长乐-诏安断裂带东支东山段晚更新世活动的年代学证据及其意义

Chronological evidence and significance of Late Pleistocene activity in the Dongshan segment of the eastern branch of the Changle-Zhao′an fault belt

长乐-诏安断裂带是福建沿海的主要活动断裂之一,沿断裂带曾发生多次破坏性地震,是福建省陆域上的主要发震构造。中国东部地区破坏性地震的发生与晚更新世活动断裂有密切联系,因此研究长乐-诏安断裂带在晚更新世的活动具有重要意义。在对福建省东山县最新发现的长乐-诏安断裂东支东山段剖面的野外详细调查的基础上,通过对断层下盘地层和断层上断点以上地层中钾长石光释光测年,确定了长乐-诏安断裂带东支东山段的具体活动时间在(34.8±8.3)~(48.0±3.5)ka之间,显示该断裂至晚更新世晚期仍有活动,属晚更新世活动断裂;通过震级(M)与地震断层位错量(D)经验关系拟合法估算,该断裂的最大发震能力为6.5~7.0级地震。该晚更新世活动断裂的确定和最大震级估算,为长乐-诏安断裂带的活动性提供了确切年代学证据,为东山县地区城市安全评价提供了依据。

[Objective]The Changle-Zhao′an fault zone is one of the primary active faults running along the coast of the Fujian Province.This fault zone has induced several destructive earthquakes and is thus a principal seismogenic structure in the Fujian Province.Therefore,tight constraints on the Late Quaternary activity of the Changle-Zhao′an fault zone has significant significance.[Methods]Based on field survey along the Dongshan segment of the eastern branch of the Changle-Zhao′an fault in the Dongshan County,Fujian Province,the timing for the motion of this fault portion was determined to be between(34.8±8.3)ka and(48.0±3.5)ka by using K-feldspar luminescence dating of the strata above the fault break point and footwall.[Results]This indicates that the fault remained active since the Late Pleistocene.Furthermore,we estimated the potential maximum seismicity along the fault using the empirical relationship between magnitude(M)and fault dislocation(D).[Conclusion]Determination of a Late Pleistocene active fault,along with the estimate of the maximum earthquake magnitude,provides precise chronological evidence for understanding the activity of the Changle-Zhao′an fault zone.Our results thus serves as an important basis for conducting urban safety assessments in Dongshan County.