High-resolution seismic reflection surveying to delineate shallow subsurface geological structures in the karst area of Shenzhen, China

Near-surface seismic reflection surveys can produce high-resolution geological structural images for engineering and hydrological investigations. To help delineate shallow subsurface complex geological structures in a karst area and to better understand limestone cave formation, a high-resolution 2D seismic reflection profile was acquired and processed in the urban area of Shenzhen, China. The stacked images detail subsurface structures down to depths of 80–90 m, including a concave shaped reflection that curves upwards, two thrusts and one normal fault, as well as a hard rock basement reflection at the southern end of the profile which could not be mapped by borehole investigations due to the limited drilling depth. Our interpretations correlate well with borehole data and were supported by synthetic seismic modelling. Limestone caves are mainly found along faults and near rivers in this area. The results provide new insight on the formation mechanism and distribution of the karst caves. Movement along faults and erosion generated fractures and fissures in the limestone that provide channels for rainwater and groundwater to circulate. These waters, rich in carbonic acid, dissolve minerals in the limestone, resulting in the formation of underground cavities.