Sedimentary Deposits from the 17 July 2006 Western Java Tsunami, Indonesia: Use of Grain Size Analyses to Assess Tsunami Flow Depth, Speed, and Traction Carpet Characteristics
Sedimentary Deposits from the 17 July 2006 Western Java Tsunami, Indonesia: Use of Grain Size Analyses to Assess Tsunami Flow Depth, Speed, and Traction Carpet Characteristics
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2006 年 7 月 17 日印度尼西亚西爪哇海啸的沉积物：利用粒度分析评估海啸流深度、速度和牵引毯特征
DOI：
10.1007/s00024-011-0280-8
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发表时间：
2011
影响因子：
2
通讯作者：
C. Synolakis
中科院分区：
文献类型：
--
作者：
A. Moore;James R. Goff;B. McAdoo;H. Fritz;A. Gusman;N. Kalligeris;Kenia Kalsum;Arif Susanto;Debora Suteja;C. Synolakis
2006年的西爪哇海啸沉积了一层厚达20厘米的不连续的沙层，淹没了爪哇南部沿海至少8米深，并淹没了内陆1公里。在大多数地方，主要是重矿物砂席通常是分级的，在一些地方，它包含复杂的内部地层。沙层内的结构可能记录了多达两个单独的波浪的通过，这一点在目击者的描述中得到了注意。我们详细研究了2006年海啸沉积物沿着一个流动平行样带约750米长，15公里的Cilacap。海啸存款首先变得可辨从下面的沉积物70米的海岸线。从75至300米的内陆存款已奠定了稻田，并保持10-20厘米的厚度。向陆地300米处，存款急剧变薄，达到1毫米乘450米的内陆。从450 m到沉积物边缘（内陆约700 m），存款厚度仍小于1 mm。沉积通常伴随着洪水--沿着横断面，海啸将沙子沉积到洪水极限约40 m以内。存款较厚的部分主要含有沙子，与事件发生后3周在海滩上发现的沙子没有区别，但在大约450 m后（大致与厚度的减少一致），海啸沉积物转变为更像下面的水稻土，而不是海滩沙子。存款内的颗粒大小往往罚款向上和向陆地，虽然整体向上细化发生在两个离散的脉冲，与一个反级配的初始部分，然后是一个部分的正常级配。这两个相反梯度的部分也是密度梯度的，在底部有更密集的颗粒，在顶部有更少的密度颗粒。这两个正常级配的部分没有显示密度趋势。反梯度剖面显示，底部沉积物密度高，向上密度变小，代表海啸底部的牵引毯流。这些都表明在流动中的高剪切速率。由于牵引毯中的颗粒分选，通常在海啸沉积物中看到的向陆细化趋势被掩盖，尽管平均沉积物粒度沿着断面的横向变化确实显示出整体向陆细化，随着存款逐渐减少，变化更大。在更靠海的部分，存款也比没有牵引地毯的海啸产生的厚。
The 2006 western Java tsunami deposited a discontinuous sheet of sand up to 20 cm thick, flooded coastal southern Java to a depth of at least 8 m and inundated up to 1 km inland. In most places the primarily heavy mineral sand sheet is normally graded, and in some it contains complex internal stratigraphy. Structures within the sand sheet probably record the passage of up to two individual waves, a point noted in eyewitness accounts. We studied the 2006 tsunami deposits in detail along a flow parallel transect about 750 m long, 15 km east of Cilacap. The tsunami deposit first becomes discernable from the underlying sediment 70 m from the shoreline. From 75 to 300 m inland the deposit has been laid down in rice paddies, and maintains a thickness of 10–20 cm. Landward of 300 m the deposit thins dramatically, reaching 1 mm by 450 m inland. From 450 m to the edge of deposition (around 700 m inland) the deposit remains <1 mm thick. Deposition generally attended inundation—along the transect, the tsunami deposited sand to within about 40 m of the inundation limit. The thicker part of the deposit contains primarily sand indistinguishable from that found on the beach 3 weeks after the event, but after about 450 m (and roughly coinciding with the decrease in thickness) the tsunami sediment shifts to become more like the underlying paddy soil than the beach sand. Grain sizes within the deposit tend to fine upward and landward, although overall upward fining takes place in two discrete pulses, with an initial section of inverse grading followed by a section of normal grading. The two inversely graded sections are also density graded, with denser grains at the base, and less dense grains at the top. The two normally graded sections show no trends in density. The inversely graded sections show high density sediment to the base and become less dense upward and represents traction carpet flows at the base of the tsunami. These are suggestive of high shear rates in the flow. Because of the grain sorting in the traction carpet, the landward-fining trends usually seen in tsunami deposits are masked, although lateral changes of mean sediment grain size along the transect do show overall landward fining, with more variation as the deposit tapers off. The deposit is also thicker in the more seaward portions than would be produced by tsunamis lacking traction carpets.