Explosion Source Models for Seismic Monitoring at High Frequencies: Quantification of the Damage Source and Further Validation of Models
LOS ALAMOS NATIONAL LAB NM
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This paper reports on the first years accomplishments of a new project to extend explosion models, accounting for source medium damage, to high frequencies. This project builds on a previous three-year project which developed kinematic source descriptions for such models and investigated the seismic radiation for frequencies below 0.2 Hz. Direct and indirect effects of shock waves including free surface interactions cause material damage which in general contributes volumetric, compensated linear vector dipole CLVD, and double-couple DC sources of seismic radiation. The past project studied two important features of these models i Rayleigh waves excited by a CLVD source and the impact on performance of mb-Ms discrimination and ii volumetric moment caused by damage and its impact on estimates of isotropic moment MI and yield estimation. The goal of the current project is to advance these models with a sound physical basis in order to study S wave generation for high frequencies. The tasking is broken down into three major phases 1 develop and quantify mathematical descriptions of effective source functions for damage, which, up until now, were assumed to be a step function, 2 test and validate models against observed spectral features of PS ratios for the 0.5-3 Hz band, and 3 test and validate models against scaling observations of PS ratios for the 1-10 Hz band. This years work involved empirical studies quantifying the amount of volumetric moment contributed by source medium damage.