Evidence for Active Faults as Hydraulic Barriers to Cross-Fault Flow: A case study of the Earthquake Valley Fault in Warner Basin, southern California

Matthew Weingarten, & Jennasea Fisher

Submitted September 8, 2024, SCEC Contribution #13987, 2024 SCEC Annual Meeting Poster #109

Fluid flow along active faults can play a crucial role in fault behavior as fault permeability exhibits a strong control on stress accommodation at depth. Broadly speaking, the spatial distribution of fault hydraulic properties within the southern San Andreas Fault system, encompassing the San Andreas Fault (SAF), the San Jacinto Fault (SJF) and Elsinore Fault (EF), are constrained poorly. Here, we aim to investigate the hydrogeologic properties of the Earthquake Valley Fault (EVF) in Warner Basin, California, which lies between the Elsinore and San Jacinto Faults in southern California. Recent paleoseismic work indicates a most recent earthquake on the EVF of ~Mw6.3 circa 1890(Ackiz & Rockwell, 2022). Within our study area, two strands of the EVF, the Agua Tibia South and North faults, are NW-SE trending, subvertical, right-lateral strike slip faults constrained from well logs and prior surficial geologic investigations. Preliminary analysis of long-term groundwater pumping and monitoring well data within Warner Basin reveal a complex fluid flow landscape. We hypothesize the EVF in Warner Basin act as barriers to flow, resulting in observable differences in groundwater response to pumping from one fault compartment to another. Time-series analysis show that the Agua Tibia South Fault, in particular, exhibits strong barrier-like behavior, compartmentalizing the upstream and downstream portions of the watershed. Hydraulic conductivity estimates range over two orders of magnitude with lower conductivity values estimated on the northern side of the Agua Tibia South Fault and higher values estimated south of the fault. These findings show promise in the use of long-term, near-field groundwater pumping and monitoring well data to explore active fault zone hydrogeologic structure.

Key Words
fault zone structure; fault zone anisotropy; fault zone permeability; groundwater; active faults

Citation
Weingarten, M., & Fisher, J. (2024, 09). Evidence for Active Faults as Hydraulic Barriers to Cross-Fault Flow: A case study of the Earthquake Valley Fault in Warner Basin, southern California. Poster Presentation at 2024 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology