Presidential Young Investigator: Seismology

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Observations of the earth's free oscillations and the seismic structure of the earth's interior. Improved algorithms are required to resolve lateral structure to the accuracy and resolution required to make definitive judgements on deep earth geology and thermal structure. Current studies of upper mantle structure using low-frequency ( 5mHz) surface waves have used inversion algorithms that are valid only for long-wavelength ( 4000km) aspherical structure. Dr. Park has developed an asymptotic coupled-mode formalism that is valid for weak perturbations at all wavelengths. He intends to pursue both a long-wavelength inversion using this technique and a "controlled" synthetic-seismogram study of the effects on low- frequency waveforms of "sharp" lateral gradients in seismic structure e.g., continent-ocean boundaries. These projects will entail the use of advanced computer hardware available through Yale's Computer Science Department and the NSF supercomputer centers. The spectral content of high frequency seismic codas caused by reverberations in the crust. Preliminary investigations of frequency-dependent particle-motion polarization suggest that many codas decompose into distinct waveguide resonances with independent propagation histories. Dr. Park anticipates further collaborative research using existing regional array data, with application in lithospheric structure problems and seismic test-ban discrimination questions.