Improved High Frequency Discrimination: A New Approach to Correct for Regional Source Scaling Variations (POSTPRINT) Annual Report 2

The Magnitude and Distance Amplitude Correction MDAC methodology of corrects ratios of regional phase amplitudes for source, path, and site effects and has proven effective for event identification. The MDAC formulation includes a term that describes the earthquake source scaling as the apparent stress variation with magnitude. In almost all regions there is evidence for non-self similar source scaling. The behavior of earthquake source scaling has been the topic of significant debate in the earthquake source community mainly because current methods require substantial path, site, and source radiation pattern corrections that ultimately yield large variance of the apparent stress. A new, state-of-the-art methodology, the coda ratio technique, provides unprecedented estimates for corner frequency and apparent stress drop, roughly 3 times less variance than conventional methods using a minimal number of stations and events. Within broad regions it is likely that apparent stress varies with location due to lateral variations in regional stress field, rheology, and degree of tectonic activity. Currently MDAC assumes a single linear apparent stress scaling with moment for a given region, but if there is a priori information on lateral variations in apparent stress, then this can be used to lower the amplitude ratio scatter and increase the discrimination capability. The coda ratio methodology has been applied to a variety of tectonic regions and clear distinctions between each of them have been found.