Passive and active source imaging of the deep structure in the Pearl River Delta using a dense nodal array

The methods of deep seismic sounding (DSS) and dense nodal array (DNA) are based on the same observation systems and instruments. DSS offers advantages in constructing velocity models of the crust and upper mantle, whereas DNA is used to build crustal geometric models. Combining DSS and DNA can effectively enhance the deep earth exploration techniques. This study provides an example of such integration. We applied the teleseismic receiver function imaging method to the continuously recorded data from the DSS profile L1 and constructed a crustal geometric structure model for the Pearl River Delta. The study revealed the following characteristics of the crustal structure and fault zone: (1) the crustal thickness is 28–30 km, thinning gradually southeast of the Wuchuan-Sihui fault; (2) the average crustal VP/VS is ~1.73 near the Wuchuan-Sihui fault, but < 1.70 in other segments; and (3) a low-velocity zone exists in the upper to middle crust, horizontally separated by the Enping-Kaiping fault zone. These results suggest that the crust of the Pearl River Delta region has undergone significant thinning. The low average crustal VP/VS and lower crustal VP indicate that this is mainly caused by the lower crust thinning. We propose that the Wuchuan-Sihui and Enping-Kaiping faults dip eastward into the deep crust and may penetrate the Moho. The formation and evolution of these faults are controlled by thermal uplift and the southeastern extension of the lithospheric mantle. Joint exploration using DSS and DNA provides multi-parameter and multi-scale constraints on the crust and upper mantle structures, offering significant insights into the interface properties, fault extension, and melt flow distribution. The combined DSS and DNA techniques has broad applications in deep structural probing and mineral resource exploration.