Bulletin of the Seismological Society of America; February 2006; v. 96; no. 1;
p. 313-320; DOI: 10.1785/0120050053
© Seismological Society of America
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Figure 6. The left column shows (a) the number of M 3+ earthquakes per
year, (b) the estimated background fraction, and (c) the resulting background
rate in different regions of size 100 x 100 km in California. In each
plot, the points indicate the values for the complete data set, whereas the bars
show the span of values resulting from four different subsets. The time
intervals of the subsets are 1980–2000, 1980–1990, 1990– 2000,
and 1990–2004, respectively. For the complete data set, (d) shows a map of
the estimated mainshock rate. In this case, we used circular regions with radius
50 km instead of square regions. White spots above 32.5° latitude are
regions where less than 50 events with M 
3 occurred since 1980 in a
distance less than 50 km.
