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Rafael C. Carvalho David M. Kennedy Yakufu Niyazi Chloe Leach Teresa M. Konlechner Daniel Ierodiaconou 《地球表面变化过程与地形》2020,45(11):2540-2555
Historical aerial photographs are an invaluable tool in shoreline mapping and change detection in coastal landscapes. We evaluate the extent to which structure-from-motion (SfM) photogrammetric methods can be applied to quantify volumetric changes along sandy beaches, using archival imagery. We demonstrate the application of SfM-derived digital surface models (DSMs) at East Beach and Lady Bay in southwest Victoria, Australia, using photographic datasets taken in 1969, 1977 and 1986, and compare them to LiDAR-derived DSMs acquired at both sites in 2007. The SfM approaches resulted in two entire and two partial suitable DSMs out of six datasets. Good-quality DSMs were spatially continuous with a good spread of ground control points (GCPs) near the beach at Lady Bay, whereas unsuitable DSMs were mostly restricted by poor distribution and number of GCPs in spatially segmented areas of East Beach, due to limited overlapping of images, possible poor quality of GCPs and also the propagation of errors in the derived point clouds. A volume of approximately 223 000 ± 72 000 m3 was deposited at Lady Bay between 1969 and 2007, despite minimal erosion observed near the breakwater. The partially suitable dataset of East Beach indicated that beach erosion of at least 39 m3 m−1 occurred immediately to the east of the seawall after 1977. We also discuss the drawbacks and strengths of SfM approaches as a benchmark of historical erosion assessments along sandy beaches. © 2020 John Wiley & Sons, Ltd. 相似文献
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A method is presented to quantify the inelastic seismic resistance of reinforced concrete stack-like structures by non-linear earthquake analysis. The deformed configuration of stack is idealized as an assemblage of beam elements and actual stress–strain relationships of concrete and reinforcing steel are used to evaluate element matrices. Repeated non-linear analyses are performed by gradually increasing the intensity of acceleration time histories to a level where collapse of the stack is observed in primary stresses. The set of time histories thus obtained are then used to define the ultimate intensity of ground motion that the stack can sustain if inelastic deformations are permitted. A procedure is presented to quantify the difference between inelastic seismic resistance and elastic seismic resistance in terms of displacement ductility capacity factors. For seismic design using available inelastic resistance, values of curvature ductility factor demand for the cross-sections of stacks are also presented. © 1997 by John Wiley & Sons, Ltd. 相似文献
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Analyses of deterioration of the Cappadocian tuff, Turkey 总被引：8，自引：3，他引：5
The Cappadocian tuff contains unique erosional features, the so-called fairy chimneys, some of which in the past were dwelled
in and contain valuable wall paintings. These historical heritages, however, are undergoing chemical and physical deterioration
due to atmospheric effects. For the conservation studies, understanding of the deterioration phenomenon of the tuff is essential.
In this study, engineering geological and physicochemical characteristics of the tuff were determined. The durability of the
tuff was assessed through wetting-drying, freezing-thawing, and salt crystallization. The test results suggest that chemical
weathering may be traced to a depth of 2 cm below lichen-covered surfaces and 20 cm adjacent to discolored joint walls. Based
on durability assessment methods, the tuff may be classified as having poor to very poor durability.
Received: 16 December 1996 · Accepted: 3 April 1997 相似文献
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The origin of the so-called “fairy circles” has not yet been established. Carbon monoxide (as an indicator of a natural gas microseep) was monitored inside and outside of the selected fairy circles in the Namib, Namibia, Southern Africa. Hydrocarbons were extracted from the soil by a novel method for trapping analytes onto silicone rubber designed for thermal desorption into a gas chromatograph-mass spectrometer (GC-MS). Unresolved complex mixtures with resolvable alkanes were detected in soil collected from two newly formed circles. Alkenes, the microbial degradation product of alkanes (microbial food source), were more abundant in the circles compared to the levels of alkenes detected in the matrix between circles. Results show a microseepage of gases and hydrocarbons which is expressed at the surface as a geobotanical anomaly of barren circles and circles of altered vegetation. In addition, this finding may suggest a new approach to the origin of the mima mounds (heuweltjies) of the Western Cape in South Africa. 相似文献
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Derman Dondurur Günay ÇifçiMahmut Göktu? Drahor Süleyman Co?kun 《Marine and Petroleum Geology》2011,28(8):1505-1516
Based on high-resolution Chirp seismic, multibeam bathymetry and side scan sonar data collected in the ?zmir Gulf, Aegean Sea in 2008 and 2010, gas-related structures have been identified, which can be classified into three categories: (1) shallow gas accumulations and gas chimneys, (2) mud diapirs, and (3) active and inactive pockmarks. On the Chirp profiles, shallow gas accumulations were observed along the northern coastline of the outer ?zmir Gulf at 3-20 m below the seabed. They appear as acoustic turbidity zones and are interpreted as biogenic gas accumulations produced in organic-rich highstand fan sediments from the Gediz River. The diapiric structures are interpreted as shale or mud diapirs formed under lateral compression due to regional counter-clockwise rotation of Anatolian microplate. Furthermore, the sedimentary structure at the flanks suggests a continuous upward movement of the diapirs. Several pockmarks exist close to fault traces to the east of Hekim Island; most of them were associated with acoustic plumes indicating active degassing during the survey period in 2008. Another Chirp survey was carried out just over these plumes in 2010 to demonstrate if the gas seeps were still active. The surveys indicate that the gas seep is an ongoing process in the gulf. Based on the Chirp data, we proposed that the pockmark formation in the area can be explained by protracted seep model, whereby sediment erosion and re-distribution along pockmark walls result from ongoing (or long lasting) seepage of fluids over long periods of time. The existence of inactive pockmarks in the vicinity, however, implies that gas seepage may eventually cease or that it is periodic. Most of the active pockmarks are located over the fault planes, likely indicating that the gas seepage is controlled by active faulting. 相似文献
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南海北部烟囱状冷泉碳酸盐岩的沉积环境分析 总被引：2，自引：2，他引：0
对南海北部陆坡具有圈层结构的烟囱状冷泉碳酸盐岩的岩石学、矿物学和地球化学特征进行了研究,结果表明:烟囱内外层具有明显不同的特征,内层碳酸盐含量比外层高,内层的碳酸盐矿物也更富含MgCO3,并且矿物颗粒较大,结晶程度较高;外层的铝、硅等陆源碎屑元素比内层含量高。内外层的碳、氧同位素也具有明显差别。对于研究的两个样品,内层的δ13 C分别为-40.80×10-3和-31.27×10-3,δ18 O分别为2.67×10-3和2.00×10-3,而外层的δ13 C分别为-31.26×10-3和-30.99×10-3,δ18 O分别为0.48×10-3和1.85×10-3。结合前人在该区域附近的研究结果认为,烟囱状碳酸盐岩具有内层比外层相对较负δ13C和较为富集δ18 O的特征。1mm间隔取样的δ13C和δ18 O剖面变化与烟囱状碳酸盐岩的圈层结构吻合较好,由外层至内层δ13C的变化范围为-27.50×10-3～-32.05×10-3,δ18 O的变化范围为0.78×10-3～2.34×10-3。外层6mm的δ13 C和δ18 O具有明显的负线性相关,相关系数r2为0.996 7。根据上述特征,讨论了渗漏甲烷流体的性质、扩散机制及对沉积环境的影响,推测具有圈层结构的烟囱状碳酸盐岩是由单一渗漏通道形成的,生长顺序有待进一步定年证实。烟囱外部6mm受海水影响较大。研究结果对于恢复南海北部陆坡甲烷渗漏系统、建立冷泉和热泉之间的联系具有一定意义。 相似文献
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现代海底热液成矿作用研究现状及发展方向 总被引：15，自引：0，他引：15
现代海底热水成矿作用研究的重大进展表现在两个方面：（１）大批活动的和窒息的热液活动区和硫化物矿床在洋脊、岛弧、弧后盆地及板内火山活动中心等海底环境相继发现。在沉积物饥饿洋脊，矿床规模较小，Ｃｕ－Ｚｎ为主，沉积物覆盖洋脊，矿床规模巨大，Ｐｂ－Ｚｎ为主。弧后扩张或弧间裂陷盆地，形成Ｐｂ－Ｚｎ→Ｚｎ－Ｐｂ－Ｃｕ→Ｃｕ－Ｚｎ矿床谱系。岛弧环境硫化物矿床不具规模，板内火山活动中心以氧化物－硫化物矿化为特色。（２）现代海底热水成矿作用观察和研究为古代ＶＭＳ矿床成因研究提供了重要信息，对现有成矿理论产生重要影响。现代成矿观念强调：①海底成矿作用虽可产生于不同环境，但均与张裂断陷事件密切相关。矿床规模和分布特点受张裂速率制约；②成矿物质主体来源于热水循环的火山－沉积岩和下伏基底物质；③硫化物堆积发生于丘堤－烟囱联合构成的机构和结壳下部，通过开放空间的硫化物充填和先成矿石淋滤迁移来实现。④热液流体呈双扩散对流循环。现代海底热水成矿作用的未来研究方向可概括为强度方向和广度方向。广度研究将加大力度去发现新的矿床，强度研究将采用地球物理方法并配以必要的钻探，深入揭示矿床的三维结构和热液体系及成矿机制。 相似文献
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南海北部活动构造及其对天然气水合物的影响 总被引：1，自引：0，他引：1
海底天然气水合物与活动构造关系极为密切,随着近十几年来海底天然气水合物勘探与研究取得的重要进展,相关活动构造也正在逐渐受到关注。通过对断裂、地震、气底辟以及海底火山活动等构造活动的多种表现形式的研究,分析了南海北部活动构造的特征。在南海北部,存在北东向、北东东-东西向、北西向3组活动断裂,其中北西向断裂切割其他两组,形成最晚。这些活动断裂以继承性为主,北东向和北东东向断裂均为切割地壳或岩石圈的大断裂。南海北部的震中呈带状分布,在东部呈北东走向,而西部受红河走滑断裂的影响,震中整体为北西走向分布。气底辟是对天然气水合物形成有重要指示意义的构造,同断裂一样,气底辟为气源垂直向上移动至形成水合物的温压带提供了良好的通道。南海北部分布的火山岩由东到西顺时针旋转。从地震剖面可以看出,岩体明显受张性断裂控制。东部天然气水合物的分布受北西向活动断层的影响较大,而西部则与海底滑坡密不可分。 相似文献