Three-dimensional seismic imaging of the littoral fault zone in the Hong Kong region

The coastal South China is an extensional continental margin, and is also considered to be an intraplate region with low to moderate seismic activity levels. The evidence from some 600-700 years of Chinese historical earthquake records indicates that seismic activity levels appear to be significantly lower in the Pearl River Delta area, compared with the eastern and western coastal regions of South China. Almost all highly destructive earthquakes with magnitudes greater than 7.0 in historic times occurred along the east-northeast-trending littoral fault zone (LFZ) nearly parallel to coastline. It is therefore very important to obtain detailed subsurface seismotectonics in the coastal South China. In this presentation, we demonstrate how the fault zone has been successfully imaged by seismic tomography with a challenging experimental geometry. Based on the onshore-offshore seismic experiment near Hong Kong, the three-dimensional crustal structure in and around Hong Kong was imaged. We used both crustal refraction and reflection travel times from two offshore shot lines with a three-dimensional of land-based seismometer network. An iterative inversion algorithm was used to invert the data, and a series of checkerboard resolution tests were performed. The lateral resolution is assessed also by the Monte Carlo approach, and the individual velocity nodes down to mid-crustal levels (around 20 km deep) are well resolved. The application of this combination of model assessment methods have allowed us to validate the three-dimensional model given the challenging imaging conditions.