Applications of a Constrained Inversion and an Extended Kriging Method to Improve Source, Path, and Site Corrections for Regional Seismic Phases
Abstract
Objectives are to develop and apply two methods to improve source and path corrections for regional seismic phases. In first, we estimate and constrain source parameters using Brune model fits to relative spectra of regional seismic phases for event pairs with similar locations and focal mechanisms, but different seismic moments. We then use source-corrected spectra to estimate geometrical spreading, Q, and site terms for Pn, Pg, Sn, and Lg. We performed preliminary study using waveform cross-correlations to find suitable pairs. Using Preliminary Determination of Epicenters catalog, we formed a list of candidate pairs and computed waveform cross-correlations to find pairs of similar events. We computed and fit network-median relative spectra for 3,600 pairs. We automated processing steps, reviewing and refining results. We merged results with previous to obtain more extensive estimates of source corner frequencies versus moment and stress-drop parameters. We generated kriged grids of stress drop and associated uncertainties. We fit combined distance and site terms to the source-corrected spectra, showing robust estimates of these effects are possible by first constraining source terms. Second method, an extension to Bayesian kriging, provides robust path corrections and uncertainties for regional phase amplitudes, that properly treats localized calibration events that may have anomalous, correlated amplitudes. Clusters of anomalous reference events can significantly bias kriged amplitude corrections and uncertainties. Fisk and McCartor developed a fundamental improvement to kriging methodology, incorporating an additional correlation length to treat similar focal mechanisms, and tested the method on large samples of underground nuclear explosions and earthquakes. Application to worldwide datasets indicates power of hypothesis test to reject earthquakes as explosions is marginally reduced, without miscategorizing known explosions and providing robust treatment of clu
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 2008
- Accession Number
- ADA518299
Entities
People
- Mark D. Fisk
- Steven R. Taylor