Attenuation and Detection Capability of Regional Phases Recorded at NORESS
Abstract
The attenuation and detectability of regional Pn and Lg phases recorded at the NORESS array in Norway are estimated. We determine the frequency-dependent attenuation by inverting Pn and Lg single-channel spectra recorded at NORESS from 186 events at ranges between 200-1400 km with magnitudes between 1.1 and 4.8. The Pn spectra are inverted between 1-15 Hz and the Lg spectra between 1-7 Hz for both seismic moment and apparent attenuation. To resolve parameter trade-offs, we require that the separate Pn and Lg attenuation models produce an internally consistent set of source parameters. We find that regional Pn spectra are accurately described by 1/r to the 1.3 power geometric spreading and Q(f) = 325f to the 0.48 power. Lg spectra computed for a group velocity window of 3.6-3.0 km/s are consistent with cylindrical spreading and Q(f) = 560f to the 0.26 power. We determine the sensitivity of our estimates to the window length used in Fourier analysis, geometric spreading and source assumptions, and the inversion bandwidth. The final result is a simple parameterization of the source and range dependence of regional Pn and Lg spectra. Since signal detection is based on time domain amplitudes measured on filtered beams, a parameterization of single-channel spectra is not sufficient to determine detection capability, we determine a relationship between the spectral amplitudes used in the inversion and the time domain amplitudes used in signal detection.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 25, 1988
- Accession Number
- ADA196568
Entities
People
- Steven R. Bratt
- Thomas J. Sereno Jr.
Organizations
- Leidos