Figure 5. Summary of regional rates of M>=6.7 earthquakes inferred from Gutenberg-Richter (G-R) models. The height of each solid horizontal line represents an average rate extrapolated from a G-R model, while its width indicates the time period of the data used. For the 20th century data, two rate estimates for each decadal period�one made with the full catalog (light lines) and one with a declustered catalog (heavy lines)�provide bounds on the estimated contemporary rates, and hence are shown connected with vertical lines. Sloping straight lines are least-squares fits to the rates estimated with the declustered catalog, and are considered lower bounds on the rate trend. The more shallowly sloped line is the fit to all six decades, while the more steeply sloped line is the fit through the last three decades only. Curved line represents the instantaneous rate of M>=6.7 earthquakes expected in a generic California aftershock sequence (Reasenberg and Jones, 1989) following a M=7.8 mainshock in 1906. Heavy dashed line is the mean regional long-term rate of earthquakes on all rupture sources in the calculation sequence, including the "background" source. Light dashed lines are the corresponding 5th and 95th percentile values in the calculation sequence for this quantity. Upper and lower heavy dotted horizontal lines are long-term regional rates estimated, respectively, by Andrews and Schwerer (unpublished manuscript), based on a regional segmentation utilizing Working Group On Northern California Earthquake Potential 1996 fault segments, and Ward (in press), based on a simulated physical earthquake model.