A mutually consistent seismic-hazard source model for southern California

A previous attempt to integrate geological, geodetic, and observed seismici ty data into a probabilistic-hazard source model predicted a rate of magnit ude 6 to 7 earthquakes significantly greater than that observed historicall y. One explanation was that the discrepancy, or apparent earthquake deficit , is an artifact of the upper magnitude limit built into the model. This wa s controversial, however, because removing the discrepancy required earthqu akes larger than are seen in the geological record and larger than implied from empirical relationships between fault dimension and magnitude. Althoug h several articles have addressed this issue, an alternative, integrated so urce model without an apparent deficit has not yet appeared. We present a s imple geologically based approach for constructing such a model that agrees well with the historical record and does not invoke any unsubstantiated ph enomena. The following factors are found to be influential: the b-value and minimum magnitude applied to Gutenberg-Richter seismicity; the percentage of moment released in characteristic earthquakes; a round-off error in the moment-magnitude definition; bias due to historical catalog incompleteness; careful adherence to the conservation of seismic moment rate; uncertainty in magnitude estimates obtained from empirical regressions; allowing multi- segment ruptures (cascades); and the time dependence of recurrence rates. T he previous apparent deficit is shown to have resulted from a combination o f these factors. None alone caused the problem nor solves it. The model pre sented here is relatively robust with respect to these factors.