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Accession Number ADA566744
Title Constraining Source Terms, Regional Attenuation Models, and Site Effects (Postprint).
Publication Date Mar 2012
Media Count 14p
Personal Author M. D. Fisk W. S. Phillips
Abstract This effort is directed at improving the calibration of Q, geometrical spreading, source, and site effects for regional seismic phases in Eurasia. As a starting point, spectral ratios of regional phases for nearby similar earthquakes of different moments have been used to eliminate path and site effects, giving more reliable estimates of source parameters. The spectra for the source terms are then corrected to estimate more reliable distance and site terms. There are many such pairs of events throughout Eurasia available for this Empirical Green's Function (EGF) analysis. In addition, a key element of this effort has been to incorporate coda envelope measurements in a suite of frequency bands. We compute a pseudo relative spectrum as the median ratio of coda envelopes in 16 frequency bands, which does not require the usual coda calibration. Coda is less sensitive to focal mechanism, event separation, and station coverage. Spectra of direct phases and coda envelopes each have distinct advantages; the independence of the methods and portions of the waveforms measured corroborates the estimated source terms or, in cases of discrepancies, helps identify problems. A large dataset of three-component regional seismograms from IRIS has been processed for events listed in the PDE from 1989 to 2009. A relative Brune (1970) source model has been processed and fit to network-median relative spectra for over 46,000 pairs, corresponding to about 9,400 unique events. Results with good corroboration of the moments and corner frequencies from coda and direct phases have been reviewed and selected. More recently, source-corrected spectra have been fit to estimate Q effects and the results compared to those of amplitude tomography work. These are orthogonal/independent approaches in the sense that the spectral fits estimate the frequency dependence of Q for fixed paths, while the tomography analysis estimates the path dependence of Q for 12 fixed frequency bands.
Keywords Eurasia
Greens functions
Seismic clusters
Seismic path effects
Seismic waves
Spectra
Symposia
Tomography


 
Source Agency Non Paid ADAS
NTIS Subject Category 48F - Geology & Geophysics
77D - Nuclear Explosions & Devices
Corporate Author Air Force Materiel Command, Wright-Patterson AFB, OH. Space Vehicles Directorate.
Document Type Technical report
Title Note Technical paper, 1 Sep 2010-21 Mar 2012.
NTIS Issue Number 1307
Contract Number FA8718-09-C-0005

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