Tectonics of the San Andreas Fault System geologic studies



Earthquake probability. A long-term rate of right-lateral slip on the San Andreas fault of between 1 and 2 cm/yr over at least the past 25 million years and possibly 60 million years has been further confirmed and defined by recent analyses of offset sedimentary basins [Vedder, 1966; Addicott, 1968; Dibblee, 1966; Cummings, 1968; and Wentworth, 1968]. The data suggest possible variations between these limits in different geologic periods, but data are not yet adequate to define the changes precisely.

These long-term rates are approximately the same as those determined by geodesy and other means. For example, Brown and Wallace [1968] found that an average rate of about 2 cm/yr from historic offsets of man-made structures along the segment of the fault between Paicines and Cholame.