Memorial: Keith Edward Bullen

by
Bruce A. Bolt
Seismograph Station
University of California
Berkeley, California

Keith Edward Bullen, Fellow of the Australian Academy and Fellow of the Royal Society, was born on June 29, 1906, in New Zealand where he received his early education.

" I had the outstanding good fortune to be taken in hand by Sir Harold Jeffreys, who literally brought me down to Earth and rescued me from a pure mathematical fate. "

On February 2, 1931, while he was lecturer in mathematics at Auckland University College, the Hawke's Bay earthquake occurred, and it stimulated his life-long interest in seismology. He spent 1931 through 1933 at St. John's College, Cambridge, England, where in Bullen's own words, "I had the outstanding good fortune to be taken in hand by Sir Harold Jeffreys, who literally brought me down to Earth and rescued me from a pure mathematical fate." Bullen returned to teach at New Zealand University in 1934 and made his permanent move to Australia in 1940 when he was appointed as a senior lecturer in mathematics at the University of Melbourne. It was at Melbourne that he wrote his famous book, Introduction to the Theory of Seismology, base in part on lecture courses which he gave on vibrations and waves and elasticity.

Forty years ago, only crude estimates of the density distribution in our own planet were available. In 1923, L.H. Adams and E.D. Williamson realized that observable seismic velocities allowed the density variation to be estimated for a homogeneous, adiabatic shell. Bullen molded the method to conform to much more precise velocity values calculated by Jeffrys from new seismic traveltimes, measured jointly by Jeffreys and Bullen. Until his death in 1976 in Auckland, New Zealand, on September 23, Professor Bullen continued this unrivaled analysis of the interaction between seismic travel times and the physical properties of the interiors of the terrestrial planets.

Bullen's reputation had been made by the publication of the Jeffreys-Bullen Seismological Tables in 1940, adopted for calculations for the International Seismological Summary from 1937 onward and still used by the main centers of seismicity analysis. By 1950, his reputation had been further increased by publication of his Introduction to the Theory of Seismology, and he then made journeys as an Australian delegate to international conferences. In 1963, he was elected vice president of the International Union of Geodesy and Geophysics. He much enjoyed these travels, although he once told me that there was an advantage in being somewhat isolated in Sydney where he could develop original work untrammeled by the pressures of group effort.

For these lasting contributions, he received many honors from the scientific community. He was modest about his research (recently declining an offer to develop for publication his collected works of over 250 papers and articles). But he was justifiably proud of the style and clarity which he strove to attain in the verbal and written expositions of his studies. He alluded to the problem of orderly evolution of scientific knowledge in his last book, The Earth's Density (1975). This fine historical evaluation of studies of the density of the Earth stands as a monument to his own endeavors.

Bullen had always been a noted walker and possessed great skill at table tennis. After his retirement, he had written to me that he wished to write two or three other books. It was evident that Bullen assumed that he would have many more years of activity ahead. Unhappily for his many friends and colleagues around the world, he did not live to finish these enterprises.

Abridged from Earthquake Information Bulletin, September - October 1977, Volume 9, Number 5.