Robust Magnitude and Path Corrections for Regional Seismic Phases in Eurasia by Constrained Inversion and Enhanced Kriging Techniques
Abstract
This project is to develop and test two methods to improve magnitude and path corrections for regional seismic phase amplitudes. Objectives of the first method, a constrained inversion approach, are to improve estimates of geometrical spreading and Q for Pn, Pg, Sn, Lg in Eurasia, by eliminating trade-offs with source corner-frequency estimates, and to improve source parameterizations, in terms of grids of stress drop and corner frequency scaling. Using waveform cross-correlations from Dr. Schaff of Lamont-Doherty Earth Observatory for 4,236 events prior to 2000 in Eurasia, (1) data were obtained for event pairs or clusters in a data set from Los Alamos National Laboratory (LANL); (2) additional seismograms from IRIS were incorporated; (3) regional phase picks were added; (4) network-averaged relative spectra (for large-over-small event pairs) were processed for Pn, Pg, Sn and/or Lg; and (5) relative spectra of a Brune model were fit to the empirical relative spectra. Cases were considered with the apparent stress-drop scaling parameter, (as defined by Walter and Taylor, 2002), as a free parameter or fixed at 0.0 or 0.25. Preliminary kriged grids of stress drop have been computed for Eurasia, based on relative spectra for individual phases and combining the results for the various phases. The results thus far seem to show that the scaling of corner frequency with seismic moment for earthquakes is very consistent among the various regional phases. An interesting observation is that the estimated P- and S-wave corner frequencies for a given event are very similar for a majority of earthquake pairs throughout many diverse areas of Eurasia, comparable to findings by Walter and Taylor (2002) for western U.S. earthquakes. Important implications of this result are discussed. These analyses have been automated and are being applied to almost 3600 earthquake pairs in Eurasia from 2000 to 2007.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 2007
- Accession Number
- ADA519755
Entities
People
- Mark D. Fisk
- Steven R. Taylor