A Unified Direct-Plus-Coda Amplitude Model for Explosion Monitoring

Session: Explosion Seismology Advances [Poster]
Type: Poster
Date: 4/29/2020
Time: 08:00 AM
Room: Ballroom
Description: 

We exploit high frequency, local and regional phases and their codas for event discrimination and yield estimation research. The close-in data enable study of small explosions and the stability of coda waves allows us to obtain high precision with as few as a single recording station. In monitoring scenarios, the stability of the coda is the result of the redundancy of the measurement, but not the path averaging nature of the scattered waves. We must use short coda closely following the direct waves, rather than the Rautian-Khalturin standard of beginning at twice the arrival time that ensures path averaging. Thus, both coda and direct phases show similar path or attenuation behavior with distance. We have shown that 2-D maps of coda and direct phase attenuation follow regional geology spectacularly well and applying subsequent path corrections improves discrimination power and yield estimation accuracy. To this point, however, direct and coda models have been independent of each other, as they were inverted for separately. These inversions solve for source, path and site effects, which means the two models obtain different source spectra for the same events. We rectify this by solving for direct and coda models simultaneously, thus enforcing the same source spectra for all phase types, while still allowing attenuation and site terms to vary independently. We use standard direct phase spreading models for Pn, Pg, Sn and Lg, as well as improved models for the Pn phase derived by Yang. Local S and Lg coda spreading models start out flat at zero distance, consistent with the distance independence observed by Aki for local coda, but evolve to the direct wave spreading behavior with distance. Pn, Pg and Sn coda spreading are fixed to the direct wave models, as their codas are normally very short. We will show unified model results, including evidence for the high stability of coda of all phases and application to studies of monitoring interest.

Presenting Author: William S. Phillips

Authors