3D architecture and complex behavior along the simple central San Andreas fault

• Published in: Nature communications 2024-06, Vol.15 (1), p.5390-12, Article 5390
• Main Authors: Cheng, Yifang, Bürgmann, Roland, Allen, Richard M.
• Format: Article
• Language: English
• Subjects: 704/2151/2809; 704/2151/508; 704/2151/562; 704/4111; Creep rate; Earthquakes; Geological faults; Humanities and Social Sciences; Kinematics; Mechanical properties; multidisciplinary; Science; Science (multidisciplinary); Seismic activity; Seismicity; Spatial variations; Stress distribution
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-024-49454-z

The central San Andreas Fault (CSAF) exhibits a simple linear large-scale fault geometry, yet seismic and aseismic deformation features vary in a complex way along the fault. Here we investigate fault zone behaviors using geodetic observation, seismicity and microearthquake focal mechanisms. We employ an improved focal-mechanism characterization method using relative earthquake radiation patterns on 75,164 M l  ≥ 1 earthquakes along a 2-km-wide, 190-km-long segment of the CSAF, from 1984 to 2015. The data reveal the 3D fine-scale structure and interseismic kinematics of the CSAF. Our findings indicate that the first-order spatial variations in interseismic fault creep rate, creep direction, and the fault zone stress field can be explained by a simple fault coupling model. The inferred 3D mechanical properties of a mechanically weak and poorly coupled fault zone provide a unified understanding of the complex fine-scale kinematics, indicating distributed slip deficits facilitating small-to-moderate earthquakes, localized stress heterogeneities, and complex multi-scale ruptures along the fault. Through this detailed mapping, we aim to relate the fine-scale fault architecture to potential future faulting behavior along the CSAF. This study on the central San Andreas Fault shows how its fine-scale structures and kinematics, resolved using high-quality focal mechanisms of small earthquakes, are influenced by a weak, poorly coupled fault zone.