75th anniversary of strong motion observation—A historical review

This review describes the experience accumulated in the field of recording earthquake motions up to the early 1900s, and then it discusses the key players who contributed to the first successful strong motion observation program in earthquake engineering in the 1930s. It begins by summarizing the accomplishments of the preceding seismological observations, which provided the stepping-stone ideas on how to construct the first strong motion accelerograph. Next, it describes the lack of optimism among the engineers in the early 1900s, who doubted that structural response could ever be calculated for irregular earthquake ground motion—this was, of course, half a century before the appearance of fast digital computers—but also their realization that something needed to be done to reduce the hazards from earthquakes. The roles of the two pioneers Kyoji Suyehiro and John Freeman, whose vision, leadership, and perseverance launched the strong motion observation program in 1932, are then briefly discussed. Finally, the mechanical characteristics of the first strong motion accelerograph are outlined. The review is completed by illustrating the growth of the strong motion observation programs in selected seismic areas of the world and the fruits of these programs—the cumulative number of uniformly processed strong motion records in southern California.