yield? The answers to these questions involves processing seismometer waveforms with propagation paths predominately in the mantle. Four discriminants commonly used to identify teleseismic events are depth from travel time, presence of long-period surface energy (m b vs. M S ), depth from reflective phases, and polarity of first motion. The seismic theory for these discriminants is well established in the literature (see, for example, Blandford [1982] and Pomeroy et al. [1982]). However, the physical basis of each has not been formally integrated into probability models to account for statistical error and provide discriminant calculations appropriate, in general, for multidimensional event identification. This article develops a mathematical statistics formulation of these discriminants and offers a novel approach to multidimensional discrimination that is readily extensible to other discriminants. For each discriminant a probability model is formulated under a general null hypothesis of H 0 : Explosion Characteristics. The veracity of the hypothesized model is measured with a p-value calculation (see Freedman et al. [1991] and Stuart et al. [1994]) that can be filtered to be approximately normally distributed and is in the range [0, 1]. A value near zero rejects H 0 and a moderate to large value indicates consistency with H 0 . The hypothesis test formulation ensures that seismic phenomenology is tied to the interpretation of the p-value. These p-values are then embedded into a multidiscriminant algorithm that is developed from regularized discrimination methods proposed by DiPillo (1976), Smidt andMcDonald (1976), andFriedman (1989). Performance of the methods is demonstrated with 102 teleseismic events with magnitudes (m b ) ranging from 5 to 6.5. Example p-value calculations are given for two of these events.

No abstract

No abstract

To effectively monitor a Comprehensive Test Ban Treaty, seismologists must be able to confidently detect and identify low-yield explosions. This requires the use of short-period regional phases, which can be extremely complicated. The Non-Proliferation Experiment (NPE) was a low-yield chemical explosion detonated at the Nevada Test Site (NTS) and recorded at more than 50 broadband seismic stations located throughout the western United States. These data were used to investigate the development of Lg and Pn, two seismic phases used in regional discriminants. The frequency-dependent attenuation for Lg recorded at 43 stations is described by the relation QLg (vertical) = 238 f1.28. The amplitude decay for Pn recorded at 38 stations is proportional to Δ−(1.29 + 0.05f) for the frequency window of 1 to 6 Hz. After removing the effects of distance and attenuation, we found the values of the spectral ratio Lg (4-6)/(2-4) to group according to the geologic terrain associated with the path traveled. Stations located within the Basin and Range had lower ratio values than stations located outside the Basin and Range. However, for the spectral ratio Pn (2-4)/(4-6), geologic terrain had an indirect effect. Pn is affected by Moho structure associated with the backazimuth, causing an azimuthal dependence. Of course, Moho structure can be a function of geologic terrain. Furthermore, the Pn arrival may be large or small, independent of azimuth. The values of the discriminant phase ratio Pn (1-2)/Lg (2-4) have an order of magnitude more scatter than Lg/Lg or Pn/Pn. Nonetheless, the values are both a function of geologic terrain (the Lg contribution) as well as Moho structure (Pn contribution).