FIGURE 2.17 Accelerogram of the 1940 Imperial Valley earthquake (center panel), schematic representation of the response of a series of single degree-of-freedom oscillators having different natural periods (top), and their application to the construction of the response spectrum (bottom panel). SOURCE: H.B. Seed and I.M. Idriss, Ground Motions and Soil Liquefaction During Earthquakes, Earthquake Engineering Research Institute, Engineering Monograph on Earthquake Criteria, Structural Design, and Strong Motion Records 5, El Cerrito, Calif., 134 pp., 1982.