The confidence parameters in Table 5 and Figures 7-12 in Bakun and Wentworth (1997) were calculated using the site corrections for M/4) rather than Bakun and Wentworth's (1997) preferred relation M,(3). The conclusions of Bakun and Wentworth (1997) are not changed by these corrections. The corrected Table 5 and Figures are in this report and at http://quake, wr. usgs. gov/~bakun/.

No abstract

Five moderate (magnitude 6) earthquakes with similar features have occurred on the Parkfield section of the San Andreas fault in central California since 1857. The next moderate Parkfield earthquake is expected to occur before 1993. The Parkfield prediction experiment is designed to monitor the details of the final stages of the earthquake preparation process; observations and reports of seismicity and aseismic slip associated with the last moderate Parkfield earthquake in 1966 constitute much of the basis of the design of the experiment.

Main shocks of the earthquake sequences that occurred on the Parkfield section of the San Andreas fault in central California in 1922California in , 1934California in , and 1966 are characterized by southeast rupture expansion over the same 20-to 30-km-long section of the fault. Whereas the seismic moments for the 1922 and 1934 events are ideniical to within a precision of 10%, the seismic moment for 1966 is 20% greater than for the earlier events to within a precision of 20%. The Parkfield area seismicity, in general, seems well described by a recurring moderate size characteristic earthquake, repeating the same epicenter, magnitude, seismic moment, rupture area, and southeast direction of rupture expansion. An unexplained 10 year advance of the 1934 event is the only discrepancy in the hypothesis that the Parkfield earthquakes in 1857, 1881, 1901, 1922, 1934, and 1966 represent a strictly periodic process. Assuming the strictly periodic model and the absence since 1966 of the perturbations hypothesized for the 1922 to 1934 period, the next characteristic Parkfield earthquake should occur between 1983 and 1993. INTRODUCTION H. F. Reid's discussion of the mechanics of the 1906 California earthquake [Reid, 1910] contains the fundamental ideas underlying the time-predictable earthquake recurrence model: an earthquake occurs when strain accumulated since the preceding earthquake results in fault stress greater than the strength of fault material. Assuming a constant rate of strain accumulation and constant fault strength, Bufe et al. [1977] developed the time-predictable recurrence model to explain the recurrence of small earthquakes on a 9-km-long section of the Calaveras fault zone east of San Jose, California. Shimazaki and Nakata [ 1980] concluded that the recurrence of large thrust fault earthquakes at three sites of plate convergence around the Japan arcs was consistent with a time-predictable model rather than a slip-predictable model. That is, they concluded that the time interval between two successive large earthquakes is approximately proportional to the amount of coseismic displacement of the preceding earthquake and not of the following earthquake. Sykes and Quittmeyer [ 1981] have presented additional evidence in support for the time-predictable model for the recurrence of great earthquakes. Earthquakes on the Parkfield section of the San Andreas fault in 1857, 1881, 1901, 1922, 1934, and 1966 provide an excellent opportunity to test the applicability of recurrence models to regions characterized by recurring moderate-sized earthquakes. The similarity of intensity patterns [Sieh, 1978; Toppozada et al., 1981] and surface fractures along the San Andreas fault trace [Brown and Vedder, 1967] suggest that these shocks ruptured the same 20-to 30-km-long section of the fault (Figure 1). Lack of instrumental data precludes the determination of precise source parameters for the 1857, 1881, and 1901 shocks. In this paper we compare source parameters for of the fault since at least 1857 can be modeled, with t...