Multidisciplinary investigation of determining channel incision ages in the Carrizo Plain, California.

Sinan O. Akciz, & Matthew Kirby

Published August 16, 2021, SCEC Contribution #11522, 2021 SCEC Annual Meeting Poster #090

Offset channels are routinely used to determine slip rates and slip-per-earthquake measurements. Plots showing the distribution of slip along the strike of a fault are used to infer the slip distribution during previous earthquakes and even magnitudes and recurrence of large surface rupturing earthquakes. Along the faults that collectively form the San Andreas Fault (SAF) System, the underlying assumption for such interpretations is that channels form and incise on an average decadal frequency which is much more rapid than the earthquake recurrence along these faults. Grant et al. (2010) tried to validate this assumption by comparing limited radiocarbon age determinations from the fills of two channels in the Carrizo Plain to major flooding events interpreted from the sedimentary cores retrieved from the Santa Barbara Basin. We collected five, 2-m sediment cores for this project to conduct a detailed study of sedimentary cores from a sag pond along the SAF to extract the fine details of local spatiotemporal climatic variability within the last 1000 years in the Carrizo Plain. To date, CLPC21-4 has been opened, described, and analyzed for magnetic susceptibility, total organic matter, total carbonate, and charcoal at 1 cm contiguous intervals. A second core, CLPC21-3, has also been opened, described, and analyzed for magnetic susceptibility. Both cores contain evidence for flood events as well as deeper lake conditions and modern playa conditions. Key to this project is the dating of the flood events (i.e., the potential channel forming events) and the deep lake/playa intervals. At present, we speculate that these cores capture the past 1000-2000 years, including the Little Ice Age and the Medieval Climatic Anomaly. We are also using Pb210 and Cs137 to date the most recent 200 years - a period when radiocarbon dating is less accurate. This paleoclimate investigation will provide an independent constraint to incision ages for offset channels in the Carrizo Plain. In addition, the paleoclimate record will be a locally determined, independent dataset for the assessment of the completeness of paleoseismic earthquake evidence records along the SAF in the Carrizo Plain.

Key Words
San Andreas Fault, paleoclimate

Citation
Akciz, S. O., & Kirby, M. (2021, 08). Multidisciplinary investigation of determining channel incision ages in the Carrizo Plain, California.. Poster Presentation at 2021 SCEC Annual Meeting.

Related Projects & Working Groups
San Andreas Fault System (SAFS)