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 14. Acceleration data and spectrograms from CBC east–west channels,
11:30–14:30 UTC. Five-minute window slices, each shifted by 1 min. There
are two spectrograms for each east–west channel; the first is a broad
frequency range from acceleration data showing all identified modal frequencies;
the second is a frequency band around the first mode using displacement data,
which accentuates the behavior of the only mode without nearby machine noise
(see Fig. 7). M 5.4
Big Bear earthquake occurs at 12:19 UTC. Maximum acceleration = 14.8
cm/sec2 at BL6, northwest Roof. During the event, the fundamental
frequencies shorten considerably. After shaking, over this time window there is
no perceptible long-term shortening of the fundamental frequencies due to the
earthquake.
