Characterization of the San Andreas Fault Paleoseismic Events at Wrightwood and Pitman Canyon

Report from previous SCEC support.
The Pl is currently funded by SCEC to complete 3 tasks related to paleoseismology on the southern San Andreas Fault: 1 ) collect and date 30 samples, mainly from the middle part of the stratigraphic section at Wrightwood (Figure 1, 2) to support undergraduates to convert a backlog of video and photologs of trenches into digital line data, and 3) to excavate two small connection trenches at Pitman Canyon (Figure 1) to clarify the stratigraphic relationships there.

For task 1, the samples indicated on Figure 2, plus 2 samples from an unknown section in a trench just SW of the edge of Figure 1 were collected and submitted for analysis at Beta Analytic and Lawrence Livermore (some were initially submitted to the USGS lab, and were pretreated there, but the lab was closed before they were analysed). Because most of the sample were submitted during the Fall only 2 are finished, but all are promised by the end of January. For task 2, undergraduates (under the supervision of the PI) have completed the line art for Trenches 14, 15, 16, 22 and 23, and are currently digitizing them. These trenches previously existed only as inked photographs, or photo or video records of portions of walls (generally simple areas; an example is shown in Figure 3) where all contacts and faults were flagged and labeled on the wall by the PI. This essentially completes our backlog of field data for the site. Finally, a small trench was excavated at Pitman Canyon, and in conjunction with C-14 dates funded by NEHRP, the entire Pitman Canyon site is now correlated and dated. Gordon Seitz, who is expected to complete his PhD on this site in the winter of 1998, will submit this work for publication within the next 6 months.