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

摘要： 综合探查表明,福州盆地的主要断层均无全新世活动。通过区域地壳动力学与地震构造背景分析、地震活动水平统计对比等,综合判定了福州盆地的地震环境及主要断层潜在地震的最大震级。结果表明:福州盆地位于台湾动力触角对大陆作用的弱影响区,但靠近强、弱影响区的过渡边界,处于有、无≥6级强震区的过渡地带。与福建—粤东北沿海发生过强震的地段相比,福州盆地及附近主要断裂的最晚活动时代偏老,壳内的低速层不显著。另外,在福建及邻区的12个地震构造单元中,福州盆地单元的地震活动水平最低。该盆地西缘和南缘的闽候-南屿断层和五虎山北麓断层是具有发生中等地震潜势的相对危险断层段,潜在地震的最大震级估值为M_S6.0和5.6。

关键词: 地震环境, 相对危险断层段, 潜在最大震级, 福州盆地