关键词: 地震环境, 相对危险断层段, 潜在最大震级, 福州盆地

Abstract: Comprehensive prospecting in Fuzhou basin has revealed that all the main faults in the basin have not been active since Holocene time. Therefore, how to assess the long-term seismic risk of such a type of fault has become an important problem. Taking the Fuzhou basin as an example, we seek after a possible way to evaluate the long-term seismic risk on non-Holocene active faults in eastern China. Firstly this paper demonstrates the position of the Fuzhou basin in the regional earthquake environment by analyzing regional crustal dynamics and seismic background, and then finds out the fault-segments of relatively high seismic risk and estimate the maximum magnitude of potential earthquakes on these fault-segments through the comparison of seismotectonic conditions and the statistic analysis of seismic activity levels in individual seismotectonic zones. The main results are as follows: The Fuzhou basin lies in the area that has been influenced slightly by the action of the Taiwan Dynamic Wedge (TDW), but is close to the border between the areas that are slightly and strongly influenced by the TDW, and is located at the transition zone between regions with and without strong earthquake (of M_S≥6.0) occurrence. As compared with the seismotectonic background in Fujian northeast Guangdong areas, where strong earthquakes have occurred, the main faults in Fuzhou basin and its neighboring area have older ages of the latest activities, while the crust beneath the region contains less distinct low-velocity layers. Moreover, among 12 zones that are taken as statistic units for seismicity in Fujian, northeastern Guandong and the border region among Fujian, Guangdong and Jiangxi Provinces, the unit in Fuzhou basin shows the lowest level of seismicity. It is suggested that the Minhou-Nanyu Fault along the western border of the Fuzhou basin and the Wuhushan northern-foot fault along the southern border of the basin are the two fault-segments with relatively high potential of moderate to strong earthquakes. The maximum magnitudes of the potential earthquakes on the two fault segments have been estimated to be M_S6.0 and 5.6, respectively, on the basis of the worldwide empirical relationship between subsurface rupture scale and magnitude of earthquake.

Key words: earthquake environment, fault-segment with relatively high seismic risk, potential maximum magnitude, Fuzhou basin