Keiiti Aki (1930-2005)

Abstract

Everyone called him Kei, the intellectual leader who for forty years brought new methods to a more quantitative understanding of dynamic processes within the Earth. Kei Aki died on 17 May this year on Reunion Island, the “hot spot” in the Indian Ocean that had been his home since retirement from academic life in the United States. He will be known for his many research results in seismology as well as for his team leadership in developing probabilistic estimates of seismic hazard.⇓ ![][1] Kei was born in Japan to a family of engineers with a 100-year tradition of education and openness to the West, but then, as he wrote, “When I was 19 years old, I applied to the Department of Geophysics of the University of Tokyo, partly because of the simplest entrance examination, only on three subjects, English, Mathematics and Physics.” He continued there to a Ph.D. thesis on spectra of stationary stochastic seismic waves and briefly held a fellowship at the California Institute of Technology in the early 1960s, where he greatly impressed Charles Richter and Frank Press before returning to the University of Tokyo in 1963. When Press left Caltech to head Earth Sciences at the Massachusetts Institute of Technology, he recruited Kei to the MIT faculty in 1966 and thus to an American academic career. His scientific achievements include some of the earliest studies interpreting the radiation pattern of seismic surface waves to estimate fault orientation and direction of slip at the earthquake source. In 1966 he showed how to estimate the seismic moment of an earthquake from seismograms. This measure, equal to the product of rigidity, fault area ruptured, and average fault slip, became recognized as the best way to characterize the size of an earthquake source and the strength of its long-period waves. Seismic … [1]: /embed/graphic-1.gif