(v)

A comprehensive review of the conditions that prepared the key players to create the concept of the response spectrum method is beyond the scope of this brief introduction. Thus, I will mention only a few examples. First, the teaching of physics, and, in particular, of engineering mechanics and applied mathematics, started to expand in Europe around the end of 19th and the beginning of 20th century (Timoshenko, 1968; von Karman and Edson, 1967; Cornwell, 2003). Second, several earthquake disasters (in 1906, 1908, and 1923) in densely populated areas made it clear that defensive mechanisms needed to be developed to prevent future loss of life and property from destructive earthquakes. Third, the arrival of leading scientists and engineers in earthquake-prone areas (e.g., Milne in Japan; Compte de Montessus de Ballore in Chile; Millikan, Gutenberg, and von Karman in Southern California), and their organizational abilities, interest, and curiosity to examine yet another challenging group of physical phenomena, created new critical mass and organization, which in turn attracted the next generation of talented students. The first practical steps which initiated the engineering work on the design of earthquake-resistant structures accompanied the introduction of the seismic coefficient (shindo in Japan, and rapporto sismico in Italy, for example), which started to appear following the destructive earthquakes in San Francisco