(b). Yamaguchi, Japan, 21 August 1895; d. Tokyo, Japan, 23 April 1944)
applied mathematics, theoretical seismology.
The son of a judge, Sezawa entered the Imperial University of Tokyo in 1918 and graduated as a shipbuilding engineer in 1921. He was then appointed assistant professor of engineering at the university and became a full professor in 1928. He first worked on problems of shipbuilding engineering and of vibration, in which he acquired a considerable reputation. In 1925 he started a lifelong association with the Earthquake Research Institute of the university, becoming its director in 1943. In 1932 he visited Britain, Germany, and the United States to further his studies in theoretical seismology, the field in which he is now best known. Sezawa was associated with many Japanese research organizations, including the Seismological Society of Japan, the Aeronautical Research Institute, and the Aviation Council, During World War II his responsibilities were greatly extended; he was supervisor of research projects at the Admiralty and a member of the Air Force Weapons Research Committee and was closely connected with army research.
when Sezawa began his research career, the new science of seismology presented challenging problems requiring sophisticated mathematical analysis. Sezawa’s pioneering work on many of these provided the basis for important later developments both in Japan and elsewhere and his mathematical ability was a significant factor in raising the world standard of seismoiogical research. Much of this work was carried out in collaboration with his brilliant former pupil Kiyoshi Kanai.
Sezawa is particularly noted for his contributions to the theory of seismic surface waves, one of the main wave types generated by earthquakes. These waves tend to become increasingly regular in form as they move away from an earthquake source. Mathematical analysis of this property throws light on the structure of the outer part of the earth. By this means Sezawa derived useful estimates of layering in the earth’s crust and produced evidence indicating that the Pacific curst is thinner than the Eurasian. More profoundly, his work pointed the way to important developments of the existing mathematical theory of seismic surface waves.
Sezawa produced a body of theory important to such seismological problems as seiches in lakes and tsunami (seismic sea waves) generated by large earthquakes, and the mechanism of earthquake generation. He applied his earlier studies of vibration theory to the problems of vibrations excited in buildings and bridges by strong earthquakes, contributed to the theory of designing structures to withstand earthquakes, and participated in related experimental work.
Although he was often unwell, Sezawa drove himself hard and lived very austerely. His health deteriorated seriously during the war, and he died at the age of forty-eight. The Imperial Academy of Sciences of Japan awarded him its highest honor, the Imperial Order of Merit, in 1931 and elected him a member in 1943.
Most of Sezawa’s 140 research papers on seismology and earthquake engineering were published as Bulletins of the Earthquake Research Institute of Tokyo Imperial University. Forty-six of his more important papers are listed in W. M. Ewing, W. S. Jardetzky, and F. Press, Elastic Waves in Layered Media (New York, 1957). He also wrote 50 papers on aeronautics, published in Reports of the Aeronautical Research Institute. Tokyo University; and 20 papers on ship construction, published as Reports of the Society of Naval Architecture of Japan.
An obituary was published in Japanese in Jishin. 16 no. 5 (May 1944), 1–2.
K. E. Bullen