this report. Consequently, detailed site analyses may require
modification of the conclusions reached in this report, particularly
fault systems other than the San Andreas and Hayward faults.


B. GEOLOGIC EVIDENCE

Some of the possible earthquakes listed are repeat occurrences of
historical events, others are not, but geologic evidence indicates
that earthquakes occurred on these faults before settlement of the
region. Based on available data, the postulated earthquake magnitudes
would be the largest events that could be expected at a reasonable
level of probability. They represent a selection of events useful for
planning purposes, but are by no means the only such events likely to
occur either on these or other fault systems.

The historic record of seismicity in California is too short to
determine confidently how often large earthquakes reoccur. Information
on past earthquakes must be gleaned from the geologic record and
therefore, presents a picture of past seismicity that is incomplete
and not yet fully deciphered. Current knowledge about the recurrence
of large earthquakes on specific faults is rudimentary. The
probabilities of occurrence shown above are order-of-magnitude
estimates and subject to considerable uncertainty, especially for the
less probable events.


C. DESCRIPTION OF EVENTS

Following are brief descriptions of postulated events. Figure 1 gives