Figure 3. Graphical interpretation of Table 1—peak rooftop acceleration (accn) amplitude versus frequency, log scaling. For both east–west and north–south, the best-fitting least-squares solution for all the data is plotted in dashed lines. Outlying data from tests and earthquakes prior to main permanent natural frequency shift (pre-Whittier Narrows for north–south; pre-San Fernando for east–west) are removed from dataset for the solid-line regressions, with labeled functional form.