Ambient Noise Tomography Reveals Heterogeneous Structure of the Igneous Rocks in Hong Kong’s Upper Crust

Hong Kong, one of the most densely populated financial centers in the world, has received limited attention in subsurface structure imaging due to its tectonic quiescence. However, it sits atop the core of the Lianhuashan Fault Zone and was a center of multiple super volcanic eruptions during Yanshanian movement. The complex fault systems and widespread geothermal resources in adjacent region are legacies of these intense tectonic events. We deployed a temporary array of 13 portable seismic nodal sensors covering Hong Kong core area and recorded 21-day seismic data. Using ambient noise adjoint tomography, we imaged the upper 8 km of the crust at high resolution. Significant fault-controlled heterogeneity revealed indicates both geothermal potential and seismic hazard. A deep-seated fault beneath Lantau Island experienced intense fault dilation and volcanic activity as it served as a main magma conduit during Mesozoic. It left behind fractured felsic rocks (low velocity) and rigid mafic intrusions (high velocity), forming a potential seismogenic structure. Pronounced low-velocity anomaly beneath Tai Mo Shan may reflect geothermal activity. Combined with pervasive fracturing and abundant precipitation in Hong Kong, this suggests the presence of an uplift-driven convective geothermal system in the region.