Abstract

A new short-period seismic magnitude measure based on uniform, automatic processing of digital P-wave data recorded on the standardized International Monitoring System (IMS) global network of stations has been formulated and tested. The test data consisted of over 220,000 single-station P-wave amplitude and period observations from approximately 25,000 events that were reported in the Reviewed Event Bulletin of the prototype International Data Center, which was established to evaluate various concepts proposed for use in the monitoring of nuclear explosions. Large-scale statistical analyses of these data have been used to define improved corrections for the effects of epicentral distance and focal depth, distance weighting factors for use in the estimation of a new, generalized mb measure (b) that incorporates data observed over the expanded epicentral distance range extending from 2° to 180°, as well as preliminary global station corrections for a number of existing and proposed IMS station sites. The station corrections are considered to be preliminary at this time since possible maximum-likelihood effects are not explicitly considered in the present analysis. However, evidence is presented that indicates that such effects are not significantly biasing the derived distance/depth corrections and that the magnitude of their influence on the estimated station corrections is likely to be rather small with respect to the range encompassed by these corrections. Tests of this new, generalized mb magnitude measure have indicated that it can provide consistent and easily reproducible measures of seismic event magnitude, even for events that are not well recorded at traditional teleseismic distances.

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