| The San Andreas Fault (SAF) offsets and deforms a remarkable sequence of late Holocene sediments and associated geomorphic features at Pitman Canyon, near San Bernardino, California. Extensive surface and subsurface investigations reveal paleoearthquakes and provide important insights into the accumulation and deformation of peat-bearing sections. The dated earthquakes allow the construction of fault behavior models for the SAF.;The exposed stratigraphic section is 9 meters thick, and contains more than 30 C-14 datable peat layers, of which 16 horizons are used to construct a chronology. We have discovered that laboratory C-14 pretreatments play a significant role, and based upon stratigraphicly consistent dates, we identify acid-only pretreatment as the most reliable. Peat-horizon and event dates were quantitatively refined by application of Bayesian statistical techniques, which use additional information including historical accounts, stratigraphic order, and time for peat accumulation to yield better constrained estimates. Regional peat-accumulation rates, based on 181 C-14 dates from three sites at different elevations provide compelling evidence for climatic control. This new finding allows the application of variable peat-accumulation rates as additional constraints for layer-date refinements.;Eight trench excavations, totaling 1600 square meters of exposures, contain evidence of at least 8 earthquakes of which the most recent 6 were recognized by consistent upward termination of faults, fissure fills, incremental folding, liquefaction, colluvial wedges, and a down-section increase in vertical and, likely, lateral separation. We introduce the paleoseismic index, a quantitative measure of paleoseismic event manifestation. A new unfolding method incorporating line-length balancing and limb-rotation measures was developed to extract event information. The best paleoearthquake age estimates are: 1812, 1680, 1480, 1400, 1330, and 1230 AD, which results in an average recurrence interval of 116 years for the closed intervals. A slip rate based on geomorphic offsets and the average recurrence interval is 30 +/- 9 mm/year.;Evidence for stratigraphic recording uncertainties at all SAF paleoseismic sites complicates evaluations of fault segmentation. However, correlation of all known events reveals no clear evidence for fault-rupture segmentation, as we infer that two out of six ruptures terminate between Pitman Canyon and Wrightwood, and three out of six terminate between Wrightwood and Pallett Creek.;This dissertation includes both my previously published and unpublished co-authored materials. |
