Figure 8. Deviation from the mean natural frequency for the three fundamental frequencies at MIK, May 2001 through November 2003. Fundamental frequencies for each hourly FFT are picked from the peaks in Figure 6, then the deviation from the average is determined. The hourly peak is shown in the thin green line for each frequency; the thick black line tracks the daily average. The thick red horizontal line is the average frequency. Daily rainfall (black), maximum wind gust (green), and maximum temperature (red) from JPL are plotted at the bottom. Vertical blue dashed-dot and red dashed lines indicate days with forced vibration shaking of the library, and earthquakes with motions exceeding 2.5 cm/sec² at station MIK, respectively, which produce large deviations from the mean (Earthquakes: 9/9/01, M 4.2 Beverly Hills, 7 cm/sec²; 30/10/01, M 6.1 Anza, 2.8 cm/sec²; 3/9/02, M 4.8 Yorba Linda, 5 cm/sec²; 22/2/03, M 5.4 Big Bear, 18 cm/sec²) Note: forced vibration with full weights generates 8 cm/sec² at north–south fundamental mode.