General Seismic Architecture of the Southern San Andreas Fault Zone around the Thousand Palms Oasis from a Large-N Nodal Array

Abstract

We discuss general structural features of the Banning and Mission Creek strands (BF and MCF) of the southern San Andreas fault (SSAF) in the Coachella Valley, based on ambient noise and earthquake wavefields recorded by a seismic array with >300 nodes. Earthquake P arrivals show rapid changes in waveform characteristics over 20–40 m zones that coincide with the surface BF and MCF. These variations indicate that the BF and MCF are high-impedance contrast interfaces—an observation supported by the presence of seismic reflections. Another prominent but more diffuse change in SSAF structure is found ∼1 km northeast of the BF. This feature has average-to-low arrival times (P and S) and ambient noise levels (at <30 Hz), and likely represents a relatively fast velocity block sandwiched between broader MCF and BF zones. The maximal arrival delays (P ∼0.1 s and S ∼0.25 s) and the highest ambient noise levels (>2 times median) are consistently observed southwest of the BF—a combined effect of Coachella Valley sediments and rock damage on that side. Immediately northeast of the MCF, large S minus P delays suggest a broad high VP/VS zone associated with asymmetric rock damage across the SSAF. This general overview shows the BF and MCF as mature but distinctly different fault zones. Future analyses will further clarify these and other SSAF features in greater detail.

Structural properties of the Southern San Andreas fault zone in northern Coachella Valley from magnetotelluric imaging

“…Anomaly C1 represents the broad SSAF zone 308 (~3 km wide at the surface) in the upper crust. This near-surface width is corroborated by 309 the present of several anomalous fault damage-related structures within that same ~3 km-310 wide zone as revealed by analysis of large-N seismic array data (Share et al 2022) zone in the ductile crust that helps drive local earthquake activity in the more resistive and 334 mechanically stronger crust above it. This correlation between smaller scale brittle failure 335 and high resistivity has been observed along minor faults in central California (Bedrosian 336 et al 2004) and in Turkey (Gurer & Bayrak 2007).…”

Active Dipping Interface of the Southern San Andreas Fault Revealed by Space Geodetic and Seismic Imaging

“…Additional details about the array deployment may be found in Share, Qiu, et al. (2022). The location of the array deployment is roughly coincident with Line 5 (stations 502790–503240) from the Salton Sea Imaging Project (SSIP) (Rose et al., 2013), where larger‐aperture arrays for seismic reflection and potential‐field modeling have been deployed (Fuis et al., 2017; Persaud et al., 2016; Share, Peacock, et al., 2022).…”

Lateral Variations Across the Southern San Andreas Fault Zone Revealed From Analysis of Traffic Signals at a Dense Seismic Array

“…In the present study, we use seismic data recorded by a dense temporary nodal array across the BF and MCF near the Thousand Palms Oasis Preserve in the Coachella Valley (Figure 1) to image the subsurface properties of the SSAF in the area. During the ∼1 month deployment, only a small number of local earthquakes occurred near the array (Share et al., 2022), necessitating the use of other signals for detailed seismic imaging. Among such signals, seismic waves generated by cars and trains are used increasingly in imaging and monitoring studies due to their high reproducibility and simple source features (Fuchs et al., 2017; Jiang et al., 2022; Meng et al., 2021; Pinzon‐Rincon et al., 2021; Rezaeifar et al., 2023).…”