A Stepwise Iterative Procedure to Constrain Stress Drop, Regional Attenuation Models, and Site Effects
Abstract
Accurate corrections for attenuation, geometrical spreading, source size, and site effects are needed for reliable use of regional seismic phases for discrimination and magnitude estimation Without constraints, the full parameter space has many trade-offs and instabilities that can lead to significant errors We are developing a stepwise iterative procedure, utilizing constraints, to provide more accurate parameter estimates. As a starting point, we use spectral ratios of regional phases for nearby events of different moments to eliminate path and site effects, yielding more reliable estimates of the source parameters. As shown by Schaff and Richards (2004) and Fisk et al. (2008), there are many pairs of nearby similar events throughout Eurasia available for this analysis. We then correct the spectra for source effects to be able to estimate more reliable distance and site corrections, adopting this same basic approach to constrain remaining tradeoffs. A key element of this effort is incorporation of coda envelope measurements, along with spectra of direct regional phases The stability of coda allows the analysis lobe applied to event pairs that are non-similar and may be separated by. e.g.. up to 50 km, greatly augmenting those that can provide accurate source terms. We have acquired from IRIS a very large dataset of three-component regional seismic recordings for events listed in the USGS PDE from 1989 to 2009 that have epicenter estimates within 50 km of another event, with at least 0.7 magnitude units difference, and the larger event of each pair at least mb 5. The set includes over 46,000 such pairs, corresponding to about 9,400 unique events. We have processed 599,226 waveforms to compute spectra of direct Pn. Pg, Sn, and/or Lg phases (of the order of 2,000.000 spectra) and coda envelopes in 16 frequency bands (about 10.000.000 envelopes). We have computed and fit a relative Brune (1970) source model to network median relative spectra for all 46,000 pairs.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 2010
- Accession Number
- ADA530812
Entities
People
- Mark D. Fisk
- W. S. Phillips