Explosion Source Models for Seismic Monitoring at High Frequencies: Quantification of the Damage Source and Further Validation of Models.

摘要

This paper reports on the first year's 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 approximately 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 P/S ratios for the 0.5-3 Hz band, and (3) test and validate models against scaling observations of P/S ratios for the 1-10 Hz band. This year's work involved empirical studies quantifying the amount of volumetric moment contributed by source medium damage.