J. Freeman Gilbert

1999 William Bowie Medal Winner

University of California

J. Freeman Gilbert was awarded the William Bowie Medal at the AGU Spring Meeting Honors Ceremony, which was held on June 2, 1999, in Boston, Massachusetts. The medal recognizes outstanding contributions to fundamental geophysics and unselfish cooperation in research.


“Freeman Gilbert was a geophysical pioneer, even as a student at the Massachusetts Institute of Technology, where he used the Whirlwind computer to apply computational methods to seismic problems. Later at the Institute of Geophysics and Planetary Physics (IGPP), at the University of California, Los Angeles, where he began his professional university career, he wrote a series of papers on the computation of synthetic seismograms in simple media. While at UCLA he developed the idea of expressing seismic motion in terms of the free oscillations of the Earth. He continued this work after moving to the La Jolla branch of IGPP, and through a very productive collaboration with Adam Dziewonski, applied these ideas with extraordinary effect first to seismic records from the 1964 Alaska earthquake and then to records from the remarkable 1970 Colombian earthquake. The moment tensor description of the seismic source that Gilbert developed at this time revolutionized the way earthquakes are analyzed. The data set of free oscillation frequencies that Gilbert and Dziewonski identified formed the main database from which early reference Earth models (1066A+B and PREM) were built. This database led to many important findings, not least of which is unambiguous evidence that the inner core is indeed solid!

“In the mid-1960s at IGPP, Freeman Gilbert and George Backus collaborated on a brilliant series of papers in an area that was to become known as geophysical inverse theory. Clearly, Freeman and George are the fathers of this field and the research they did at this time changed the course of the geophysical sciences, broadly defined, forever.

“By the late 1960s, it was apparent that the currently available World Wide Standardized Seismographic Network (WWSSN) was no longer able to provide data of the quality needed to advance the field of seismology. Gilbert, through his close relationship with Cecil Green, convinced Green that we needed a modern network of seismographs that would provide the data necessary for global studies of the Earth. The first of 40 stations of the International Deployment of Accelerometers (IDA) ARRAY–the acronym also commemorates Ida Green!–was installed in Australia in 1974, and the data obtained ever since are available to all. Much of Gilbert’s most recent work addresses the attenuation of mechanical energy in the Earth, as deduced from observations of the broadening of the free vibration resonances of the whole Earth.

“Freeman Gilbert has acted as advisor and mentor to many fine seismologists in the United States including Jon Berger, Ray Buland, Ben Chao, Tony Dahlen, Don Helmberger, Guy Masters, and Jeffrey Park. This is an enviable record and clearly demonstrates his prowess as a teacher. He has served as Chairman of the Earth Sciences Board of the National Research Council. Gilbert was largely responsible for starting the supercomputer center at the University of California, San Diego in the late 1980s, and he played a large role in formulating the proposal for the National Partnership for Advanced Computational Infrastructure (NPACI) at the Scripps Institution of Oceanography and 29 other universities and laboratories.

“In all these ventures Freeman Gilbert has demonstrated the qualities that make him the ideal recipient of the Bowie Medal.”

—KARL K. TUREKIAN, Yale University, New Haven, Conn., USA


“Let me begin with the traditional ending. My life as a scientist has been strongly influenced by my family. The balance between the intensity of research and the personal interaction with my wife and children has led to a steady course. Yes, there have been obstacles along the way, but the sunny days have outnumbered the cloudy ones by far.

“Karl Turekian is deservedly well known for his generosity of spirit and word, both of which are evident in his citation, for which I am very grateful.

“The letter from John Knauss informing me that I had been selected to receive the Bowie medal left me surprised and pleased, and I tried to recollect the sequence of events that had led to that communication. I have decided that the primary explanation is the variation in the length of day. Let me clarify my remark.

“In 1957, I was a postdoc at the Institute of Geophysics (IGPP) at The University of California, Los Angeles, learning primarily from Leon Knopoff how to be a research scientist. One day I met a youngish man, half a generation older than I, from the Scripps Institution of Oceanography. He was working with Gordon MacDonald on a monograph on the rotation of the Earth. When I first met him he was barefoot, nearly shirtless, and irreverent, but friendly and inquisitive. I am, of course, describing Walter Munk. In 1959, both Harvard and the Massachusetts Institute of Technology attempted to hire Walter. Roger Revelle wanted to retain him. The price was permission to establish a branch of IGPP at Scripps plus a few faculty positions. Among Walter’s first appointments were George Backus, from MIT, and Klaus Hasslemann, from Hamburg. Another was myself, then at Texas Instruments. Yet, had it not been for Walter’s study of the variation in the length of day, I probably would not have met him in the late 1950s and would not have come to Scripps.

“At Scripps, George Backus and I began our collaboration on geophysical inverse problems. Sources of inspiration included the prospecting work of the Schlumberger brothers, the theoretical work in electrical engineering on synthesizing circuits to have a desired driving point impedance, and the work of Russian mathematicians on the determination of an ordinary differential equation from its spectrum. George and I had a sort of “odds-and-ends” education that enabled unorthodox thinking and motivated our research.

“Let me give you a few more examples of the importance of good colleagues for whom I have great respect. One is the set of Jim Brune’s provocative questions that led to the moment tensor formalism. Another is the dedication of a graduate student, now the quite mature Bill Farrell, that led to a superb digital recording of the Colombian earthquake of July 31, 1970. This, in turn, led to Project IDA, named in honor of the wife of Cecil Green. It also led to my collaboration with Adam Dziewonski on Earth models and earthquake sources, one result of which was the demonstration that the inner core of the Earth is solid. Very good digital data from the IDA network led to the discovery of anomalous splitting by Guy Masters and to the discovery of the large, aspherical structure in the mantle by Guy Masters and Paul Silver. More recent developments include the matrix autoregressive methods for three-dimensional structure and sources.

“In brief, my good fortune is that I have been in the right place at the right time, with good facilities and excellent colleagues. John Donne has written, ‘No man is an island, entire of itself’; I can only say that I heartily agree.”

—J. FREEMAN GILBERT, Institute of Geophysics and Planetary Physics, University of California, San Diego, USA