On several recent occasions the author has made the statement that
in California the geologist is in a somewhat better position than is
the seismologist to delineate areas of high seismic hazard from great
earthquakes, simply because of the inadequacy of the statistical sample
based on the relatively short seismic history as compared to the
much greater time span that the geologist is able to interpret from the
Quaternary geologic history. A number of recent studies have pointed
out the lack of correlation between areas of current seismic activity
and areas of great earthquakes in the historic past (Niazi, 1964; Allen
and others, 1965; Ryall and others, 1966; Brune and Allen, 1967a). The
purpose of this paper is to go one step further and ask if the geologist
can say anything about the maximum size of earthquakes that might be
generated in any area on the basis of its distinctive geologic features.
More specifically, are different segments of the San Andreas fault-which
currently show markedly varying mechanisms of strain release
ranging from continuous creep to infrequent great earthquakes--characterized
by contrasting geologic features that might suggest that these
differences in current behavior are permanent rather than temporary
characteristics of these individual fault segments? That is, are there
geologic features that might somehow allow us to predict that some segments
of the fault will be the repeated sites of great earthquakes,
whereas other segments might never experience great earthquakes but
instead be characterized by continuous creep or by numerous smaller
shocks? If those same segments of the fault that show distinctive
strain-release characteristics also show distinctive geologic characteristics,
then one must suspect that the answer to this question is
indeed "yes," although such an affirmative answer must be contingent
on a demonstration that this is mechanically reasonable and possible
