Characteristics and Formation of Dongguan Basin, China: Insights from Shallow Crustal Shear Velocity Structure Using Dense Seismic Array

Abstract

The Dongguan basin (DGB) is located at the southeastern edge of the South China block, within a tectonic transition zone along the northern continental margin of the South China Sea. It lies near several active faults that have the potential to generate earthquakes. As part of the Greater Bay Area, the basin hosts densely populated urban regions where site effects could significantly amplify ground shaking during future earthquakes. In this study, we apply two ambient noise-based methodologies—the double-beamforming (DBF) and horizontal-to-vertical spectral ratio (HVSR) methods—to investigate the shallow crustal structure of the Dongguan basin. The system of faults that bound the basin is clearly delineated by the velocity anomalies observed in our 3D VS model derived from Rayleigh-wave dispersion curves, with major velocity boundaries coinciding with the Shilong–Houjie fault, Huangqifeng fault, and Xinhui–Shiqiao fault. Pronounced low-velocity anomalies are identified near the intersections of these faults, suggesting zones of structural complexity and possible fluid activity. The VS model further reveals that bedrock is deeper in the eastern basin and shallower in the west. In contrast, the HVSR analysis shows that Quaternary sediments are thicker in the west and thinner in the east, indicating an inverse relationship to bedrock depth. This opposite pattern likely reflects early differential crustal extension during basin formation, followed by sediment accumulation in the western section driven by transport from the Pearl River. Our results provide new constraints on the geometry of the DGB and its fault systems. The fault intersections may serve as conduits for geothermal fluids, and site effects in the western part of the basin may pose a higher seismic hazard compared with the east.