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1.
Christopher F. Waythomas Philip Watts Fengyan Shi James T. Kirby 《Quaternary Science Reviews》2009,28(11-12):1006-1019
We analyze mass-flow tsunami generation for selected areas within the Aleutian arc of Alaska using results from numerical simulation of hypothetical but plausible mass-flow sources such as submarine landslides and volcanic debris avalanches. The Aleutian arc consists of a chain of volcanic mountains, volcanic islands, and submarine canyons, surrounded by a low-relief continental shelf above about 1000–2000 m water depth. Parts of the arc are fragmented into a series of fault-bounded blocks, tens to hundreds of kilometers in length, and separated from one another by distinctive fault-controlled canyons that are roughly normal to the arc axis. The canyons are natural regions for the accumulation and conveyance of sediment derived from glacial and volcanic processes. The volcanic islands in the region include a number of historically active volcanoes and some possess geological evidence for large-scale sector collapse into the sea. Large scale mass-flow deposits have not been mapped on the seafloor south of the Aleutian Islands, in part because most of the area has never been examined at the resolution required to identify such features, and in part because of the complex nature of erosional and depositional processes. Extensive submarine landslide deposits and debris flows are known on the north side of the arc and are common in similar settings elsewhere and thus they likely exist on the trench slope south of the Aleutian Islands. Because the Aleutian arc is surrounded by deep, open ocean, mass flows of unconsolidated debris that originate either as submarine landslides or as volcanic debris avalanches entering the sea may be potential tsunami sources.To test this hypothesis we present a series of numerical simulations of submarine mass-flow initiated tsunamis from eight different source areas. We consider four submarine mass flows originating in submarine canyons and four flows that evolve from submarine landslides on the trench slope. The flows have lengths that range from 40 to 80 km, maximum thicknesses of 400–800 m, and maximum widths of 10–40 km. We also evaluate tsunami generation by volcanic debris avalanches associated with flank collapse, at four locations (Makushin, Cleveland, Seguam and Yunaska SW volcanoes), which represent large to moderate sized events in this region. We calculate tsunami sources using the numerical model TOPICS and simulate wave propagation across the Pacific using a spherical Boussinesq model, which is a modified version of the public domain code FUNWAVE. Our numerical simulations indicate that geologically plausible mass flows originating in the North Pacific near the Aleutian Islands can indeed generate large local tsunamis as well as large transoceanic tsunamis. These waves may be several meters in elevation at distal locations, such as Japan, Hawaii, and along the North and South American coastlines where they would constitute significant hazards. 相似文献
2.
公路弃渣泥石流物源集中,弃渣类型是泥石流成灾机制的重要影响因素。砂岩类弃渣中粘粒含量小,膨胀性较弱,弃渣体内水体排泄通畅,不利于孔隙水压的保持,相比灰岩类弃渣自身稳定性高;但在暴雨作用下,弃渣体内水分增加大于排泄,易造成弃渣体的崩滑起动,形成小型的泥石流,多形成稀性泥石流;灰岩类弃渣中粘粒的膨胀性较高,弃渣体孔隙水压易增大,渣土体的稳定性差,在暴雨作用下,弃渣中的土体易膨胀液化、滑移起动,多形成粘性泥石流;灰岩类弃渣泥石流规模大于砂岩类弃土。本文从弃渣物理性质指标、力学特征等研究泥石流成灾机制,并致力于将成果应用到公路弃土场设计和防灾减灾领域。 相似文献
3.
Anne Le Friant Georges Boudon Jean-Christophe Komorowski Christine Deplus 《Comptes Rendus Geoscience》2002,334(4):235-243
Results from recent fieldwork and the Aguadomar marine survey in the Lesser Antilles clearly indicate that the volcanic field of southern Dominica has experienced three major edifice collapse events. This led to formation of the most voluminous debris avalanches known in the Caribbean Arc. Submarine hummocky morphology with plurikilometric megablocks is characteristic of debris avalanche deposits. We propose that steep slopes on the western Caribbean side of the island and intense hydrothermal alteration lead to recurrent large-scale edifice collapses. Therefore islands in the Lesser Antilles face a non-negligible risk from generation of tsunamis associated with potential future edifice collapse. To cite this article: A. Le Friant et al., C. R. Geoscience 334 (2002) 235–243. 相似文献
4.
Amr Z. Hamouda 《Environmental Earth Sciences》2014,71(12):5045-5058
The study area lies between 31.32°N, 31.70°E and 31.41°N, 31.78°E along Damietta branch, Nile River. It is about 24-km long. Acoustic classification (Quester Tangent Corporation—QTC) is used as a powerful tool to study seabed characteristics which is confirmed by the sediment analyses. Sediment characteristics of the study are presented by three acoustic classes: sand, mud and organic matter intercalated by clay. The depth varies from about ?12 m at Faraskour Bridge (southern part of the study area) to about ?2.5 m at Faraskour Dam (northern part of the study area). The average current velocity is detected as 4 cm/s and it has a very low effect on the transport of both sediment and waste debris. The sediment in the northern part characterized by organic matter reaches about 70 cm thickness under and around fish cages. This huge amount of organic matter deposit leads to the reduction of the dissolved oxygen and increase pH values. This study shows that the water quality in the northern part of the study area is at risk (drinking water for Damietta city) due to the presence of the huge amount of waste debris intercalated by organic matter. The rises of temperature in summer enhance oxygen consumption and the decomposition of the organic matter. This is rapidly increasing the growth of bacteria and phytoplankton, causing turbidity and algal blooms. Those affect the water quality and raise the water toxicity (drinking water). 相似文献
5.
Tsunami deposits in the geological record 总被引：2，自引：0，他引：2
A review is presented here of tsunami deposits in the geological record. It begins with a discussion of the relationships between the processes of tsunami generation and propagation and the sedimentary responses. This is followed by a consideration of the sedimentary processes associated with the passage of tsunami waves across coastlines. Attention is also given to the sedimentary processes associated with tsunami-triggered gravity backwash flows and comparisons are made with turbidity current action. We observe that despite sedimentary evidence for recent tsunamiites, geological research on ancient tsunamis has not identified stratigraphic units associated with onshore tsunami sedimentation. Equally, it is noted that nearly all published studies of sedimentary processes associated with modern tsunamis have not considered patterns of sediment transport and deposition in the offshore zone. 相似文献
6.
A number of examples are presented to substantiate that submarine landslides have occurred along most continental margins and along several volcano flanks. Their properties of importance for tsunami generation (i.e. physical dimensions, acceleration, maximum velocity, mass discharge, and travel distance) can all gain extreme values compared to their subaerial counterparts. Hence, landslide tsunamis may also be extreme and have regional impact. Landslide tsunami characteristics are discussed explaining how they may exceed tsunamis induced by megathrust earthquakes, hence representing a significant risk even though they occur more infrequently. In fact, submarine landslides may cause potentially extreme tsunami run-up heights, which may have consequences for the design of critical infrastructure often based on unjustifiably long return periods. Giant submarine landslides are rare and related to climate changes or glacial cycles, indicating that giant submarine landslide tsunami hazard is in most regions negligible compared to earthquake tsunami hazard. Large-scale debris flows surrounding active volcanoes or submarine landslides in river deltas may be more frequent. Giant volcano flank collapses at the Canary and Hawaii Islands developed in the early stages of the history of the volcanoes, and the tsunamigenic potential of these collapses is disputed. Estimations of recurrence intervals, hazard, and uncertainties with today’s methods are discussed. It is concluded that insufficient sampling and changing conditions for landslide release are major obstacles in transporting a Probabilistic Tsunami Hazard Assessment (PTHA) approach from earthquake to landslide tsunamis and that the more robust Scenario-Based Tsunami Hazard Assessment (SBTHA) approach will still be most efficient to use. Finally, the needs for data acquisition and analyses, laboratory experiments, and more sophisticated numerical modelling for improved understanding and hazard assessment of landslide tsunamis are elaborated. 相似文献
7.
In the seventeenth century, two tsunamis that were generated by earthquakes on the Kuril–Kamchatka subduction zone inundated the eastern coast of Hokkaido, northern Japan. Stratigraphic evidence for these two tsunamis and related land-level change in coastal Hokkaido consists of two landward-thinning sand layers in the sediments of Lake Tokotan, a coastal lagoon on the Hokkaido coast. The marine origin of these sand layers is indicated by the presence of brackish–marine diatoms. The rarity and high degree of fragmentation of diatom valves suggests that the sands were transported in a short time over a considerable distance. Tsunamis at this site were probably generated by great earthquakes along the Kuril–Kamchatka Trench. Volcanic ash deposits lying just above the sands suggest that tsunamis occurred in the late 17th century. Tsunamis during the historic period are not recorded in Lake Tokotan, which suggests that the sand layers were deposited by tsunamis substantially larger than historic tsunamis. 相似文献
8.
The major earthquake-induced tsunamis reliable known to have occurred in and near Greece since antiquity are considered in the light of the recently obtained reliable data on the mechanisms and focal depths of the earthquakes occurring here. (The earthquake data concern the major shocks of the period 1962–1986.) First, concise information is given on the most devastating tsunamis. Then the relation between the (estimated) maximum tsunami intensity and the earthquake parameters (mechanism and focal depth) is examined. It is revealed that the most devastating tsunamis took place in areas (such as the western part of the Corinthiakos Gulf, the Maliakos Gulf, and the southern Aegean Sea) where earthquakes are due to shallow normal faulting. Other major tsunamis were nucleated along the convex side of the Hellenic arc, characterized by shallow thrust earthquakes. It is probably somewhere there (most likely south of Crete) that the region's largest known tsunami occurred in AD 365, claiming many lives and causing extensive devastation in the entire eastern Mediterranean. Such big tsunamis seem to have a return period of well over 1000 years and can be generated by large shallow earthquakes associated with thrust faulting beneath the Hellenic trench, where the African plate subduces under the Euroasian plate. Lesser tsunamis are known in the northernmost part of the Aegean Sea and in the Sea of Marmara, where strike-slip faulting is observed. Finally, an attempt is made to combine the tsunami and earthquake data into a map of the region's main tsunamigenic zones (areas of the sea bed believed responsible for past tsunamis and expected to nucleate tsunamis in the future). 相似文献
9.
Destructive tsunamis are infrequent comparedwith other natural disasters, andtheir evidences tend to disappear quickly.Conventional data acquisition havebeen limited in coverage and tend to beunreliable. Readily available andtransient data should be collectedby field survey teams as soon as possible.Since tsunamis are always triggered by the simultaneous or in-advanceoccurrence of another phenomena, they can be considered close to thesource as a syndrome, leaving a variety of almost simultaneous effectsat the nearby coasts. By observating the evidence left bythese local interaction effects, the surveyors should be able to identifyand evaluate at least the maximum horizontal extension and the verticalreach of the inundation. High water marks and lines of landward limitof sea grass, debris or sediment deposited, may help in this identification and measurement process.Guidelines to conduct post-tsunami field surveys and standards for theobservations have been established by the International Coordination Groupfor the Tsunami Warning System in the Pacific (ICG/ITSU) upon agreement with the scientific community. A Post-Tsunami Survey Field Guide was published by the Intergovernmental Oceanographic Commission (IOC) of UNESCO. 相似文献
10.
海啸作为五大海洋自然灾害之一,严重威胁着人类生命财产安全。近些年来,国内外学者对地震海啸进行了大量研究,主要针对海啸的生成、传播、爬高和淹没的数值模拟,以及古海啸沉积物进行研究,但是对于海啸地震震源机制的研究还比较欠缺,尤其是缺乏对震级小于6.5的海啸地震的研究。针对我国的地震海啸研究现状,强调震级小于6.5地震引发海啸的问题不容忽视。本文归纳整理了全球766次地震海啸,利用三角图分类基本法则对海啸地震震源机制解进行分类,并对其中341个发生在1976年后的海啸地震进行震源机制解分析,对其中633次海啸浪高进行统计学方法分析研究。本文认为逆冲型、正断型、走滑型和奇异型机制地震均能引发海啸,逆冲型地震引发的海啸占比最大,震级小于6.5级地震引发的海啸的浪高也有高达10 m的情况,也能产生巨大破坏性。逆冲型、正断型、奇异型地震可直接引起海底地形垂向变化,进而引发海啸,而走滑型地震引发海啸则可能有两种原因,一种是走滑型地震并非纯走滑型而是带有正断或逆冲分量从而引发海啸,另外一种是走滑型地震引发海底滑坡导致海底地形变化进而产生海啸。从海啸地震震源深度分析,能产生海啸的地震震源深度97%以上都是浅源地震,主要集中在30 km深度以内,但是也有中深源地震海啸。本文综合海啸地震的震源特点、我国地理位置以及以往海啸发生的情况,认为未来我国沿海地区威胁性的地震海啸主要集中在马尼拉海沟和台湾海峡区域,在今后海啸预警方面需要格外重视这些区域,通过建立完善海啸预警系统来减少损失。 相似文献
11.
Dislocated boulders are one sign of high-energy wave impacts on coasts. These high-energy impacts, caused by severe storms or tsunamis, can trigger initial cracking and transport of boulders. Monitoring of these boulders, as well as the associated coastal sites is important in distinguishing between gradual coastal processes and high-energy events. Western Greece is a seismically active area, where tsunamis and high-energetic storms might occur and such past events are documented by historic and geoscientific research, making it an ideal location for monitoring dislocated boulders. Since 2008, monitoring of eight different coastal sites in this region was conducted by terrestrial laser scanning and photogrammetric approaches, with low-cost unmanned aerial vehicles. The re-use of similar surveying points in following years, allowed highly accurate monitoring. Point clouds derived from these methods were evaluated for change detection by point cloud comparisons. The data were also used to establish accurate three-dimensional models of dislocated boulders (n = 70). The determined boulder volumes of these accurate three-dimensional models were incorporated in wave transport equations and wave decay curves, and compared with monitoring results. A comprehensive overview of dislocated boulders in western Greece is presented. Three-dimensional boulder reconstruction is compared to an approach which uses a tape-based measuring of boulder axes, with the tape-based measurement showing a mean overestimation of mass by 32%. Accurate monitoring over time by both methods, is achieved by using fixed networks of reference points. Changes for each site over time, detected by direct point cloud comparisons, are fit to the possible inundation calculated by wave decay curves based on computed minimum wave heights for boulder transport. Both storm and tsunami waves may have initiated movement from the cliff edge and further transport is also possible. However, boulders showed no further movement from their current position in the area for the time period of this study. 相似文献
12.
A tsunami catalogue for Central America is compiledcontaining 49 tsunamis for the period 1539–1996,thirty seven of them are in the Pacific and twelve inthe Caribbean. The number of known tsunamis increaseddramatically after the middle of the nineteenth century,since 43 events occurred between 1850 and 1996. This isprobably a consequence of the lack of populationliving near the coast in earlier times.The preliminary regionalization of the earthquakessources related to reported tsunamis shows that, inthe Pacific, most events were generated by theCocos-Caribbean Subduction Zone (CO-CA). At theCaribbean side, 5 events are related with the NorthAmerican-Caribbean Plate Boundary (NA-CA) and 7 withthe North Panama Deformed Belt (NPDB).There are ten local tsunamis with a specific damagereport, seven in the Pacific and the rest in theCaribbean. The total number of casualties due to localtsunamis is less than 455 but this number could behigher. The damages reported range from coastal andship damage to destruction of small towns, and theredoes not exist a quantification of them.A preliminary empirical estimation of tsunami hazardindicates that 43% of the large earthquakes (Ms 7.0) along the Pacific Coast of Central America and100% along the Caribbean, generate tsunamis. On thePacific, the Guatemala–Nicaragua coastal segment hasa 32% probability of generating tsunamis after largeearthquakes while the probability is 67% for theCosta Rica–Panama segment. Sixty population centers onthe Pacific Coast and 44 on the Caribbean are exposedto the impact of tsunamis. This estimation alsosuggests that areas with higher tsunami potential inthe Pacific are the coasts from Nicaragua to Guatemalaand Central Costa Rica; on the Caribbean side, Golfode Honduras Zone and the coasts of Panama and CostaRica have major hazard. Earthquakes of magnitudelarger than 7 with epicenters offshore or onshore(close to the coastline) could trigger tsunamis thatwould impact those zones. 相似文献
13.
Tsunamis have occurred in Canada due to earthquakes, landslides, and a large chemical explosion. The Pacific coast is at greatest risk from tsunamis because of the high incidence of earthquakes and landslides in that region. The most destructive historical tsunamis, however, have been in Atlantic Canada – one in 1917 in Halifax Harbour, which was triggered by a catastrophic explosion on a munitions ship, and another in 1929 in Newfoundland, caused by an earthquake-triggered landslide at the edge of the Grand Banks. The tsunami risk along Canada's Arctic coast and along the shores of the Great Lakes is low in comparison to that of the Pacific and Atlantic coasts. Public awareness of tsunami hazard and risk in Canada is low because destructive tsunamis are rare events. 相似文献
14.
S. L. Soloviev 《Natural Hazards》1990,3(2):183-202
A list of 300 tsunamis and similar phenomena known in the Mediterranean is given. Data reliability and wave intensity are estimated; mechanisms of tsunami generation are indicated and data from literature sources on the coordinates and magnitudes of tsunamigenic earthquakes are cited. Eighteen zones of excitation and manifestation of tsunamis are identified which can be integrated into four groups with respect to the recurrence period and maximum intensity of the tsunamis. The strongest tsunamis are excited in the Aegean Sea, and the Hellenic and Calabrian island arcs. The focal depth of the earthquake-generating tsunamis in the Mediterranean is, on average, less than that in the Pacific. Correspondingly, the magnitude of tsunamigenic earthquakes is lower. According to preliminary estimates, the Mediterranean tsunamis attenuate with distance more rapidly than do those in the Pacific Ocean. 相似文献
15.
【研究目的】碎屑流是深水环境沉积物搬运和分散的重要机制,其相关的砂岩储层是含油气盆地重要的勘探目标,然而,与经典浊流及浊积系统相比,对碎屑流主控型深水体系的发育规律目前仍知之甚少。【研究方法】本文基于岩心、测井及全三维地震资料,通过系统的岩心观察描述、测井及地震资料解释,对渤海湾盆地东营凹陷始新统沙三中亚段深水体系沉积过程及模式开展研究。【研究结果】结果表明,沙三中深水体系发育九种异地搬运岩相,可概括为四大成因类型,反映了块体及流体两种搬运过程。岩相定量统计表明,该深水体系主要由碎屑流沉积构成,浊流沉积很少,碎屑流中又以砂质碎屑流为主。重力流在搬运过程中经历了滑动、滑塌、砂质碎屑流、泥质碎屑流及浊流等5个阶段演变,发育5类主要的深水沉积单元,包括滑动体、滑塌体、碎屑流水道、碎屑流朵体及浊积薄层砂。从发育规模及储层物性上,砂质碎屑流水道、朵体及砂质滑动体构成了本区最重要的深水储层类型。【结论】认为沙三中时期充足的物源供给、三角洲前缘高沉积速率、断陷期频繁的断层活动以及较短的搬运距离是碎屑流主控型深水体系形成及演化的主控因素,最终基于沉积过程、沉积样式及盆地地貌特征综合建立了碎屑流主控型深水体系沉积模式。本研究将进一步丰富深水沉积理论,为陆相深水储层预测提供借鉴。 相似文献
16.
水下碎屑流沉积是近年来在深水环境（深海或深湖）中日益受到重视的一种沉积类型,然而目前还没有一个确定水下沉积物的块体搬运过程的公认鉴别标志。通过对鄂尔多斯盆地湖盆中央地区几个露头剖面的地质调查,首次在延长组深水厚层块状砂岩中发现了一种“泥包砾”结构,并分析了其形成与演变过程。研究认为这种“泥包砾”结构主要与三角洲前缘特殊的“碎屑流”成因机理与发育过程有关,其形成过程自始自终表现出含有它的沉积物是作为块体状态（宾汉塑性体）被搬运的,自始自终表现出其在搬运过程中是被介质的强度所支撑的,据此认为“泥包砾”结构是确定延长组深水厚层块状砂岩为碎屑流成因的最有意义的标志性证据,并由此建立了延长组深水砂岩从开始启动到搬运、再到沉积的过程与模式。同时,本文认为“泥包砾”也为深海沉积中块体搬运作用与搬运过程的研究提供了一种可借鉴的关键性判识标志,对于当前全球深水（包括深海与深湖）油气勘探以及目前国际地学界广泛开展的大陆边缘沉积物“从源到汇”过程的研究都有积极意义。 相似文献
17.
A combination of numeric hydrodynamic models, a large-clast inverse sediment-transport model, and extensive field measurements were used to discriminate between a tsunami and a storm striking Anegada, BVI a few centuries ago. In total, 161 cobbles and boulders were measured ranging from 1.5 to 830?kg at distances of up to 1?km from the shoreline and 2?km from the crest of a fringing coral reef. Transported clasts are composed of low porosity limestone and were derived from outcrops in the low lying interior of Anegada. Estimates of the near-bed flow velocities required to transport the observed boulders were calculated using a simple sediment-transport model, which accounts for fluid drag, inertia, buoyancy, and lift forces on boulders and includes both sliding and overturning transport mechanisms. Estimated near-bed flow velocities are converted to depth-averaged velocities using a linear eddy viscosity model and compared with water level and depth-averaged velocity time series from high-resolution coastal inundation models. Coastal inundation models simulate overwash by the storm surge and waves of a category 5 hurricane and tsunamis from a Lisbon earthquake of M 9.0 and two hypothetical earthquakes along the North America Caribbean Plate boundary. A modeled category 5 hurricane and three simulated tsunamis were all capable of inundating the boulder fields and transporting a portion of the observed clasts, but only an earthquake of M 8.0 on a normal fault of the outer rise along the Puerto Rico Trench was found to be capable of transporting the largest clasts at their current locations. Model results show that while both storm waves and tsunamis are capable of generating velocities and temporal acceleration necessary to transport large boulders near the reef crest, attenuation of wave energy due to wave breaking and bottom friction limits the capacity of storm waves to transport large clast at great inland distances. Through sensitivity analysis, we show that even when using coefficients in the sediment-transport model which yield the lowest estimated minimum velocities for boulder transport, storm waves from a category 5 hurricane are not capable of transporting the largest boulders in the interior of Anegada. Because of the uncertainties in the modeling approach, extensive sensitivity analyses are included and limitations are discussed. 相似文献
18.
19.
凌云 《地质灾害与环境保护》2009,20(3):13-17
华安洋竹径502矿区地质灾害隐患为潜在矿渣泥石流,堆积坡面弃渣及尾矿库内矿渣是泥石流的物质来源,是该地质灾害隐患的主要治理对象。通过对不同治理方案的分析研究,认为工程治理投入资金较大,且仅能治标,不能完全排除泥石流隐患。通过对尾矿弃渣二次选矿,回收有价值的钨矿,废渣外运作为建材,最终恢复原始地貌。投资风险小,并可取得良好的社会效益和经济效益;在资源日益紧缺的时代,对处理类似地质灾害隐患提供一种有效途径。 相似文献
20.
Tsunami-induced scour at coastal roadways: a laboratory study 总被引：1，自引：1，他引：0
Coastal roads are lifelines for bringing emergency personnel and equipment into affected areas after tsunamis, thus careful thought should be given to how to make roadways safer from tsunamis. Scouring at roadways is the primary damage caused by tsunamis; however, tsunami-induced scouring and beach erosion are less understood compared to tsunami runup and tsunami inundation. A set of laboratory experiments are reported in this study on tsunami-induced scour at a road model situated on a sandy beach. Our experiments showed that the distance between the shoreline and a roadway, which varies with tides, was a key factor affecting the scour depth at the road. Having the coastal road at about half of the inundation distance is not the most ideal location. The depth of road embedment did not affect the scour depth in our experiments. It was also found that for typical tsunamis, the scour depth is unlikely to reach its equilibrium stage. The information reported in this study is useful for local authorities to assess potential tsunami damage of roads and to have a better plan for tsunami disaster relief. 相似文献