Tomographic evidence for a link between historical seismicity and anomalous crustal structures in the Hong Kong region

In terms of the general level of seismicity, the region in the vicinity of Hong Kong has been relatively quiet. The region is not generally perceived to be an earthquake-prone area despite the fact that some of the intraplate earthquakes along the coastal fault zone were significantly destructive and had magnitudes > 6.0. In order to improve our understanding of the regional tectonics, it is important to understand the relationship between the crustal structure and seismicity in this 400+ km long fault zone along the South China coast. However, very few empirical constraints on the crustal structure of this coastal area have hitherto been available. We here present the first three-dimensional seismic tomographic model of the crust in the Hong Kong region for studying the relationship between the seismicity pattern and crustal structure in coastal South China. We characterize the well-resolved crustal anomalies identified in our tomographic model and study them by taking into account i) the characteristics of recorded earthquakes; ii) results from earthquake simulations; and iii) the surface tectonics. The main result of our study is that there exists a high spatial correlation between the along-strike subsurface heterogeneities of the fault zone around 30 km south of Hong Kong and the seismicity pattern of the area. In this presentation, we will also discuss the implications of our results for intraplate earthquakes and the regional tectonics of coastal South China. Our results thus provide new empirical constraints for reevaluating the arguably underestimated seismic risks in this densely populated region.