Imaging Shallow Complex Vs Structure Using F–J Surface-Wave Tomography with Partition Similarity Test: A Case Study at the San Jacinto Fault Zone

Dense seismometer arrays offer new opportunities for refining the exploration of near-surface near-fault structures. By deploying regional dense seismic arrays, seismologists have significantly advanced their insights into structures, rupture processes, and dynamic behaviors for fault systems. However, achieving high-resolution shear-wave velocity structures remains challenging. This study applies the frequency–Bessel transform (F-J) method, a multimodal surface-wave tomography technique, to image complex subsurface systems. The F-J method enables broad frequency band dispersion curves, overtone extraction, and improved resolution. To address challenges in reliable subarray selection for 3D complex subsurface imaging when using this array-based method, we introduce a partition similarity test to quantitatively and adaptively generate suitable subarrays. We apply this method to image the Sagebrush flat site along the Clark fault branches of the San Jacinto fault zone, demonstrating its effectiveness in mitigating the branched dispersion phenomenon that appears in the traditional workflow of the F-J method. The high-resolution imaging results reveal two low-velocity anomalies, a trapping structure, an inferred fault, and significant lateral velocity variations along the Clark fault branches.