Resolving Earth's Free Oscillation Spectrum: New Data and New Techniques

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9508113 GILBERT This research involves the complete re-evaluation of the Earth's complete normal-mode spectrum in light of recent large earthquakes. It is fair to say that, before the June 9, 1994, great deep Bolivian earthquake, observational free-oscillation seismology had gone into a state of suspended animation. A lack of very large events and, in particular, the lack of very large deep events made progress difficult and incremental. The Fiji event in March rekindled some interest since it was the largest deep event to be digitally recorded since the 1970 Columbian event, but it was rapidly eclipsed by the Bolivian event. Not only was the Bolivian event bigger than the 1970 Columbian event but it was recorded by an unprecedented number of observatory-quality digital stations. For those who know what is possible with hand-digitized recordings of the Columbian event, the new data promise a quantum improvement in our knowledge of the seismic response of the Earth at long-periods. It is anticipated that this research will lead to, at the minimum: stringent constraints on anisotropy in the core, constraints on the relative P and S velocity variations in the mantle, constraints on 3-D attenuation structure (at least of even harmonic degree), high resolution 1-D models with resolution lengths below 100 km for precisians of 0.1%, and an accurate description of the seismic spectrum at long periods making better determination of long-period source behavior for large events possible. *** ??