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1.
BRIAN D. RICKETTS PETER F. BALLANCE BRUCE W. HAYWARD WOLFGANG MAYER 《Sedimentology》1989,36(4):559-580
The abrupt transition from coastal and shallow shelf sediments to bathyal sediments provides a record of rapid subsidence and deepening of the early Miocene Waitemata basin. Basal shallow marine strata (Kawau Subgroup) accumulated upon a highly dissected surface that overlies deformed Mesozoic metagreywacke. The early Miocene coast was characterized by an embayed and cliffed shoreline with numerous sea stacks and islands. Kawau Subgroup lithofacies, which include pocket beach, shallow shelf and base-of-cliff talus deposits, reflect rapidly changing coastline configuration and water depths as the rugged bedrock surface was buried. The response to continued rapid subsidence and transgression in Waitemata basin was a decrease in the supply of coarse clastic sediment. Beach gravels were locally displaced to greater water depths by avalanching down steep bedrock slopes. The first bathyal turbidite facies, which abruptly overlie the shallow-water Kawau Subgroup, include locally derived sediment gravity flows commonly ponded by remnant bedrock submarine highs. When this local supply of sediment had been exhausted, coarse sediment starvation ensued and bathyal muds accumulated. With the resumption of sediment supply and gradual burial of submarine bedrock relief, submarine fans coalesced and increased in lateral extent. Subsidence of the Waitemata basin to bathyal depths is thought to have occurred in less than a million years. From the above hypothesis, a general model of sedimentation is proposed. 相似文献
2.
The paper deals with the analysis of tsunami risks for Western Canada and the numerical modelling of a potential tsunami which
could affect the region and generate significant damage to the western Canadian coastline. Following a review of the seismic
risk and historical tsunamis which occurred along the western Canadian coastline, the authors concluded that this region is
highly vulnerable should a major tsunami occur. Consequently, the authors conducted a study on the numerical modelling of
a possible tsunami generated by movement along the Cascadia fault, which is located offshore British Columbia. The results
of the model outline the significance and extent of the coastal flooding risk associated with such a rare, but destructive
phenomenon. The potential for inundation of the low-lying areas around the coastline of Vancouver Island and in and around
the City of Vancouver was found to be high. A number of recommendations and conclusions focusing on the results of the numerical
simulation are included. 相似文献
3.
Catastrophic tsunami events like those occurred in Papua New Guinea in 1998, Sumatra in 2004 and Japan in 2011, attracted the attention of the scientific community and promoted the development of different tools for assessing tsunami hazard. A preliminary step towards this goal is the knowledge of the events which might affect a specific coastal zone. In this context, we propose a method to identify the tsunami events possibly occurring in areas characterized by scarce data and a non-conservative environment. Accordingly, we propose different indices to summarize the knowledge on tsunami triggering mechanisms (earthquakes, landslides, volcanic eruptions), the characteristics of those mechanisms (magnitude of earthquakes, volume of landslide, Volcanic Explosivity Index) and tsunami features (water height, run-up, wave amplitude, propagation time). This knowledge, considered over a wider area than that of interest, allows for a paramount vision of possible hazardous events that could affect a particular coastal zone. Moreover, the tsunami simulation data and the analysis of potentially tsunamigenic slides which occurred on the Campania continental margins were also considered in the analysis. We focused our attention on Napoli megacity, because the high population density (about 1 million of people live on a territory of 117 km2), together with the presence of active volcanic areas (Ischia, Somma-Vesuvio and Campi Flegrei), make this city potentially exposed to tsunami risk. The main outcome of such an approach shows that in the near field a tsunami amplitude varying from a few centimetres (30–40 cm) to some metres (1–4 m) might be expected at the coastline if the tsunami event was triggered by volcanic activity, whereas no relevant tsunami event should be expected given the peculiar seismicity of the Neapolitan volcanic areas, with earthquakes rarely exceeding 4 Mw, if any possible cascade effects are overlooked. A morphometric analysis of high-resolution bathymetry collected between Ventotene Island and the Gulf of Salerno has shown that the submarine southern sectors of the Ischia Island and the Sorrento Peninsula are characterized by a high density of landslide scars, being thus a potential source area of landslide-generated tsunamis. However, despite the susceptibility of these areas to recurrent slope failures, only four submarine landslide scars were found to be potentially tsunamigenic with estimated tsunami amplitude of few metres at the coastline as predicted by coupling slide morphometry with tsunami amplitude equations. Concerning the tsunamis generated by earthquakes in the Western Mediterranean, only those triggered by high magnitude events (value ≥ 6–7 Mw) might affect the city of Napoli with an amplitude not exceeding 0.5 m, in about 30′. 相似文献
4.
Probabilistic Tsunami Hazard Analysis (PTHA) can be used to evaluate and quantify tsunami hazards for planning of integrated community-level preparedness, including mitigation of casualties and dollar losses, and to study resilient solutions for coastal communities. PTHA can provide several outputs such as the intensity measures (IMs) of the hazard quantified as a function of the recurrence interval of a tsunami event. In this paper, PTHA is developed using a logic tree approach based on numerical modeling for tsunami generated along the Cascadia Subduction Zone. The PTHA is applied to a community on the US Pacific Northwest Coast located in Newport, Oregon. Results of the PTHA are provided for five IMs: inundation depth, flow speed, specific momentum flux, arrival time, and duration of inundation. The first three IMs are predictors of tsunami impact on the natural and built environment, and the last two are useful for tsunami evacuation and immediate response planning. Results for the five IMs are presented as annual exceedance probability for sites within the community along several transects with varying bathymetric and topographic features. Community-level characteristics of spatial distribution of each IM for three recurrence intervals (500, 1000, 2500 year) are provided. Results highlight the different pattern of IMs between land and river transects, and significant magnitude variation of IMs due to complex bathymetry and topographic conditions at the various recurrence intervals. IMs show relatively higher magnitudes near the coastline, at the low elevation regions, and at the harbor channel. In addition, results indicate a positive correlation between inundation depth and other IMs near the coastline, but a weaker correlation at inland locations. Values of the Froude number ranged 0.1–1.0 over the inland inundation area. In general, the results in this study highlight the spatial differences in IMs and suggest the need to include multiple IMs for resilience planning for a coastal community subjected to tsunami hazards. 相似文献
5.
Kapila Dahanayake Nayomi Kulasena G. V. Ravi Prasad Koushik Dutta D. K. Ray 《Natural Hazards》2012,63(1):197-209
After the 2004 Sumatra?CAndaman tsunamigenic earthquake, waters from the ocean moved upstream along rivers, bays, harbors, and lagoons and inundated many coastal and inland locations in the southern, eastern, and northern parts of Sri Lanka. The tsunami waters were observed to move upwards inland and then recede downwards to the ocean after varying inundation periods in different coastal areas. Subsequent massive tsunami waves came with the wave height varying from 3 to 8?m inland with speed of about 30?C40?kmph. The oceanic waves carrying heterogeneous sediments with water deposited them in coastal as well as inland locations about 1?km from the present coastline. Given the chaotic nature of tsunami oceanic waves, pre-tsunami deposits, such as beach sands, debris from coral reefs and buildings, parts of vehicles and ships, and tree trunks are found incorporated in authentic tsunami sediments. Thus, the texture, structure, and composition of sediments deposited by tsunami waters differed from one location to another. Therefore, in identifying paleo-tsunami sediments, care was taken to compare them with diagnostic unmixed uncontaminated recent tsunami sediments having characteristic textures and marine microfossil assemblages, such as foraminifera, radiolarians, and diatoms where preserved in coastal depressions. The radiocarbon ages of the carbonate and the organic fractions of these sediments are stratigraphically inconsistent, indicating mixing of sediments by the tsunami waves. The concentrations of organic carbon and nitrogen and their isotopic signatures confirm marine origin of these sediments. 相似文献
6.
Prognostic characteristics of tsunamis in the East (Japan) Sea based on numerical simulations are investigated by using linear
long wave theory. Due to the lack of observed data, the concept of the synthetic catalogue is applied to generate possible
tsunami scenarios. It includes four real events that occurred in the East (Japan) Sea during the 20th century, 24 hypothetical
tsunamigenic earthquakes located in the gap zones of the seismic map, and 76 idealized model ‘hydrodynamic’ sources covering
the eastern part of the East (Japan) Sea uniformly. The tsunami wave height distributions along the East (Japan) Sea coastline
due to these hypothetical events are computed. From the geographical distributions of tsunami wave height for all possible
events, it is found that there exist several coastal locations where the tsunami risk is relatively lower than in other zones.
The relation between the maximal value of the tsunami height and its average value is analyzed. It is found that the maximal
tsunami height does not exceed the mean wave height times a constant. The uniform bounded curve for all areas can be obtained
if the mean wave height is replaced by the modified mean wave height (1/3 of largest waves). The problem of quantitative definition
of the prognostic tsunami wave height for each location based on the data from the synthetic catalogue is discussed. The results
of tsunami wave height analysis based on the synthetic catalogue can be used as a tool for coastal disaster mitigation planning. 相似文献
7.
Land subsidence caused by ground water withdrawal in urban areas 总被引：1，自引：0，他引：1
At least eight urban areas in the world have encountered significant economic impact from land subsidence caused by pumping of ground water from unconsolidated sediment. The areas, most of which are coastal, include Bangkok, Houston, Mexico City, Osaka, San Jose, Shanghai, Tokyo, and Venice. Flooding related to decreased ground elevation is the principal adverse effect of the subsidence. Lesser effects include regional tilting, well-casing failures, rising buildings, and ground failure or rupture. Subsidence of most of these urban areas began before the phenomenon was discovered and understood. Thus, the subsidence problems were unanticipated. Methods to arrest subsidence typically have included control of ground water pumping and development of surface water to offset the reductions of ground water pumping. Ground water recharge has also been practiced. Areas threatened by flooding have been protected by extensive networks of dikes and sea walls, locks, and pumping stations to remove storm runoff. 相似文献
8.
The sandy deposits produced by tsunamis and liquefaction share many sedimentary features, and distinctions between the two are important in seismically active coastal zones. Both types of deposits are present in the wetlands bordering Puget Sound, where one or more earthquakes about 1100 years ago caused both tsunami flooding and sediment venting. This co‐occurrence allows an examination of the resulting deposits and a comparison with tsunami and liquefaction features of modern events. Vented sediments occur at four of five wetland field localities and tsunami deposits at two. In comparison with tsunami deposits, vented sediments in this study and from other studies tend to be thicker (although they can be thin). Vented sediments also have more variable thickness at both outcrop and map scale, are associated with injected dykes and contain clasts derived from underlying deposits. Further, vented sediments tend to contain a greater variety of sedimentary structures, and these structures vary laterally over metres. Tsunami deposits compared with vented sediments are commonly thinner, fine and thin landward more consistently, have more uniform thickness on outcrop and map scales, and have the potential of containing coarser clasts, up to boulders. For both tsunami deposits and vented sediments, the availability and grain size of source material condition the characteristics of the deposit. In the cases presented in this paper, both foraminifera and diatom assemblages within tsunami deposits and vented sediments consisted of brackish and marine species, and no distinction between processes could be made based on microfossils. In summary, this study indicates a need for more careful analysis and mapping of coastal sediments associated with earthquakes to avoid misidentification of processes and misevaluation of hazards. 相似文献
9.
Distribution and sedimentary characteristics of tsunami deposits along the Cascadia margin of western North America 总被引：1，自引：0，他引：1
Tsunami deposits have been found at more than 60 sites along the Cascadia margin of Western North America, and here we review and synthesize their distribution and sedimentary characteristics based on the published record. Cascadia tsunami deposits are best preserved, and most easily identified, in low-energy coastal environments such as tidal marshes, back-barrier marshes and coastal lakes where they occur as anomalous layers of sand within peat and mud. They extend up to a kilometer inland in open coastal settings and several kilometers up river valleys. They are distinguished from other sediments by a combination of sedimentary character and stratigraphic context. Recurrence intervals range from 300–1000 years with an average of 500–600 years. The tsunami deposits have been used to help evaluate and mitigate tsunami hazards in Cascadia. They show that the Cascadia subduction zone is prone to great earthquakes that generate large tsunamis. The inclusion of tsunami deposits on inundation maps, used in conjunction with results from inundation models, allows a more accurate assessment of areas subject to tsunami inundation. The application of sediment transport models can help estimate tsunami flow velocity and wave height, parameters which are necessary to help establish evacuation routes and plan development in tsunami prone areas. 相似文献
10.
The Holocene Storegga Slide tsunami in the United Kingdom 总被引：1，自引：0，他引：1
D. E. Smith S. Shi R. A. Cullingford A. G. Dawson S. Dawson C. R. Firth I. D. L. Foster P. T. Fretwell B. A. Haggart L. K. Holloway D. Long 《Quaternary Science Reviews》2004,23(23-24):2291-2321
All currently known sites in the United Kingdom with evidence for the Holocene Storegga Slide tsunami are described. Information on the altitude, distribution, stratigraphical context, age, particle size profile and microfossil characteristics of the deposits is presented. The tsunami involved a greater area than previously described, reaching a coastline over 600 km long. The ubiquitous sand layer which forms the main deposit associated with the event is shown to exhibit a consistent morphology and a particle size profile marked by fining-upwards sequences. An analysis of new and previously published radiocarbon dates indicates that from evidence in the United Kingdom, the event took place sometime around 7100 radiocarbon years BP (7900 calibrated years BP). A new isobase model for mainland Scotland and adjacent areas, providing a preliminary estimate of land uplift since the tsunami, is presented. The model estimates contemporary sea surface level offshore at 14 m below the present day mean high water spring tides. Tsunami sediment run-up is greatest in inlets, where it reaches at least 25 m on Shetland and at least 5 m along the mainland coastline to the south, and run-up of the tsunami would have exceeded these values. The tsunami sediments identified here are considered particularly valuable as a synchronous marker horizon. 相似文献
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12.
The occurrence of land subsidence in the Kingdom Saudi Arabia is either natural or man-made. Natural land subsidence occurs due to the development of subterranean voids by a solution of host rocks in carbonate and evaporite terrains, over many areas of Saudi Arabia. Man-induced land subsidence is either due to the removal of groundwater in the agricultural areas or to wetting of unstable soils. Therefore, earth fissures and a lowering of the ground surface in unconsolidated sediments took place in alluvial plains and volcanic vent terrains. Unstable soils include Sabkha soils and loess sediments. These types of soils occur in coastal plains, desert areas and volcanic terrains. When this soil is wetted either during agricultural activities, waste disposal or even during a rain storm, subsidence takes place due to either the removal of salts from the Sabkha soil or the rearrangement of soil particles in loess sediments. 相似文献
13.
中国东海、南海等近海临近琉球海沟、马尼拉海沟等俯冲带,地震频发。过去的海啸研究主要关注历史文献分析、海啸数值模拟等,据此评估中国近岸海啸灾害的历史和风险。历史时期是否引发了海啸,特别是具有特大致灾风险的大海啸记录,目前还不明确。近年来,本课题组通过对海岛、海洋沉积和海岸带及其岛屿的沉积过程、海啸遗迹和历史记录研究,阐述了确定古海啸的系列研究方法。首先通过对南海西沙群岛东岛湖泊沉积序列、大量砗磲和珊瑚块在海岛分布的特征分析,识别出距今千年的一次海啸事件。以此为标志,根据湖泊沉积结构作为识别海岛海啸沉积的特征。同时提出了确定海岛海啸发生时代的样品采集和定年方法,其中包括根据事件沉积层顶部和底部植物残体14C年龄定年和历史文献记录的印证。首次确定在过去1 300年中,南海发生过一次海啸,其发生时间为公元1076年。为了寻找更古老的海啸记录,结合对东海闽浙沿岸过去两千年海洋泥质沉积的分析,发现南海海啸在沉积序列中留下记录,但除此之外沉积记录中并无更强的扰动,因此东海在过去两千年中受到海啸的影响较小。1076年的海啸同时冲击了南海沿岸,通过对广东南澳岛考察发现,岛屿东南海岸保存着距今约1 000年的海啸沉积层,其中夹杂着宋代陶器瓷器残片。对遗迹数量变化的分析显示,岛上的文化受海啸破坏出现了长达500年的文化中断,直至明代中后期设镇之后才逐渐恢复。根据海啸层植物残体、贝壳14C测年、覆盖海啸层的海砂光释光定年以及瓷器碎片的年代鉴定了海啸的发生时代,并据此提出了海岸带古海啸沉积的定年方法。此外,不同环境下海啸沉积的特征也存在较大区别,需要结合地形、沉积物来源以及地球化学特征等多种指标进行识别。有迹象表明海南岛东侧海岸带有海啸破坏的明显证据,需要进行深入的研究。 相似文献
14.
Several areas of Nakuru Town and its environs often undergo subsidence along the parallel fault zones during and after heavy
rainfall. During the rainy season, when most of the subsidence occurs, the overlying unconsolidated volcanoclastic sediments
become oversaturated with water. The water reduces the shear strength of the sediments and also introduces extra loading through
saturation leading to subterranean erosion along faults. The unconsolidated sediments then collapse into the subsurface water
channels which closely follow the fault zones, leading to formation of “sinkholes”. The frequent incidences of ground subsidence
in the study area, have caused several fatalities, destroyed settlements and physical infrastructure. Furthermore persistent
subsidence has increased the cost of construction and the repair of the destroyed properties. Apart from being hazardous,
ground subsidence degrades environment when sewage water, refuse and garbage enter into the groundwater systems through the
sinkholes. The fissures formed after subsidence also stand prominently as ugly features from the rest of the terrain. Mitigation
measures including control, channelizing of drainage, proper engineering practices and appropriate land use are suggested
in this paper.
Received: 1 December 1998 · Accepted: 8 March 1999 相似文献
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16.
Alfred Uchman Markes E. Johnson Ricardo S. Ramalho Rui Quartau Björn Berning Ana Hipólito Carlos S. Melo ANA C. Rebelo Ricardo Cordeiro Sérgio P. Ávila 《Sedimentology》2020,67(7):3595-3618
Sedimentary rocks are rarely preserved on reefless volcanic oceanic islands because their sediments are mostly exported from coastal areas towards the deep sea and such islands typically undergo subsidence. In contrast, the exceptional geological record of the uplifted Santa Maria Island (Azores) provides a unique opportunity to gain insight on such coastal systems. This study focuses on a locality at Ponta do Cedro (eastern Santa Maria Island), which features a series of marine fossiliferous sediments wedged between steep lava deltas. As demonstrated by local structure, these sediments correspond to clinoforms deposited on the steep submarine slope of an active volcanic island, implying transport from shallow waters to greater depths and subsequent colonization by benthic communities. Rapid volcanic progradation eventually sealed the deposits, allowing for their preservation and providing a rare snapshot of the ecology during those intervals, in addition to insights on sedimentary dynamics along submarine island slopes. This study reveals spatial relationships between wedges of sedimentary bodies encapsulated by lavas in the Ponta do Cedro section, and interprets depositional processes preserved in those strata based on sedimentological and palaeontological data. The dynamics of the environment are mostly related to relative sea-level changes, intense volcanic activity and regional uplift during the Neogene. 相似文献
17.
Kick'em Jenny is a submarine volcano situated 9 kilometres north of Grenada in the Lesser Antilles. A preliminary study suggests that the volcano is a prime candidate for tsunamigenic eruptions on a potentially hazardous scale, possibly affecting the whole of the Eastern Caribbean region. The uniqueness of individual volcanic eruptions means that attempts to generalise tsunamigenic mechanisms are extremely tentative. However, the theory of underwater explosion generated water waves is applicable to submarine volcanoes to model explosive eruptions. Using this theory, initial maximum ocean surface displacements are calculated for Kick'em Jenny hydroeruptions, corresponding to various event magnitudes (up to a worst-case scenario eruption on the scale of Krakatau, 1883). Wave propagation theories are then applied to the resulting tsunami wave dispersion, before beach shoaling equations are used to estimate the maximum tsunami run-up at adjacent coastal areas. Maps of the region have been prepared showing the paths of the wave-fronts (ray-tracing), travel times and maximum wave run-up amplitudes along coastlines. Finally, an attempt is made to assess how great a hazard the volcano represents, by considering the probability of each magnitude event occurring. 相似文献
18.
《International Geology Review》2012,54(3):336-355
This paper begins with a discussion of the geologic structure and origin of the Caspian depression, describes the history of changes in level of the Caspian, and the different terrace levels formed by these changes. Next the stratigraphy and structure of the complex Azerbaijan coastal area are covered. Composition of the sediments brought in by the various rivers is strongly affected by climate, e. g. , the Volga and Ural bring in much dissolved carbonate from the black-earth soils. A small amount of windblown material is contributed. Fluctuations in level of the sea, consequently its salinity, are mainly influenced by discharge of the Volga. Chemistry of the Caspian is discussed; it is everywhere oversaturated with respect to calcium carbonate and greatest salinities are attained on the eastern side. All waters contain oxygen except the deepest holes, for circulation reaches the bottom almost everywhere, consequently sediments are greenish gray, not black. Regional variation in phosphate and silica content are also discussed briefly. In the vicinity of Cape Apsheron, submarine erosion takes place on highs, while hollows are filled in with sediment. Sediments are classified and mapped on the basis of percentage finer than 0.01 mm, and the amount of this material correlates in general with depth of water. Sediments in areas of submarine erosion often show bimodal histograms. The microfauna consists largely of Rotalia and ostracods, but many reworked Foraminifera are found; fauna of the deltas are contrasted with those of the open Caspian. Some shallow water forms have been transported into deeper water by “coastal suspensions.” Heavy minerals along the Caspian coast are complex, and reflect local source areas. Triangular diagrams are used to show variations in mineral percentages, and to recognize specific sources. Chemical analyses of the sediments show calcium carbonate most abundant in the east. Manganese content increases with amount of fines, and both phosphorus and manganese increase in the deepest parts and near large river mouths. Details on the changes of chemical composition with grain size, location, etc. , are used to propose a marine coastal origin for the “Productive Stratum” in Azerbaijan.—R. L. Folk 相似文献
19.
A detailed assessment of the impact of a far-field tsunami on the Australian coastline was carried out in the Steep Point
region of Western Australia following the July 17 2006 Java tsunami. Tsunami inundation and run-up were mapped on the basis
of eyewitness accounts, debris lines, vegetation damage and the occurrence of recently deposited fish, starfish, corals and
sea urchins well above high-tide mark. A topographic survey using kinematic GPS with accuracies of 0.02 m in the horizontal
and 0.04 m in the vertical recorded flow depths of between 1 and 2 m, inundation of up to 200 m inland, and a maximum recorded
run-up of 7.9 m AHD (Australian Height Datum). The tsunami impacted the sparsely populated Steep Point coastline close to
low tide. It caused widespread erosion in the littoral zone, extensive vegetation damage and destroyed several campsites.
Eyewitnesses reported three waves in the tsunami wave train, the second being the largest. A sand sheet, up to 14 cm thick
and tapering landwards over 200 m, was deposited over coastal dunes. The deposits are predominantly composed of moderately
well-sorted, medium-grained carbonate sand with some gravel and organic debris. A basal unconformity defines the boundary
between tsunami sediments and underlying aeolian dune sand. Evidence for up to three individual waves is preserved as normally
graded sequences mantled by layers of dark grey, organic-rich fine silty sand. Given the strong wind regimes in the area and
the similarity of the underlying dune deposits to the tsunami sediments, it is likely that seasonal erosion will remove all
traces of these sediment sheets within years to decades. 相似文献
20.
For centuries, inhabitants of coastal areas have suffered from the effects of tsunamis. Turkey, with a coastline of 8333 km, has experienced many tsunamis.Historical records reveal that, during the observation period over 3000 years, the coastal and surrounding areas of Turkey have been affected by more than ninety tsunamis. These tended to cluster around the Marmara Sea, the city of Istanbul and the gulfs of Izmit, Izmir, Fethiye and Iskenderun. Each of the tsunami occurrences surveyed in this paper deserves further individual study. The most extensive available information concerns the tsunamis associated with the Istanbul Earthquakes of 1509 and 1894, the Eastern Marmara Earthquake in 1963 and that of Izmit in 1999,which disturbed the Marmara Sea; the Earthquake of 1939 in Erzincan ineastern Anatolia; and the 1968 Bartn Earthquake, which affected Fatsa and Amasra on the Black Sea. In addition to these, it is known that a tsunami occurred in 1598 on the shores of the Black Sea in connection with an earthquake at Amasya in northern Anatolia. 相似文献