Regional Wave Attenuation and Seismic Moment from the Inversion of NORESS Spectra.
Abstract
Frequency-dependent regional wave attenuation along continental paths to the NORESS array in Norway is investigated. Regional Lg and Pn spectra from 190 events, at distances between 200 and 1300 km, have been inverted for seismic moment and apparent attenuation. Our method uses both the spectral and spatial decay of observed signal amplitudes to separate source ad path contributions. Based on adequate signal/noise, the Lg spectra were inverted between 1 and 7 Hz and the Pn spectra between 1 and 15 Hz. The data are parameterized by an omega - sq source spectrum with cube-root corner frequency scaling and an assumed geometric spreading function. Most events considered have local magnitudes less than 3.0, so the corner frequencies are near or beyond the upper limit of the bandwidth inverted. The spectra are inverted for source moment, a constant relating corner frequency and moment, and two parameters describing a power-law frequency dependence of Q. For fixed source and spreading assumptions, the inversion defines clear trade-offs among model parameters. To resolve these trade-offs, constraints are added to the separately derived source parameters Lg and Pn that they be consistent. The inversion results for seismic moment as a function of local magnitude are generally consistent with near-field studies. In that magnitude does not enter the inversion, this result lends considerable support to the derived Q models. The final result is an accurate parameterization of observed amplitude spectra of regional events recorded at NORESS that can be used to address a number of seismological problems related to wave propagation in the region and to the treaty monitoring capabilities of small regional networks.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jul 31, 1987
- Accession Number
- ADA187399
Entities
People
- Steven R. Bratt
- Thomas C. Bache
- Thomas J. Sereno Jr.
Organizations
- Leidos