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Frequency and initiation mechanisms of submarine slides on the Fraser Delta front.

机译：弗雷泽三角洲前缘海底滑坡的频率和起爆机制。

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摘要

The Fraser delta hosts a population of over 500,000 including the municipalities of Richmond and Delta and the Vancouver International Airport. The main arm of the Fraser River has been fixed in place by construction of a jetty focusing sediment deposition on the Sand Heads area. There is a history of submarine slide events at the delta crest which pose substantial risk to coastal infrastructure near the delta front. A submarine channel, characterized by prominent levee deposits, extends seaward from the Sand Heads area.;In this study, sand beds in cores from levee overspill deposits are dated using excess 210Pb activity. They are interpreted as the downstream deposits of channelized turbidity currents generated by liquefied slide material. Sedimentation is characterized by sandy mud, interpreted to be deposited continuously by river plume suspension fall-out, and two distinct kinds of sand beds which represent two genetically different processes. The first type of sand bed (Facies 6) is thick, sharp based and clean, often showing classic Bouma turbidite elements including a massive sand base with laminated sands fining up to a mud top and is interpreted as the deposit from slides involving large volumes of material at the upper reaches of the tributary channels. The second type of sand bed (Facies 5) is characterized by muddy sand, has gradational contacts, and is interpreted as a low density deposit from either river generated turbidity currents or distal turbidites from smaller slide events. Facies 6 sand beds often occur as sets of 2 to 4 beds and individual bed sets have been dated to approximately the same ages of known large-scale slide events. Facies 5 sand beds occur more frequently and generally occur after periods with high flow.;Sediment cores show three distinct phases of levee growth within the past 100 years approximately. A basal phase consists of very thick beds of medium sand that are interpreted to represent the early stage of channel-levee evolution when continuous overspill occurs during turbidity current events. The second stage is characterized by thick sets of frequent Facies 6 fine grained sand beds separated by less than one year of mud deposition. These sand beds are interpreted as representing a period of levee growth where channel relief is low and overspill events occur often. The third phase is characterized by thick mud intervals with less frequent fine sand beds. Phase 3 is interpreted to reflect a state when levee growth has increased channel relief to a height greater than that of the typical channelized turbidity current. In the third phase, sediment bypass is common and only larger density flows are capable of spilling onto the levees. Deposits interpreted to represent large slides have a return interval of 10 to 15 years during the past 40 years. Deposits of smaller events occur on average every four to five years. Event ages are compared to large spring floods from the Fraser River and seismic activity to determine any causal relationship. There is some relationship between ages of event beds and river flood years, but the largest sand beds do not correspond to unusually large flood years or seismic activity. It is concluded that there are likely a combination of factors which contribute to slope failure including over steepening and increased pore pressure.
机译：弗雷泽三角洲地区人口超过500,000，其中包括里士满和三角洲的直辖市以及温哥华国际机场。弗雷泽河（Fraser River）的主要支臂已经通过在泥沙头（Sand Heads）地区集中沉积物的码头建造而得以固定。三角洲海底有滑坡事件，对三角洲前缘附近的沿海基础设施构成重大风险。海底河道以突出的堤防沉积物为特征，从沙头角地区向海延伸。在这项研究中，堤防溢流沉积物岩心中的沙床利用过量的210Pb活度确定了日期。它们被解释为由液化滑动材料产生的通道化浊流的下游沉积物。沉积物的特征是沙质泥浆（被解释为由河羽悬浮物沉降物连续沉积）和两种不同的沙床，代表了两个遗传上不同的过程。第一种砂床（Facies 6）厚，锋利且清洁，通常显示出经典的Bouma浊质元素，包括巨大的砂底和夹层砂细化至泥顶，并被解释为涉及大量泥沙的滑坡中的沉积物。支流上游的物质。第二种类型的砂床（相5）的特征是泥泞，具有分级接触，并被解释为由河流产生的浊流或较小的滑动事件产生的远层浊石的低密度沉积物。通常有6个沙床，每组2至4个床，而单个床的年代大约与已知的大规模滑坡事件的年龄相同。相5沙床的发生频率较高，通常发生在高流量时期之后。沉积物芯在大约100年内显示出三个不同的堤防增长阶段。基础阶段由非常厚的中砂层组成，这些层被解释为代表在浑浊的当前事件中连续溢流发生时河道堤坝演变的早期阶段。第二阶段的特征是频繁相6细粒砂床的厚套，相隔不到一年的泥浆沉积。这些沙床被解释为代表了堤防增长的一段时期，在此期间，河道起伏很低，并且经常发生溢油事故。第三阶段的特征是泥浆间隔较厚，细砂床的频率较低。第3阶段被解释为反映堤坝的增长使河道起伏增加到比典型的河道浊流高的高度的状态。在第三阶段，沉积物绕行很常见，只有较大的密度流才能够溢出到堤坝上。在过去40年中，被解释为代表大型滑坡的沉积物的回报间隔为10到15年。较小事件的存款平均每四到五年发生一次。将事件年龄与来自弗雷泽河（Fraser River）的春季大洪水和地震活动进行比较，以确定任何因果关系。事件床的年龄与河流洪水的年限之间存在一定的关系，但最大的沙床并不对应于异常大的洪水年或地震活动。结论是，可能有多种因素导致斜坡破坏，包括过度陡峭和孔隙压力增加。

著录项

  • 作者

    Stacey, Cooper D.;

  • 作者单位

    University of Victoria (Canada).;

  • 授予单位 University of Victoria (Canada).;
  • 学科 Sedimentary Geology.;Hydrology.
  • 学位 M.Sc.
  • 年度 2014
  • 页码 150 p.
  • 总页数 150
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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