This map shows the seismicity of southern California from 1983 to 1997, with each colored pixel representing the epicenter of one earthquake. (In some places, earthquakes overlap.) The color of each epicenter is based upon its location relative to the surface traces of potentially active faults. The color scale used is shown at upper right. The distribution of slip rates in southern California is far from linear, and the non-linear (logarithmic) color scale reflects this.
Each epicenter was given the color corresponding to the slip rate of the nearest fault trace. Because of this, seismicity along dipping faults (including the thrusts and blind thrusts of the Los Angeles Basin area) may be miscolored if the seismicity occurred in a way that their epicenters are closer to the surface trace of another fault. Thus, this map is not intended to be an accurate picture of exactly which earthquakes occurred on which faults, but instead is meant to be a general guide to the correlation between slip rates and seismicity rates. The slip rates and surface traces used for this map were taken directly from this map of slip rates in southern California.
When studying this map, keep in mind that this figure is meant for qualitative, not quantitative, analysis. The slip rates given here are not meant to represent exact figures, but rather a good estimate, often based on several different studies using different methods to determine the rate. Also, the slip rates for many of these faults are unknown, or are likely inaccurate, and there is no information given on the map that applies to the uncertainties in the slip rates given. When insufficient data was available, reasonable assumptions were made to fill in these parts of the diagram.
In addition to these warnings, you should realize that due to the nature and comparitively small number of slip rate studies, the resolution of this map is very low. This means that minor changes in slip along the length of a fault, or along branches of a fault zone, are generally not represented.
Finally, most of these earthquakes did not occur directly on the main fault for which the slip rate is given, but on smaller faults which may or may not be directly influenced by the amount of strain on the nearest primary fault. In general, the farther removed from the surface trace an epicenter is, the less reliable the correlation with slip rate. You may want to refer to the slip rate map to check the locations of the surface traces used in this figure.
