Unraveling the Temporal Dynamics of Channel Incision in the Carrizo Plain: Implications for Seismic Hazard Assessment
Sinan O. Akciz, & Nathan D. BrownSubmitted September 7, 2025, SCEC Contribution #14854, 2025 SCEC Annual Meeting Poster #TBD
New high-resolution topographic data sets make geomorphic methods increasingly attractive for hazard analysis globally. Plots that show the distribution of displaced geomorphological features along the strike of a fault are commonly used to infer the slip distribution during previous earthquakes and even the magnitudes and recurrence of large surface-rupturing earthquakes by utilizing slip rate information. The fundamental premise of these interpretations is that channel formation and incision occur at an average decadal frequency, which significantly exceeds the recurrence interval of earthquakes along the displacing faults. The investigation aims to validate assumptions about channel formation frequency compared to earthquake recurrence along the San Andreas Fault System. Previous studies, such as those by Grant Ludwig et al. (2010), have attempted to correlate radiocarbon ages from channel fills with regional flooding events, emphasizing the need for local paleoclimate datasets and precise age constraints for accurate slip data interpretation. Our study explores the incision ages of two offset channels (Sieh32 and Sieh33) in the Carrizo Plain, California, by applying the pIR/IRSL dating method to K-feldspar grains from their fill deposits. These channels, offset by approximately 16 m and 10 m, respectively, exhibit varied earthquake histories. Our results, combined with paleoclimate records from the Santa Barbara Basin and a local sag pond at the southern end of the Carrizo Plain, indicate incision events at 770 CE, 1260 CE, and 1760 CE, contrasting with previous assumptions based on radiocarbon dating. Our findings propose a quasi-periodic occurrence of incision events every 500 years, exceeding the earthquake recurrence intervals of 45-145 years for at least the last 1000 years. This research contributes to understanding the geomorphic evolution of the Carrizo Plain, highlighting the influence of supraregional climatic changes on sedimentation and channel morphology. Additionally, it underscores the importance of integrating paleoclimate and paleoseismic data to refine earthquake hazard assessments and improve slip-per-event estimates along the San Andreas Fault. The multidisciplinary approach promises to enhance future seismic and climatic studies, offering valuable insights into California's dynamic landscape.
Key Words
San Andreas Fault, Carrizo Plain, paleoseismology, variable slip
Citation
Akciz, S. O., & Brown, N. D. (2025, 09). Unraveling the Temporal Dynamics of Channel Incision in the Carrizo Plain: Implications for Seismic Hazard Assessment. Poster Presentation at 2025 SCEC Annual Meeting.
Related Projects & Working Groups
Earthquake Geology