Abstract
The structural geometry and kinematic evolution of the San Andreas Fault System (SAFS) remain fundamental topics in continental strike-slip tectonics, directly governing seismic rupture dynamics and regional hazard assessments. While surface traces and deep seismicity have been extensively cataloged, the intricate three-dimensional architecture of the upper crust across critical transpressional segments has historically suffered from sparse subsurface imaging. In this study, we present a structural analysis of a high-resolution, deep-penetrating 3D seismic reflection volume spanning an exceptionally complex, transpressional transition zone within the southern-central SAFS. Post-stack and pre-stack depth migrations, calibrated with deep exploratory well logs, resolve structural geometries down to depths exceeding 6 km with decameter-scale vertical resolution. Our interpretations reveal an asymmetric positive flower structure characterized by a steeply southwest-dipping master strike-slip fault (78°–84°) that bifurcates upward into synthetic Riedel shears, outward-verging thrust splays, and associated en echelon fault-propagation folds. Quantitative displacement analysis across syn-tectonic Pliocene–Quaternary strata indicates clear kinematic strain partitioning, wherein oblique plate convergence is decoupled into nearly pure strike-slip displacement along the primary sub-vertical fault plane and localized orthogonal shortening accommodated by flanking low-angle reverse faults. These findings challenge planar vertical models commonly applied in kinematic rupture simulations and offer critical structural constraints for evaluating earthquake hazard potential and strain distribution along complex transform boundaries.
