Linear Array Double Difference Adjoint Ambient Noise Tomography of the Central Tanlu Fault Zone, Eastern China

Abstract

In response to the need for high‐resolution imaging of shallow crustal structure, we present a linear array double‐difference (DD) adjoint tomography method, using DD Rayleigh wave traveltime measurements for enhanced spatial resolution. This method, validated through synthetic experiments, improves velocity anomaly detection with fewer iterations compared to absolute traveltime measurements. Applied to data from four linear seismic arrays in the central Tanlu fault zone (TLFZ) in the eastern China, our approach integrated both DD and absolute difference (AD) of adjoint traveltime measurements. We performed cluster analysis for data quality control, reducing data outliers and increasing reliability, particularly in suppressing cycle skipping for short‐period measurements. The resulting high‐resolution S‐wave velocity profiles in the shallow crust well delineate geological structures, revealing a continuous low‐velocity anomaly beneath the eastern branch of TLFZ. Our comparative analysis with the southern segment of TLFZ further highlights the segmented nature of the fault zone structure. These variations might suggest a dominant influence of deep magmatic processes due to destruction of the North China Craton. Our study links shallow structural features to deeper geodynamic activities, emphasizing the role of TLFZ as a critical tectonic boundary.