Seismological Society of America Medal
James Neil Brune

April 10, 1997

The Seismological Society of America Medal has been awarded to those persons whose scientific contributions bolster the overall field of earthquake science and engineering. Previous recipients share many traits-among those is the drive to answer the fundamental questions. Success is measured in the number of times these individuals have answered the ever-present question, "Why?" or made the rest of our community search for answers.

This year's recipient, James Neil Brune, is certainly one who has answered many such questions and at the same time forced all of us to look deeper into the nature of our science. Jim's mentors, colleagues and students have universally commented on Jim's deep intuitive approach for addressing fundamental problems. Phrases such as "extraordinary intuitive sense" or "incredible strength of his intuition and the sharpness of his reasoning" or "remarkable physical insight" are used to describe Jim's approach to science. In a nominating letter for the SSA medal, the author wrote, "His approach to the science of seismology is a highly creative combination of seismic observation, field observation, experimental modeling and theory. He has shown a consistent, uncanny ability to conceive experiments which connect observations directly to the essential physics of seismic phenomena."

Let us reflect for a moment on some of the milestones represented in the more than 160 publications Jim has contributed over the past 38 years. These publications reflect another hallmark of Jim's science: collaboration. Jim has shared his work and ideas with more than 151 individuals including mentors, colleagues and students. In the interest of time I cannot possibly mention all of these individuals.

Jim began his college education as an undergraduate at the University of Nevada, Reno, where he earned a B.Sc. in engineering geology in 1956. Interestingly he has come full circle now serving as Director of the Seismological Laboratory of the Mackay School of Mines at UNR. In his PhD studies at Lamont Doherty Geological Observatory (as it was known in then) Jim developed an interest in the study of the earth's crust and upper mantle using surface waves and he has maintained that interest. Among his discoveries were a simplified method of extracting phase velocity from the seismograms; an explanation for the polar phase shift, the attenuation of surface waves and later the ray-mode equivalence for the explanation of surface waves. He has used surface waves to determine the crust structure of the Pacific, to find a crustal model of the Canadian shield, and to discover the incredible crustal thickness of the sediments of the Bay of Bengal.

Some of the mathematics in his earlier papers contradict the notion that Jim's approach is purely intuitive. I once asked Jim about how he reached his conclusion about using the method of asymptotic expansions to determine the polar phase shift in surface waves. He told me that he didn't derive it first; he measured it first. Jim said that he was in charge of Lamont's laboratory equipment used for teaching. In the basement there was a large steel sphere. So he put a ring of transducers on the sphere and hit it with a hammer. He saw the phase shift: nothing like a direct measurement.

During the 1960's plate tectonics was revolutionizing the earth sciences. Jim left one center of this revolution for another, Caltech, where he became an associate professor in 1965. In a 1968 paper Jim seized the moment (pun intended) to link observations of seismic moment and plate velocities. By summing seismic moments of earthquakes on plate boundaries one could determine the relative motion between plates. This simple concept has had far ranging effects in that it is the fundamental tenet for seismic gaps on a global scale and probabilistic seismic hazard analysis on a regional scale.

Jim knew that plate tectonics was more than a hypothesis and realized the importance of making measurements closest to the source. So in 1969 he initiated a joint seismic network with Mexican seismologists, in particular, Cinna Lomnitz, to measure earthquakes in the Gulf of California, the spreading center for the San Andreas system. Always curious about the orthogonal ridge-transform pattern, Jim once again decided on a direct measurement. With Doug Oldenburg he used a molten wax model to demonstrate how this ridge-transform pattern naturally emerges from the kinematics of the plate motion and the thermal regime of a cooling surface over a hot substrate.
I have it from the most authoritative source-Jim's wonderful wife Sue-that Jim got the idea for the wax experiment while his children were making Christmas candles. With childlike curiosity Jim started experimenting with the molten wax and noted the various patterns that would develop. I don't think he made any useful candles, but the story illustrates, once again, Jim's ability to see beyond the obvious.

Perhaps there is no area of earthquake research that Jim has had a more profound effect than in the study of the earthquake source itself. Today we take it for granted that earthquakes are complex events with heterogeneous distributions of slip. Among the first papers to examine heterogeneity were the 1967 paper with Max Wyss on the Alaskan earthquake and the 1970 paper with Mihailo Trifunac on the complex stress release of the 1940 El Centro earthquake.

It was well known that seismic radiation could not determine the absolute level of stress on the fault. In a classic 1969 paper with Tom Henyey and Rob Roy, Jim presented the "heat flow paradox." Realizing that friction during earthquakes would generate heat, they showed that faulting should produce a heat flow signature proportional to the absolute stress acting on the fault. Laboratory results suggested kilobar levels of stress. However, the heat flow anomaly across the San Andreas limited the absolute stress to a couple hundred bars. The paradox remains today. In looking at Jim's papers it is apparent that he has tried to examine this question from every perspective. He has written papers on low-stress drop earthquakes, high-stress drop earthquakes, frictional melting, interface waves and laboratory models.

If there is any one paper with which Jim is identified it is his 1970 paper "Tectonic Stress and the Spectra of Seismic Shear Waves From Earthquakes." This paper has been cited so often, with respect to the size of the field, that in 1987 the editors of the Scientific Citation Index dubbed it a Citation Classic. This paper provides a fundamental basis for connecting seismic observable-the amplitude spectrum-with earthquake parameters: the dynamic stress that drives the earthquake and the spatial extent of the fault. This paper has been at the heart of innumerable papers on scaling properties for earthquakes, Green's function summation, crustal attenuation, explosion/earthquake discrimination, dynamic earthquake modeling and strong ground motion estimation. It is certainly one of the most influential papers of all time in seismology.

In this era of Gigaflop CPUs, terabyte disks, and gigabytes of RAM, Jim has never strayed too far from his roots. While he encouraged his students to dive into the digital world, Jim always wanted to have experiments where there was less control over the input parameters. In 1972 Jim started a series of experiments using foam rubber as an analog for the earth. I was his first student to work on the foam rubber modeling. After I had graduated and had done both foam rubber modeling and computer modeling, I finally got the courage to ask Jim why he wanted to stay with foam rubber modeling because computer modeling looked promising and allowed for more variety of the input parameters. His reply was simple. He said something like, "The foam rubber models are my analog computers. The results are real without any frequency limitations." Jim has pursued his love of models and, primarily with Rasool Anooshehpoor, produced some exciting and unexpected results about the nature of faulting and the way in which we think of two surfaces sliding past each other. Yes, there are computer models now reproducing and extending the ideas that were first observed in Jim's analog computers.

Whether in the lab or in the field Jim has always pushed for better and better data. I have alluded to some areas, such as the development of the seismograph array in northern Mexico and Baja California, where Jim was the first or among the first to recognize the need for better data. At his instigation other critical projects were launched. For example, Jim and Brian Tucker were the first to deploy digital recorders in an aftershock sequence. Jim and Bill Prothero initiated the ocean bottom seismograph program at IGPP/Scripps Institution of Oceanography. In the mid-eighties the telemetered, digital array at Anza, California, was initiated in a collaborative project between IGPP (Jon Berger, Frank Vernon and Jim) and the USGS (Joe Fletcher, Tom Hanks and Larry Baker). Finally, there was the deployment of the Guerrero strong-motion array spearheaded by Roberto Quaas, Jorge Prince, Sri Krishna Singh in Mexico and John Anderson and Jim in the US. From the recordings of microearthquakes on the mid-ocean ridges to the accelerograms from the great Michoacan earthquake these programs have directly influenced the scope of our science.

I would certainly be remiss if I did not call attention to Jim's continuous collaborative efforts in earthquake research in Mexico. Starting with the seismograph array in 1969, the digital accelerograph array in Mexicali Valley, the present northern Baja California array and the Guerrero strong motion array, Jim has maintained his collaboration for nearly 30 years. It's more than just instruments and data. Jim is a fully vested partner in the education of Mexican students and the evolving seismological research programs. Cinna Lomnitz once wrote, "What Jim has done for Mexican geophysics is surely beyond precedent."

Surely, this legacy of papers and projects is enough to warrant the awarding of the SSA medal to Jim to go with the many other honors, such as AGU's first J. B. MacIlwane Award, the Arthur L. Day Award, Fellow of the Geological Society of America, Fellow of the Indian Geophysical Union, Fellow of the American Geophysical Union, Nomination to the Academy of Creative Endeavors in the Soviet Union, past president of the Seismological Society of America and recently has been named University of Nevada Foundation Professor.

There is more. Jim's legacy is more than a collection of papers filled with innovative and seminal ideas. For everyone who has ever worked with Jim there is the human side of science. To the 21 or more PhD students, the numerous post-doctoral researchers and all of his colleagues there has been a basic tenet of his research that is the equivalent of a medical doctor's first principle: do no harm. When San Onofre nuclear power plant was under review, Jim gave testimony for those who were opposed. When asked why, his reply was that the licensee had plenty of experts but in order to have an open exchange of ideas, the opponents also needed experts to question the assumptions. There are others who know that Jim has always maintained his principles throughout his illustrious career. This side of Jim is best summed up in one of the nominating letters. The author wrote, "Those who have been fortunate enough to know and work with Jim have been inspired above all by his unrelenting commitment to principle and his determination that science serve as a positive moral force."

Today we might say that the Seismological Society of America honors one of its finest members. In truth, it is Jim Brune who honors us by accepting the Medal of the Seismological Society of America.

Ladies and gentlemen, it is my greatest honor, on behalf of all of us, to present the Seismological Society of America Medal to James Neil Brune.