Figure 3. Average rate of earthquakes in four magnitude ranges, as a function of catalog duration, where a y-year average is based on the most recent y years of the catalog ending 31 December 1999. Magnitude ranges are: (a) 4.8 M 5.4; (b) 5.5 M 5.9; (c) 6.0 M 6.9; (d) M 7.0. The duration of catalog completeness is estimated from the point at which the rate of earthquakes falls off (shown by arrows). Horizontal dotted lines indicate the upper and lower range of the earthquake rates. Completeness durations determined from these figures are applied to smaller magnitude intervals to generate the occurrence rates shown in Figure 4.