The FaultScan Long-Term Dense Nodal Array to Study the San Jacinto Fault (Southern California)

Abstract Large earthquakes involve processes that occur primarily at seismogenic depths of 5–10 km or more, which are difficult to observe in detail with traditional seismic networks. The FaultScan project established the first long-term, dense nodal array experiment by acquiring continuous data at 300 stations along the San Jacinto fault (Southern California) at the Piñon Flat Observatory for 2.5 yr (April 2022–October 2024). In this article, we report on the experiment logistics, data quality, and continuity, and on the instrumental issues. We further investigate some key features of the data as a basis for future studies. In particular, we describe the level of signal-to-noise enhancement by slant-stacking for the detection of small earthquakes along the San Jacinto fault. We also quantify how we can track local incoherent wind noise over the array and how it affects coherent signal stacking. Finally, we show an example of freight train noise cross-correlation between the FaultScan array and a permanent station across the fault as a tool for future studies focused on passive, noise-based seismic monitoring of the fault activity.