Three-dimensional Velocity Structure Beneath Guangzhou, China, Derived from Synchronous and Asynchronous Ambient Noise Tomography

Located at the northern margin of the Pearl River Delta, Guangzhou is characterized by complex subsurface structures resulting from the intersection of multiple active faults, leading to elevated geohazard risks. This study derives a high-resolution crustal shear-wave velocity structure by integrating data from two temporary seismic networks and local permanent stations using a joint ambient noise tomography approach that combines synchronous (C¹) and asynchronous (C²) cross-correlation techniques. The C¹ method extracts short-range ray paths between local stations, whereas the C² method constructs long-range paths across sub-arrays, significantly improving both path coverage and crossing density within the 1–8 s period band. Using multiple-filter analysis to extract Rayleigh wave dispersion curves, we employ a wavelet-based, sparsity-constrained direct inversion algorithm to construct a three-dimensional shear-wave velocity model down to 7 km depth. The results reveal pronounced spatial correlations between major faults—including the Guangzhou-Conghua (GCF), Shougouling (SF), Guangzhou-Sanshui (SSF), and Zhujiangkou (ZJF) faults—and distinct low-velocity anomalies, that reflect sedimentary basin structures controlled by fault activity. Furthermore, a prominent deep low-velocity anomaly beneath the GCF suggests an ongoing or past tectonic inversion process. This study demonstrates that the combined application of C¹ and C² ambient-noise tomography significantly enhances the imaging resolution of crustal structures in urban environments, providing crucial geophysical constraints for geohazard assessment and resource exploration in the Guangzhou region.