The characteristics of Quaternary activity of faults in the sea area near the Yangtze River mouth

By shallow seismic prospecting, it is showed that the faults in the sea area near the Yangtze River mouth are mainly the NE and NW-trending faults. The main activity time of fault is Pliocene to Early Pleistocene, and the latest activity is up to Middle Pleistocene. The maximum of fault is generally several tens meters with the throw decreased upward. The dislocation near the bottom of Middle Pleistocene is 12~13 m. The average vertical dis-placement rate is on a level of 10-3 mm/a.

Preliminary Study on Cenozoic Group and Fault Activity in the Sea Area Near the Yangtze River Mouth

By shallow seismic prospecting, the Cenozoic Group in the sea area near the Yangtze River Mouth can be divided into five seismic sequences. They correspond to the Quaternary, Pliocene, Upper Miocene, Lower Miocene and Eocene respectively. The Quaternary System covers all the detecting area. The Tertiary System overlaps and thins out from NE to SW. The sedimentary basement mainly consists of volcanic rock (J 3) and acidic rock (r 3 5). Paleogene or Late Cretaceous basins are not found there. The faults that have been detected are all normal faults. They can be divided into three groups (NE, NW, near EW) by their trend. The NE and NW trending faults are predominant, and agree with aeromagnetic anomaly. Their length and displacement are larger than that of the EW trending faults. The activity of the NE trending faults is different in different segments. The SW segment is a Quaternary fault, the middle segment is a Neogene fault, The NE is Paleogene. But the segment of the NW trending fault is not obvious. The average vertical displacement rate is about 0 015mm/a.

长江口海域新生代地层与断裂活动性初探

长江口海域通过浅层人工地震勘察查明 ,新生代地层可分为 5个地震层。分别为第四系、上新统、中新统上段、中新统下段及始新统。第三纪地层自东北向西南依次超覆、减薄尖灭 ,上部被第四纪地层不整合覆盖。沉积基底主要由晚侏罗世火山岩系及燕山晚期酸性小岩体构成 ,未发现早第三纪及晚白垩世断陷盆地。断裂构造很发育 ,按展布方向大体可归为北东、北西及近东西向 3组 ,皆为正断层。前两者数量多、延伸长、断距大 ,与同区的航磁异常构架吻合。北东向断裂分段明显 ,西南段为第四纪断裂 ,中段为晚第三纪断裂 ,东北段为早第三纪断裂 ;而北西向断裂分段不很清晰。两者的垂直位移速率平均在 0 0 1 5mm a。本文对该海域有关的几个地质问题进行了讨论。

长江口海域断裂第四纪活动性特征

通过浅层人工地震勘察获知 ,长江口海域断裂构造发育 ,以北东、北西向断裂为主 .断裂以上新世 -早更新世活动为主 ,最新活动可至中更新世 .断裂的最大断距一般为几十米 ,往上断距变小 ,中更新统底界的断距在 12～ 13m .断裂平均垂直位移速率为 10 - 3mm/a量级 .

长江口海域地质灾害研究

根据地矿部上海海洋地质调查局1973年以来,在东海及长江口海域进行的大量地球物理调查、海洋地质及石油地质调查的基础上,收集了解其他单位所做成果,对长江口海域的地质灾害开展专项研究,结合海域环境地质、工程地质条件,进行综合分析,以了解和查明海域存在的地质灾害类型、规模、分布、特征等,为海域地质灾害的防御和减灾提出对策,为长江口海域、上海浦东及东海油气田的开发建设提供决策依据。