Bulletin of the Seismological Society of America; February 2006; v. 96; no. 1;
p. 237-257; DOI: 10.1785/0120050052
© Seismological Society of America
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Figure 7. Spectrogram of all six horizontal channels at station CBC, the Broad Center,
February 2003 through November 2003. One-hour spectrogram windows, no scaling,
linear color bar. Sharp red horizontal lines are due to machine noise in the
building. Natural frequencies are represented by the broad peaks, near 2.6 Hz,
3.0 Hz, and 3.6 Hz, for the east–west channels, and near 2.4 Hz, 2.8 Hz,
and 3.6 Hz for the north–south channels. Notice the 7-day noise cycle with
relative quiet on the weekends.
