Regional Multistation Discriminants: Magnitude, Distance, and Amplitude Corrections, and Sources of Error

Abstract

Magnitude, distance, and amplitude corrections (MDAC) made to observed regional amplitudes are necessary so that what remains in the corrected amplitude is mostly information about the seismic source type. Corrected amplitudes can be used in ratios to discriminate between earthquakes and explosions. However, source effects remain that cannot easily be determined and applied as amplitude corrections, such as those due to depth, focal mechanism, local material property, and apparent stress variability. We develop a mathematical model to capture these nearsource effects as random (unknown), giving an error partition of three sources: model inadequacy, station noise, and amplitude correlation. This mathematical model is the basis for a general multistation regional discriminant formulation. The standard error of the discriminant includes the variances of model inadequacy and station noise, along with amplitude correlation in its formulation. The developed methods are demonstrated for a collection of Nevada test site (NTS) events observed at regional stations (see Fig. 1). Importantly, the proposed formulation includes all corrected amplitude information through the construction of multistation discriminants. In contrast, previous studies have only computed discriminants from single stations having both P and S amplitudes. The proposed multistation approach has similarities to the wellestablished m b versus M s discriminant and represents a new paradigm for the regional discrimination problem.

Seismic event identification

“…(7), the standard error of the m b versus M S discriminant is for both earthquakes and explosions and the test statistic is providing a P ‐value for the hypothesis test H 0 : m̃ b − M̃ S ≥ Δ 0 . We note that this extended formulation of the m b versus M S discriminant is analogous to the formulation of regional amplitude discriminants in Ref 8 and reviewed below.…”

“…This article presents the construction of teleseismic and regional (seismic waves with crustal paths) discriminants and two additional multi‐technology discriminants derived from infrasonic wave measurements. Coupled with researched sources‐of‐error models for each discriminant, a general strategy for the construction of diverse multi‐technology discriminants has been developed in Refs 7 and 8. This article reviews these developments, including some new extensions, and demonstrates each with open data.…”

“…The difference of regional P (e.g., P n or P g ) and S (e.g., S n or L g ) wave amplitudes at high frequencies can discriminate between earthquakes and explosions (see Refs 36–38). The sources‐of‐error model for regional phase amplitude discriminants is developed in Ref 8. Specifically, for P g versus L g , both constructed with a 6–8 Hz filter window, the competing hypotheses are H 0 : µ − µ ≥ Δ 0 and H A : µ − µ < Δ 0 .…”

NetCAP status report for the end of fiscal year 2010.

“…Network based discriminants follow the framework designed for use with MDAC calibrations (Anderson et al, 2009) for regional phase discrimination that fully attributes residuals between observations and predictions to two normally distributed error event and station terms and a bias due to source type. Variances from the error terms are used in the discriminant calculations, but also can be used to provide populations that can be sampled.…”

Joining statistics and geophysics for assessment and uncertainty quantification of three‐dimensional seismic Earth models

“…IDC's responsibility includes the release of bulletins that report on locations and analyses of seismic events. These analyses assess whether or not the event has nuclear explosion characteristics (eg [3,30]) and depend on the seismic models they use. The accuracy on seismic event location is critical to any onsite inspection (OSI) should sufficient IDC technical evidence warrant an OSI.…”