Princeton University
Email:
fad@princeton.edu
poster/oral: oral
| Freeman Gilbert, one of the greatest geophysicists of the twentieth century, was born in Vincennes, Indiana in 1931, and graduated as valedictorian of his high school class in Lawrenceburg, Kentucky in 1949. He received his Bs.C. and Ph.D. degrees from the Massachusetts Institute of Technology in 1953 and 1956, respectively. His Ph.D. dissertation "Seismic wave propagation in a two-layered half-space" was a generalization of Sir Horace Lamb's classic 1904 paper on seismic wave propagation in a one-layer elastic half-space. During his stay at MIT, Freeman contemplated a career in exploration geophysics, prospecting for oil in the delta of the Orinoco River delta and for copper in the southwestern United States. Following his graduation, he spent two years as a research assistant and assistant professor at UCLA, and two years doing research in numerical seismology at Texas Instruments in Dallas. In 1961 he joined the faculty of the Institute of Geophysics and Planetary Physics at the University of California at San Diego, where he has remained to this day. In that same year, Freeman published his first paper with George Backus: an analysis of the rotational splitting of the free oscillations of the earth, which was observed after the great Chile earthquake of May 22, 1960. Between 1967 and 1969, Freeman and George published a series of three papers on geophysical inverse theory, which have had an enormous influence upon an entire generation of seismic tomographers and other geoscientists. Between 1971 and 1975, Freeman joined forces with Adam Dziewonski at Harvard University, to conduct historic analyses of the free oscillations excited by the 1963 Peru-Bolivia, 1964 Alaska, and 1970 Colombia earthquakes. They succeeded in measuring the eigenfrequencies of more than 1000 of the earth's normal modes, and used these to constrain the spherically averaged elastic properties of the earth's interior. Freeman's and Adam's elucidation of the earth's internal structure -- prior to their work it was not certain whether the inner core was liquid or solid -- is arguably an even more celebrated seismological collaboration than that between Sir Harold Jeffreys and Keith Bullen. Starting in 1970 and continuing to the present day, Freeman published approximately one dozen seminal, short, single-author theoretical papers, on a variety of topics ranging from free oscillations to inverse theory to signal analysis. His 1970 paper ``Excitation of the earth's normal modes by earthquake sources" introduced the concept of the moment tensor into seismology, and led ultimately to the highly successful Harvard Centroid Moment Tensor Project, which has measured the source mechanisms of approximately 20,000 earthquakes to date. The fledgling IDA seismic network, which Freeman deployed, together with a number of IGPP collaborators in 1976, helped to spur the development of the IRIS Global Seismic Network, which has grown to more than 120 broadband ststions worldwide. In 1978 Freeman began what is probably his most productive collaboration -- with Guy Masters, then newly arrived at IGPP following his graduation from Cambridge University. Freeman, Guy and a number of excellent IGPP graduate students have relentlessly utilized seismic data from the IDA and IRIS networks to constrain the spherically averaged attenuation structure of the earth's mantle and inner core, and to resolve and interpret the splitting of the earth's free oscillations in terms of rotation, ellipticity, three-dimensional mantle heterogeneity and inner-core anisotropy. In recognition of his many important achievements in geophysics, Freeman was elected to the US National Academy of Sciences in 1973, and was awarded the Gold Medal of the Royal Astronomical Society in 1981, the Arthur L. Day Medal of the GSA in 1985, the Balzan Prize in 1990, and the William Bowie Medal, the highest award of the AGU, in 1999. In his eloquent Bowie Medal citation, Karl Turekian likened Freeman to Quasimodo, who could divine the future by listening to the bells of Notre Dame de Paris. Freeman has spent his distinguished career in an unchanging office in IGPP, listening intently to the ringing of the earth, and using its notes to divine the secrets of its interior. |