Holocene activity of the San Andreas fault at Wallace Creek, California

Abstract

Wallace Creek is an ephemeral stream in central California, the present channel of which displays an offset of 128 m along the San Andreas fault. Geological investigations have elucidated the relatively simple evolution of this channel and related landforms and deposits. This history requires that the average rate of slip along the San Andreas fault has been 33.9 ± 2.9 mm/yr for the past 3,700 yr and 35.8 + 5.4/-4.1 mm/yr for the past 13,250 yr. Small gullies near Wallace Creek record evidence for the amount of dextral slip during the past three great earthquakes. Slip during these great earthquakes ranged from-9.5 to 12.3 m. Using these values and the average rate of slip during the late Holocene, we estimate that the period of dormancy preceding each of the past 3 great earthquakes was between 240 and 450 yr. This is in marked contrast to the shorter intervals (-150 yr) documented at sites 100 to 300 km to the southeast. These lengthy intervals suggest that a major portion of the San Andreas fault represented by the Wallace Creek site will not generate a great earthquake for at least another 100 yr. The slip rate determined at Wallace Creek enables us to argue, however, that rupture of a 90-km-long segment northwest of Wallace Creek, which sustained as much as 3.5 m of slip in 1857, is likely to generate a major earthquake by the turn of the century. In addition, we note that the long-term rates of slip at Wallace Creek are indistinguishable from maximum fault-slip rates estimated from geodetic data along the creeping segment of the fault farther north. These historical rates of slip along the creeping reach thus do represent the long-term-that is, millennial-average, and no appreciable elastic strain is accumulating there. *Deceased. Finally, we note that the Wallace Creek slip rate is appreciably lower than the average rate of slip (56 mm/yr) between the Pacific and North American plates determined for the interval of the past 3 m.y. The discrepancy is due principally to slippage along faults other than the San Andreas, but a slightly lower rate of plate motion during the Holocene epoch cannot be ruled out.

Segmentation of the northern San Jacinto Fault Zone, southern California

“…As noted by Jones [1988], the strain field changes from strike slip to normal across the branch region. Also the branch region is a discontinuity in slip rate in the San Andreas fault zone; northwest of the branch region the San Andreas fault zone is the primary plate boundary, and displacement across it occurs at about 34 mm/yr [Sieh and Jahns, 1984]; southeast of the branch region displacement across the San Andreas fault zone occurs at about 25 mm/yr [Weldon and Sieh, 1985]. Thus strain accumulates on the San Andreas fault at different rates on either side of the branch.…”

Evaluation of hypotheses for right-lateral displacement of Neogene strata along the San Andreas Fault between Parkfield and Maricopa, California

“…Using the estimate of right-lateral displacement of 254 ± 5 km proposed by Huffman (1972), we calculate an average slip rate of about 28.2 millimeters per year (mm/yr) with a possible range of 24.9-32.4 mm/yr. Our estimated long-term rates are similar to (a) an implied long-term slip rate of about 30 mm/yr from San Andreas Fault studies in central and northern California that indicate 165 km of right-lateral displacement since 5.5 Ma (Graymer and others, 2013); (b) estimated slip rates of 33.9 ± 2.9 mm/yr for the past 3,700 years based on geological investigations along the San Andreas Fault (Sieh and Jahns, 1984); (c) estimated slip rates of 29.3-35.6 mm/yr from studies of fault trenches in the Carrizo plain (Noriega and others, 2006); (d) geodetic slip rates of 32.2-38.7 mm/yr along the 5 It should be noted that Ross (1979Ross ( , 1980Ross ( , 1984 reported some differences between conglomerate clasts in the Santa Margarita Formation and basement rocks found by him in the Gabilan Range, but Ryder and Thomson (1989, p. 47) attributed these differences to inadequate exposures in the Gabilan Range.…”

Space- and Time-Dependent Probabilities for Earthquake Fault Systems from Numerical Simulations: Feasibility Study and First Results

“…Their work suggested that recent ruptures of the SAF in the Carrizo were clustered in time (''uncharacteristic earthquakes'') rather than more regularly spaced in time (''characteristic earthquakes''). So while the long-term average recurrence time might be several centuries (SIEH and JAHNS, 1984;WGCEP 1988 and1995), their data showed evidence for as many as The results shown in Fig. 2b suggest that the next major M [ 7.0 earthquake could occur on the Carrizo reach of the SAF, possibly within thirty years from 2009.…”