PNNL

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, there remain source effects such as those due to depth, focal mechanism, local material property and apparent stress variability that cannot easily be determined and applied as amplitude corrections. We develop a mathematical model to capture such effects as random (unknown) giving an error partition of two sources: model inadequacy and station noise. This mathematical model is the basis for a general multi-station regional discriminant formulation. The standard error of the discriminant includes the variances of model inadequacy and station noise in its formulation. The developed methods are demonstrated for a suite of Nevada Test Site (NTS) events observed at regional stations. Importantly, the proposed formulation includes all corrected amplitude information through the construction of multi-station discriminants. In contrast, previous studies have only computed discriminants from single stations having both P and S amplitudes. The proposed multi-station approach has similarities to the well established mb versus Ms discriminant.