Regionalized Maximum Likelihood Surface Wave Analysis.
Abstract
We develop a method for regionalization of surface wave magnitudes, replacing the traditional Ms measurement with a new type of magnitude, the scalar moment, derived from the equations for surface waves from point sources in layered media. This has the effect of minimizing the frequency dependence and distance dependence of the magnitude, and allows worldwide regionalization so that the magnitude is a consistent measure of source size for any source and receiver location. Automatic surface wave processing has been implemented at the Prototype International Data Center since May, 1995, using a program, Maxsurf, developed by Maxwell Technologies. We have developed a new program Maxsurf, based on Maxsurf, with the addition of a phase-matched filtering module, and used it to estimate moments in automatic processing mode from a large data set of waveforms recorded at the GSETT 3 primary stations (3-Component long period and broadband stations and long period and broadband arrays). Regionalized earth models were developed on a 10 degree grid for phase velocity, group velocity, attenuation coefficients and surface wave source and path amplitude factors. The phase and group velocity models were refined using a tomographic inversion of group arrival time residuals from the large data set augmented by historical explosion data. The regionalized group velocity curves are used for identification of surface waves by comparing measured and predicted dispersion curves. The improved dispersion curves are a sufficiently good fit to the data over most of the world's surface to successfully compress waveforms using phase-matched filtering for an arbitrary path.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 1996
- Accession Number
- ADA321813
Entities
People
- J. L. Stevens
- K. L. Mclaughlin