Investigations of Eurasian Seismic Sources and Upper Mantle Structure
Abstract
We formulated a new set of waveform-analysis procedures to recover phase and amplitude information from seismograms. These procedures appear to be capable of making fundamentally new observations about the structure of the earth's interior. We used them to measure travel times and quality factors of body waves, including those embedded in complex wavetrains, as well as dispersion and attenuation of surface waves, including higher modes. We applied these techniques to three-component seismograms to investigate the structure of the Eurasian upper mantle, made observations of shear-wave splitting on long period records of multiply reflected S waves bottoming in the upper mantle beneath the Russian and Siberian platforms. Dispersion of Love and Rayleigh waves over these paths shows discrepancies of comparable or larger magnitude with respect to smooth isotropic structures, consistent with a model of the uppermost mantle having significant apparent vertical anisotropy. Although the splitting and dispersion data can be fit by smooth anisotropic models, we investigated the apparent anisotropy associated with fine-scale ('rough') structure beneath stable Eurasia. We fit the data with a rough isotropic model having an rms shear velocity fluctuation that varies from 14% in the uppermost mantle to zero at 400-km depth. The fluctuations are larger than the variation expected for even a diverse assemblage of upper-mantle ultrabasic rocks, which we take as evidence for some sort of intrinsic (local) anisotropy.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 25, 1989
- Accession Number
- ADA211806
Entities
People
- Justin S. Revenaugh
- Lind S. Gee
- Thomas H. Jordan
Organizations
- Massachusetts Institute of Technology