Synthesis of Lg in Eastern United States Crustal Models with Frequency Independent
Abstract
The parametric dependence of short period Lg on characteristics of the source and travel path is studied using synthetic seismograms computed by modal superposition. The earth models are plane-layered and laterally homogeneous with a frequency-independent Q, and are meant to represent the eastern United States. The Q and velocity structure of the 34 km thick crust are varied with the upper mantle being represented by a halfspace. Synthetic seismograms that qualitatively match many observed features of eastern United States Lg are computed with 35 to 50 modes in models that include some lower velocity sediments and low Q near the surface. The observations are represented by the LRSM short period recordings of the SALMON nuclear explosion in Mississippi. Three quantitative data features not reproduced by the synthetics are: (1) There is not enough energy at group velocities less than 2.9 km/sec; (2) The synthetic spectra fall off more rapidly above 2.5 Hz than observed spectra from SALMON; (3) The amplitude attenuation with range is much faster than observed in the eastern United States. While some of this may be due to not including the multipathing and scattering that must be present at these high frequencies, the requirement for frequency-dependent Q is strongly indicated.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 1980
- Accession Number
- ADA096340
Entities
People
- B. Shkoller
- H. Swanger
- Thomas C. Bache
Organizations
- Utility Systems Science and Software (United States)