A Stepwise, Iterative Procedure to Constrain Stress Drop, Regional Attenuation Models, and Site Effects
Abstract
Accurate corrections for distance, source size, and site effects are needed for reliable use of regional seismic phases for discrimination and magnitude estimation. Procedures that simultaneously invert for attenuation, geometrical spreading, site, and source parameters have been shown to include many trade-offs and instabilities that have led to significantly inaccurate corrections for distance and source terms. Under previous work, we developed and applied an approach to constrain source parameters, including stress drop, for events throughout Eurasia, using Brune (1970) model fits to relative spectra of regional phases for event pairs with similar locations and mechanisms (assessed by waveform correlations), but different moments. We further fit the combined distance and site terms to the source-corrected spectra, showing that robust estimates of these combined effects are possible by first constraining source terms. Further work is needed to separately constrain the path and site effects. We have just started a three-year project to implement, apply, and evaluate a stepwise, iterative procedure to constrain all of the remaining trade-offs among these terms. Using spectra of regional seismic phases that are already corrected for source terms, we will estimate and apply corrections for frequency-independent geometrical spreading and site factors, based on distance, and then constrain separate estimates of frequency-dependent site parameters and Q. This is expected to provide accurate estimates of all source, distance, and site effects for regional phases in Eurasia for paths/stations with suitable data. We also plan to use coda measurements and methods to (1) augment our source terms computed from spectra of direct phases, (2) independently estimate site terms, and (3) compare and validate the results using direct phases or coda.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 30, 2009
- Accession Number
- ADA505383
Entities
People
- Mark D. Fisk
- W. S. Phillips