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Geology of Mount Shasta

Figure 25

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Figure 25: Histogram showing the number of quakes per 2 month period beneath Mount Shasta from January 1978 through June 2001. Each ticked interval at the bottom of the histogram represents one year. The apparent increase in seismicity in August 1981 (month 44) is an artifact of the installation of a local seismic network around Mount Shasta at that time. Note the prominent earthquake swarm that occurred in late 1992 and early 1993 (about month 180). Data from the Northern California Earthquake Data Center database.

 

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