Project title exploratory paleoseismic investigation of the quin sabe fault, SAN benito county, californiaperiod of performance 4 1 2023 through 3 31 2024AWARD purpose the quin sabe fault is one of…

Project title exploratory paleoseismic investigation of the quin sabe fault, SAN benito county, californiaperiod of performance 4 1 2023 through 3 31 2024AWARD purpose the quin sabe fault is one of several poorly characterized structures that is closely associated with the SAN andreas fault (SAF) and calaveras fault (CF) junction located along the rapidly urbanizing state HWY 152 corridor. The QSF is included in the existing state wide seismic source model (uniform california earthquake rupture forecast UCERF3 field ET AL., 2013), and the underlying statewide community fault model (SCFM) that uses poorly constrained information on the QSF. For example, these models use a slip rate of 0.2 to 1 MM YR, despite limited information on the recency, timing, and recurrence of earthquakes for the QSF, and little to no available geologic slip rate information (dawson and weldon, 2013). Further, this slip rate is an estimate derived from vertical displacement of late quaternary alluvial deposits, despite abundant evidence of dominant right lateral strike slip motion for the QSF. This proposed research aims to refined these underlying parameters for the QSF, and if successful, these results could provide the first information on the late quaternary paleoseismic history of earthquakes for the QSF, including potential event timing and valuable fault characterization data for input to UCERF3 and future california statewide fault models. This research builds on initial pilot work, also funded by the USGS EHP program (award G21AP10015 bloszies and baldwin, 2022), that performed quaternary geologic and geomorphic mapping of the QSF and (1) refined the location of multiple potential holocene active fault strands, (2) identified multiple potential paleoseismic sites, and (3) provided key information on the potential structural connection between the SAF and CF. To achieve the stated goals of this study, one to two fault normal trenches will be excavated at the samarkand ranch site, a paleoseismic site highly ranked by bloszies and baldwin (2022). This location exhibits prominent tectonic geomorphology associated with the QSF and holocene sedimentation that will likely aid in recording fault activity and event timing information. The geologic data collected from trenches will help inform probabilistic seismic hazard models (e.g. ucerf) that incorporate the QSF, and which rely on earthquake timing and slip rate data. Currently, there is no information on the most basic needs of earthquake forecasting for the QSF, such as holocene activity and age of the most recent event (MRE) information that is important to addressing the role of the QSF in the CF and SAF junction. Activities to be performed 1. Perform limited, site specific geologic mapping to best locate paleoseismic trenches.2. Excavate two trenches and interpret exposed sediments, sampling for age analyses where possible.3. Review trench interpretations with subject matter experts.4. Submit samples for lab analysis while simultaneously compiling findings from field effort.5. Prepare final technical report (FTR), prepare data deliverables, and disseminate findings.deliverables and expected outcomes deliverables will include data generated from trench exposures, including photomosaics, graphical logs, maps, and results of geochronological analysis. All deliverables will be included in the FTR. Intended beneficiaries data derived from these investigations should be useful to researchers in the fields of seismic hazard assessment and paleoseismology within the sfba.subrecipient activities N a