Attenuation Tomography of Northern California and the Yellow Sea/Korean Peninsula from Coda-Source Normalized and Direct LG Amplitudes
Abstract
Inversions for regional attenuation (1/Q) of Lg are performed in two different regions. The path attenuation component of the Lg spectrum is isolated using the coda-source normalization method, which corrects the Lg spectral amplitude for the source using the stable, coda-derived source spectra. Tomographic images of Northern California agree well with one-dimensional (1-D) Lg Q estimated from five different methods. We note that there is some tendency for tomographic smoothing to increase Q relative to targeted 1-D methods. For example, in the San Francisco Bay Area, which contains high attenuation relative to the rest of the region, Q is overestimated by tilde 30. Coda-source normalized attenuation tomography is also carried out for the Yellow Sea/Korean Peninsula (YSKP), where output parameters (site, source, and path terms) are compared with those from the amplitude tomography method of Phillips et al. (2005), as well as with a new method that ties the source term to the magnitude and distance amplitude corrections (MDAC) formulation (Walter and Taylor, 2001). The source terms show similar scatter between coda-source corrected and MDAC source perturbation methods, whereas the amplitude method has the greatest correlation with estimated true-source magnitude. The coda-source better represents the source spectra compared to the estimated magnitude and could be the cause of the scatter. The similarity in the source terms between the coda-source and MDAC-linked methods shows that the latter method may approximate the effect of the former, and therefore could be useful in regions without coda-derived sources. The site terms from the MDAC-linked method correlate slightly with global Vs30 measurements. While the coda-source and amplitude ratio methods do not correlate with Vs30 measurements, they do correlate with one another, which provides confidence that the two methods are consistent.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 2008
- Accession Number
- ADA518070
Entities
People
- Douglas S. Dreger
- Juca Malagnini
- Kevin Mayeda
- Sean R. Ford
- William R. Walter
- William S. Phillips
Organizations
- Lawrence Livermore National Laboratory