珠江三角州沙湾断裂带第四纪活动性研究

Quaternary activity of Shawan fault in Pearl River delta

沙湾断裂是珠江三角州北西向的主干断裂。为了查清其第四纪活动性,我们进行了1∶5万地质地貌填图、断层活动年代测定、氡气测量、浅层地震勘测和联合钻孔验证及构造解析等工作。第四纪地貌与断裂的耦合性及历史地震情况说明,沙湾断裂目前仍有一定活动性;地质调查及勘测未发现断裂切割第四系,氡气测量结果表明断裂目前活动性中等以下,说明沙湾断裂目前活动性较弱;年代测量结果表明断裂在中更新世中期至晚更新世前期活动性较强,晚更新世以后活动性渐弱,仅在南段南沙区大岗镇罗汉山发现晚于100 ka剖面。罗汉山构造解析实例说明三角洲局部地段仍受断裂活动控制处于拉张环境,但全新世以来活动性渐弱。综合研究认为,沙湾断裂目前仍有一定活动性,但活动性较弱。

The Shawan fault is one of the most important faults in Pearl River delta. To explain the Quaternary activity of Shawanfault, the authors conducted a series of work, such as 1：50000 geological mapping, chronological study, determination of radon,shallow seismic reflection and combined drilling verification. According to the analysis of Quaternary geomorphology and fracturecoupling as well as the characteristics of historical seismic reflection, the fault is still active. Field survey and shallow seismicreflection show that the fault didn’t cut Quaternary strata, and radon measurement also shows that the intensity of the fault activityis weak; ESR chronology shows that the activity intensity was relatively strong before late Pleistocene, and afterward it becameweak; tectonic analysis of Luohanshan indicates that local area of Luohanshan was in a tension environment, but activity intensityhas become weaker and weaker since late Holocene. In short, Shawan fault is still active, but the intensity is weak.