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 13. Acceleration data and resulting spectrograms for MIK from 22
February 2003. M 5.4 Big Bear earthquake occurs at 12:19 UTC. Maximum
acceleration = 19.3 cm/sec2 north–south, 10.9
cm/sec2 east–west. Spectrograms are set around the four natural
frequencies. (a) 12:00–13:00 UTC, 30-sec-window spectrograms, with slices
shifted by 15 sec. The natural frequencies shorten considerably during the
mainshock shaking and aftershocks. Analysis of long-term behavior, especially
that of the second mode east–west, is limited by poor resolution due to
short FFT length. (b) 11:30–14:30 UTC, 5-min window
spectrograms, with slices shifted by 1 min. After shaking has dissipated, over
this time window it is clear there is no perceptible long-term shortening of the
fundamental frequencies due to the earthquake. The event at 168 min is a
M 4.1 aftershock.
