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Three-Dimensional Visualization and Implications for Reconstruction of the Chalk Hill Paleoseismic Site on the Rodgers Creek Fault Near Windsor, California

Description: 

The Rodgers Creek fault is a primary strand of the northern San Andreas fault system, yet investigations of its recent slip history are limited and are mostly absent north of the city of Santa Rosa. Here we report results from a site located east of the town of Windsor at the Chalk Hill Winery, where we use 3-dimensional site reconstruction to integrate the results of multiple trenches across the main trace of the Rodgers Creek fault with ambiguous results from geomorphic analysis.
At the site, an upstream-facing scarp and dextrally-offset landform appear to displace an abandoned channel of Windsor Creek by ~150 m. In detail, however, the channel margins and terrace risers used for reconstruction are inconsistent and leave significant ambiguity in site reconstructions for offset measurements. Three trenches excavated perpendicular to the scarp, spaced at ~10 m intervals, show a juxtaposition of laterally variable Holocene alluvial fill deposits against Plio-Pleistocene gravels. Within each trench, multiple fault strands display locally complex deformation histories with no clear earthquake horizons. At least one strand extends through agriculturally modified deposits and is visible in the modern surface, suggesting that it may accommodate ongoing creep, consistent with prior InSAR analysis on the northern Rodgers Creek fault.
We use a virtual 3-dimensional site reconstruction to interpolate and project fault and stratigraphic surfaces between the trenches. This approach allows us to develop a coherent spatio-temporal understanding of site evolution, which helps illuminate the relationship between fault strands and elucidates potential displacement reconstructions at the site. We find that the 3D reconstruction also highlights the inherent assumptions required for site reconstruction and, in turn, provides a visual intuitive test of our assumptions and interpretations and their implications for deformation history at the site.

Session: From Earthquakes to Plate Boundaries: Insights Into Fault Behavior Spanning Seconds to Millennia [Poster]

Type: Poster

Date: 4/20/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Charles Trexler

Student Presenter: No

Invited Presentation: 

Authors