Figure 4. East–west components of CR-1 array in Millikan Library, recorded during the M 6.1 Whittier Narrows earthquake = 19 km, velocity time series. The top trace is from the basement, the second is from the sixth floor, and the last two are from the roof. The last trace includes a sample of how the fundamental frequency of the building is estimated, after the main energy (seen from the basement trace) has passed.