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1.
Aliki lagoon is a small lagoon located on the micro-tidal south coast of the Gulf of Corinth, Greece. The sediments of the lagoon recovered in three cores provide a record of late Holocene environmental change, including tectonic subsidence, tsunami layers, and change in local vegetation and sedimentation. Four periods of rapid environmental changes were identified over a 5000-yr-long record. These date from about 4700, 3000, 2500 and 2000 yr BP. Each change is linked to activity on the Egion fault, a deepening of the lagoonal bottom and a rise in relative sea level. Six tsunami events are recorded and have been caused by earthquakes on the Egion fault (three events ∼4700, ∼3000 and ∼2500 BP), Eliki fault (2350±40 yr BP) and two more distal fault ruptures. The vegetation history and pollen zones are similar to those recognised by Jahns (Vegetation Hist. Archaebot. 2 (1993) 187) on the Argive Plain, 100 km southeast of the lagoon. Five successive sedimentological configurations are established in relation to the time frame provided by the tectonic activity: (1) crevasse splay; (2) fresh to brackish water marsh; (3) and (4) brackish to hypersaline “blind” lagoon, and (5) brackish to hypersaline “blind” lagoon or brackish open lagoon.  相似文献   

2.
The western Peloponnese was repeatedly hit by major tsunami impacts during historical times as reported by historical accounts and recorded in earthquake and tsunami catalogues. Geological signatures of past tsunami impacts have also been found in many coastal geological archives. During the past years, abundant geomorphological and sedimentary evidence of repeated Holocene tsunami landfall was found between Cape Katakolo and the city of Kyparissia. Moreover, neotectonic studies revealed strong crust uplift along regional faults with amounts of uplift between 13 m and 30 m since the mid-Holocene. This study focuses on the potential of direct push in situ sensing techniques to detect tsunami sediments along the Gulf of Kyparissia. Direct push measurements were conducted on the landward shores of the Kaiafa Lagoon and the former Mouria Lagoon from which sedimentary and microfaunal evidence for tsunami landfall are already known. Direct push methods helped to decipher in situ high-resolution stratigraphic records of allochthonous sand sheets that are used to document different kinds of sedimentological and geomorphological characteristics of high-energy inundation, such as abrupt increases in grain size, integration of muddy rip-up clasts and fining upward sequences which are representative of different tsunami inundation pulses. These investigations were completed by sediment coring as a base for local calibration of geophysical direct push parameters. Surface-based electrical resistivity tomography and seismic data with highly resolved vertical direct push datasets and sediment core data were all coupled in order to improve the quality of the geophysical models. Details of this methodological approach, new in palaeotsunami research, are presented and discussed, especially with respect to the question of how the obtained results may help to facilitate tracing tsunami signatures in the sedimentary record and deciphering geomorphological characteristics of past tsunami inundation. Using direct push techniques and based on sedimentary data, sedimentary signatures of two young tsunami impacts that hit the Kaiafa Lagoon were detected. Radiocarbon age control allowed the identification of these tsunami layers as candidates for the ad 551 and ad 1303 earthquake and tsunami events. For these events, there is reliable historical data on major damage on infrastructure in western Greece and on the Peloponnese. At the former Mouria Lagoon, corroborating tsunami traces were found; however, in this case it is difficult to decide whether these signatures were caused by the ad 551 or the ad 1303 event.  相似文献   

3.
Sue Dawson   《Sedimentary Geology》2007,200(3-4):328-335
Distinctive diatom assemblages may be associated with tsunami sediments and may often contrast with the assemblages found within sediments underlying the tsunami deposit as well as those associated with the modern coastal environment. Sediments associated with the 1998 tsunami that destroyed much of the Sissano lagoon area in northern Papua New Guinea have been investigated. Surface sediments from three transects across the sediment spit near Warapu have been examined for diatom content and preservation. The preservation is variable, and the data show an, often chaotic, assemblage that can be attributed to the tsunami waves incorporating and depositing diatoms from distinctive habitat zones during their runup and subsequent backwash. The diatoms identified within the Warapu sediments indicate an origin from within the inter-tidal and offshore area rather than from the beach–sand spit complex. The sand deposits disclose a high percentage, in excess of 75%, of broken diatom valves, and a predominance of centric (circular) species due to preferential preservation. The study demonstrates that the application of diatom biostratigraphy to modern tsunami deposits can be used in conjunction with other stratigraphical lines of evidence to interpret the source and provenance of historical and palaeo-tsunami deposits.  相似文献   

4.
Shinozaki  Tetsuya  Sawai  Yuki  Ito  Kazumi  Hara  Junko  Matsumoto  Dan  Tanigawa  Koichiro  Pilarczyk  Jessica E. 《Natural Hazards》2020,103(1):713-730

Geological evidence of recent tsunamis from sediment samples collected from Lake Tokotan, a coastal lagoon in eastern Hokkaido, northern Japan, was detected using computed tomography (CT) and soft X-ray images, grain size, and radionuclide profiles. Initial field observations revealed that sediments had no discernable sedimentary structures at the top of the core. However, results of CT imaging, soft X-ray, and grain size analyses show evidence for three invisible sand layers that are intercalated with mud layers. These sand layers exhibit trends of landward fining and thinning. Furthermore, the distribution of sand layers was limited to the center and seaward parts of the lake. Vertical profiles of cesium and lead concentrations in combination with recent eyewitness accounts indicated that these sand layers are correlated with the 1973 Nemuro-oki, 1960 Chilean, and 1952 Tokachi-oki tsunami events. The deeper part of the sediment cores includes three volcanic ash layers and three prehistoric coarse sand layers. The prehistoric layers are correlated with unusually large tsunamis that were geologically identified in previous studies from eastern Hokkaido. These findings suggest that nondestructive techniques, in combination with radionuclide analysis, allow for detection of frequent but faint tsunami deposits. This technique allows for an improved understanding of the history of tsunami inundation in Lake Tokotan and of other locations for which stratigraphic evidence for faint tsunamis layers is not readily apparent from field assessments.

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5.
Tsunami are one of the major natural hazards in the Caribbean. The historical record lists 88 tsunami, from local events to teletsunami, in the time period from 1489 to 1998. This study focuses on the spatial distribution and geomorphologic evidence related to coarse littoral sediment and boulder deposition by tsunami events of Holocene age in the Southern Caribbean. At a worldwide scale, these debris deposits represent the most extensive and impressive records of Holocene paleo-tsunami so far studied. Hitherto, the Leeward Lesser Antilles, consisting of the islands of Aruba, Curaçao and Bonaire, were not known to have had tsunami affecting their coastlines. The possible contribution of tsunami to configuring coastlines (e.g. the questions of embayment development, the coastal environment changes, and the absence of Holocene fringing reefs along the windward coasts) is discussed.  相似文献   

6.
The December 26, 2004 Indian Ocean tsunami was one of the largest in human history, devastating the coastal wetlands of surrounding countries. This study present the chemical analyses of tsunamigenic and pre-tsunami sediments from Hikkaduwa and Hambantota lagoons in southern Sri Lanka, to assess their geochemical composition, their source, and subsequent environmental impacts. Principal component analysis of the tsunami sediments shows that 42% of the total variance is accounted for calcium oxide and Sr. That is, the tsunami deposits are rich in biogenic phases derived from shallow marine sediments. High organic matter contents of the tsunami sediments of up to 80 wt% also support this interpretation. The association of chlorine (<9.4 wt%), brome (<170?mg/kg), arsenic (<17?mg/kg), iron (III) oxide (<12.9 wt%) and sulfur (<7.6 wt%) accounts for 33% of the variance, reflecting higher salinity. This further suggests that the sediments were mainly derived from a marine environment, rather than from non-marine sands and/or soils. Immobile element contents and relations (thorium, scandium and zirconium) suggest that the tsunami sediment source was mostly felsic in composition, with some mafic component, and mixed with predominantly shallow marine shelf or slope sediments. Additional compositional variations in the tsunami sediments in both lagoons may be associated with variations of wave strength along the coast and by the morphology of the continental shelf. Lower elemental abundances in Hambantota lagoon sediments compared to Hikkaduwa equivalents may thus reflect a greater non-marine component in the former, and greater shelf sediment component in the latter.  相似文献   

7.
Flexure of the lithosphere and continental margin basins   总被引:4,自引:0,他引:4  
The accumulation of sediments at an Atlantic-type continental margin constitutes a load on the lithosphere which simply sags due to its weight. Studies of the geometry of deformation suggests the lithosphere will respond to these loads either by local loading of an Airy-type crust or flexural loading of a strong rigid crust. Sediment loading models of either type cannot, however, explain the substantial thicknesses of shallow-water sediments observed in commercial boreholes from Atlantic-type margins. Other factors such as thermal contraction, gravitational outflow of crustal material or deep crustal metamorphism may contribute to the subsidence. We have used biostratigraphic data from commercial boreholes from the Gulf of Lion and the East Coast U.S.A. to quantitatively determine the contribution of sediment loading to the subsidence. From these data we determined sea-floor and basement depths for sequential time intervals during margin development. Using the sediment loading models the sediment layers at each margin were progressively “backstripped” and the depth basement would have been without the sediment load calculated. The computed basement depths indicate there is a recognizable component of the subsidence of these margins which is caused by processes other than adjustments to the weight of the sediment. The nature of this subsidence is discussed and comparisons are made with that which would be expected from thermal-contraction models.  相似文献   

8.
The Darwinian progressive subsidence model for the evolution of fringing reefs, barrier reefs and atolls has been generally accepted following the indisputable proof of subsidence provided by drilling results in the Pacific. Nonetheless, there are data that do not fit the expectations of the model, such as the similar lagoon depths of barrier reefs and atolls as opposed to the subsidence theory’s implicit prediction that atolls should have significantly greater depths. In contrast, a great deal of evidence supports the influence of meteoric solution on barrier reef morphology. For example, the maximum lagoon depth of 56 modern barrier reefs is statistically correlated with the lagoon catchment area for modern annual rainfall. These modern rainfall patterns would seem to be a reasonable proxy for relative geographic differences in glacial lowstand rainfall, even though the absolute amounts of such rainfall are unknown. The correlation therefore suggests the importance of Pleistocene subaerial solution in contributing to barrier reef morphology. Further support for antecedent influence occurs in the form of barrier reef passes in which the depth of the reef pass is correlated with onshore drainage volumes. On a larger scale, the Cook Island of Mangaia provides evidence that solution can produce barrier reef morphology independent of reef development. In contrast, there are no examples of the subsidence-predicted lagoon transition of fringing reefs to barrier reefs to atolls. Moreover, the common occurrence of fringing reefs within barrier reefs negates subsidence as a causal factor in their ‘presumed progressive evolutionary development. Consequently, the evidence to date suggests that a solution morphology template has been accentuated by reef construction to produce the diagnostic barrier reef morphology we see today. The importance of subsidence would seem to be in accounting for the overall thickness of the resulting carbonate caps of oceanic examples and in contributing to lagoon depth variation among the larger continental entities.
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9.
10.
A simple model for calculating tsunami flow speed from tsunami deposits   总被引:2,自引:0,他引:2  
This paper presents a simple model for tsunami sedimentation that can be applied to calculate tsunami flow speed from the thickness and grain size of a tsunami deposit (the inverse problem). For sandy tsunami deposits where grain size and thickness vary gradually in the direction of transport, tsunami sediment transport is modeled as a steady, spatially uniform process. The amount of sediment in suspension is assumed to be in equilibrium with the steady portion of the long period, slowing varying uprush portion of the tsunami. Spatial flow deceleration is assumed to be small and not to contribute significantly to the tsunami deposit. Tsunami deposits are formed from sediment settling from the water column when flow speeds on land go to zero everywhere at the time of maximum tsunami inundation. There is little erosion of the deposit by return flow because it is a slow flow and is concentrated in topographic lows. Variations in grain size of the deposit are found to have more effect on calculated tsunami flow speed than deposit thickness. The model is tested using field data collected at Arop, Papua New Guinea soon after the 1998 tsunami. Speed estimates of 14 m/s at 200 m inland from the shoreline compare favorably with those from a 1-D inundation model and from application of Bernoulli's principle to water levels on buildings left standing after the tsunami. As evidence that the model is applicable to some sandy tsunami deposits, the model reproduces the observed normal grading and vertical variation in sorting and skewness of a deposit formed by the 1998 tsunami.  相似文献   

11.
A case study was conducted for the Thailand Khao Lak coast using a forward numerical model to understand uncertainties associated with interpreting tsunami deposits and relating them to their tsunami sources. We examined possible effects of the characteristics of tsunami source, multiple waves, sediment supply and local land usages. Numerical results showed that tsunami-deposit extent and thickness could be indicative of the slip value in the source earthquake near the surveyed coastal locations, provided that the sediment supply is unlimited and all the deposits are well preserved. Deposit thickness was found to be largely controlled by the local topography and could be easily modified by backwash flows or subsequent tsunami flows. Between deposit extent and deposit thickness, using deposit extent to interpret the characteristics of a tsunami source is preferable. The changing of land usages between two tsunami events could be another important factor that can significantly alter deposit thickness. There is a need to develop inversion models based on tsunami heights and/or run-up data for studying paleotsunamis.  相似文献   

12.
Co-seismic phenomena along the south coastline included liquefaction, subsidenceand tsunami. Construction on areas composed of fluvial and alluvial sediments aswell as unconsolidated fill increased the risk by creating potential for amplificationof seismic waves. Cyclic mobility liquefaction was common along the coastline, andlevel-ground liquefaction was observed. Flow liquefaction is held forth as a possibilityin the Deirmendere submarine landslide. Damage to structures was markedly more in areas of unconsolidated sediments. One or more tsunami struck immediately after the event; the uniformity of tsunami impact indicating a wave coming from 310° suggests that submarine faulting was the major source of tsunami. Over 800,000 m2 of subsidence resulted from sediment slumping, fault controlled subsidence, and possibly post-liquefaction sediment compaction. After a brief period of post-event abandonment, reclamation and use of coastal areas is well underway. This creates a tension between human desires pushing for quick and inexpensive re-inhabitation of the coastal areas, and the needs for zoning and building codes for risk reduction. In this high-risk area suchcontrary cultural mandates cannot yield ideal results. It is suggested that an alternativemodel of immediate post-event creation of parks and natural areas that would yield benefit is preferable in coastal areas rather than the enforcement approach currently favored.  相似文献   

13.
According to various historical sources an earthquake and an associated tsunami wiped out the Greek city of Helike on the Gulf of Corinth in 373 B.C. This study combines stratigraphical data from a new series of sediment cores with archaeological findings of the Helike Project to better assess the fate of Helike. Abrupt lithological changes, for example, from coarse‐grained littoral facies at the base to fine‐grained lagoonal deposits, in three of the new cores suggest sudden formation of lagoonal or lacustrine conditions in the central delta during tectonic events of subsidence due to fault‐slip. These events date before c. 2550 B.C., before 348 cal. B.C.–64 cal. A.D. (probably 373 B.C.), and before 1437–1634 cal. A.D. (probably A.D. 1402). Vertically displaced isochronic surfaces between two neighboring cores may be related to active faulting of the fan‐delta north of the Western Helike Fault Zone in 373 B.C. and A.D. 1402. Although the Helike Project reported possible tsunami evidence in earlier cores and trenches, no unequivocal sedimentary traces of a tsunami were identified in the Classical horizons of the new cores.  相似文献   

14.
15.
Coastal communities in the western United States face risks of inundation by distant tsunamis that propagate across the Pacific Ocean as well as local tsunamis produced by great (Mw?>?8) earthquakes on the Cascadia subduction zone. In 1964, the Mw 9.2 Alaska earthquake launched a Pacific-wide tsunami that flooded Cannon Beach, a small community (population 1640) in northwestern Oregon, causing over $230,000 in damages. However, since the giant 2004 Indian Ocean tsunami, the 2010 Chile tsunami and the recent 2011 Tohoku-Oki tsunami, renewed concern over potential impacts of a Cascadia tsunami on the western US has motivated closer examination of the local hazard. This study applies a simple sediment transport model to reconstruct the flow speed of the most recent Cascadia tsunami that flooded the region in 1700 using the thickness and grain size of sand layers deposited by the waves. Sedimentary properties of sand from the 1700 tsunami deposit provide model inputs. The sediment transport model calculates tsunami flow speed from the shear velocity required to suspend the quantity and grain size distribution of the observed sand layers. The model assumes a steady, spatially uniform tsunami flow and that sand settles out of suspension forming a deposit when the flow velocity decreases to zero. Using flow depths constrained by numerical tsunami simulations for Cannon Beach, the sediment transport model calculated flow speeds of 6.5?C7.6?m/s for sites within 0.6?km of the beach and higher flow speeds (~8.8?m/s) for sites 0.8?C1.2?km inland. Flow speed calculated for sites within 0.6?km of the beach compare well with maximum velocities estimated for the largest tsunami simulation. The higher flow speeds calculated for the two sites furthest landward contrast with much lower maximum velocities (<3.8?m/s) predicted by numerical simulations. Grain size distributions of sand layers from the most distal sites are inconsistent with deposition from sediment falling out of suspension. We infer that rapid deceleration in tsunami flow and convergences in sediment transport formed unusually thick deposits. Consequently, higher flow speeds calculated by the sediment model probably overestimate the actual wave speed at sites furthest inland.  相似文献   

16.
The widespread sheets of fine particulate sediment frequently deposited by tsunami constitute valuable evidence from which to reconstruct tsunami inundation. This is illustrated with evidence from three sites near Montrose, in eastern Scotland, U.K., where a horizon of mainly sand, laid down during the Holocene Storegga Slide palaeotsunami of circa 8000 BP is examined. The horizon is remarkably consistent in its distribution, morphology, stratigraphy, and particle size characteristics. These properties allow inferences to be made on the nature of tsunami flow onshore and run-up. It is suggested that estimates can be made of the possible depth of water involved from the characteristics of the sediment, and thus of the extent of inundation involved in the tsunami at these sites.  相似文献   

17.
De Lange  W. P.  Healy  T. R. 《Natural Hazards》2001,24(3):267-284
The Hauraki Gulf is a semi-enclosed sea next to the largest population centre in New Zealand, the Auckland metropolitan region. The potential tsunami hazard is of concern to regional and local planners around the Hauraki Gulf. The Hauraki Gulf has recorded 11 tsunamis and one meteorological tsunami (rissaga) since 1840.The historical tsunami data are relatively sparse, particularly for the largest events in 1868 and 1883. Moreover, local sources may produce damaging tsunamis but none has occurred during recorded history. Therefore numerical modelling of potential tsunami events provides a powerful tool to obtain data for planning purposes. Three main scenarios have been identified for numerical modelling:1. A teletsunami event from an earthquake off the West Coast of South America. Historically this region has produced the largest teletsunamis in the Hauraki Gulf.2. A tsunami generated by a local earthquake along the Kerepehi Fault. This fault bisects the Gulf, has been active during the last century at the southern inland end, and is overlain by a considerable thickness of soft sediment that may amplify the seismic waves.3. A tsunami generated by a volcanic eruption within the Auckland Volcanic Field. This field has involved a series of mainly monogenetic basaltic eruptions over the last 140,000 years. Many of these eruptions have involved phreatomagmatic eruptions around the coastal margins, or within the shallow waters close to Auckland.  相似文献   

18.
Modern subaerial sand beds deposited by major tsunamis and hurricanes were compared at trench, transect, and sub-regional spatial scales to evaluate which attributes are most useful for distinguishing the two types of deposits. Physical criteria that may be diagnostic include: sediment composition, textures and grading, types and organization of stratification, thickness, geometry, and landscape conformity.

Published reports of Pacific Ocean tsunami impacts and our field observations suggest that sandy tsunami deposits are generally < 25 cm thick, extend hundreds of meters inland from the beach, and fill microtopography but generally conform to the antecedent landscape. They commonly are a single homogeneous bed that is normally graded overall, or that consists of only a few thin layers. Mud intraclasts and mud laminae within the deposit are strong evidence of tsunami deposition. Twig orientation or other indicators of return flow during bed aggradation are also diagnostic of tsunami deposits. Sandy storm deposits tend to be > 30 cm thick, generally extend < 300 m from the beach, and will not advance beyond the antecedent macrotopography they are able to fill. They typically are composed of numerous subhorizontal planar laminae organized into multiple laminasets that are normally or inversely graded, they do not contain internal mud laminae and rarely contain mud intraclasts. Application of these distinguishing characteristics depends on their preservation potential and any deposit modifications that accompany burial.

The distinctions between tsunami and storm deposits are related to differences in the hydrodynamics and sediment-sorting processes during transport. Tsunami deposition results from a few high-velocity, long-period waves that entrain sediment from the shoreface, beach, and landward erosion zone. Tsunamis can have flow depths greater than 10 m, transport sediment primarily in suspension, and distribute the load over a broad region where sediment falls out of suspension when flow decelerates. In contrast, storm inundation generally is gradual and prolonged, consisting of many waves that erode beaches and dunes with no significant overland return flow until after the main flooding. Storm flow depths are commonly < 3 m, sediment is transported primarily as bed load by traction, and the load is deposited within a zone relatively close to the beach.  相似文献   


19.
《Sedimentary Geology》2006,183(1-2):145-156
Prehistoric depositional signatures for large-scale washover involving marine inundation events such as storms and tsunami have been the subject of considerable research over the last 15 years. Much of this research has focused on the identification of sandsheets in back-barrier environments as depositional records for extreme washover events. All these deposits must have a sediment source and, by their nature, the most likely source of sediment for washover into back-barrier environments is the barrier itself. This study identifies an erosional signature for large-scale washover from a small coastal barrier on the southeast Australian coast. A distinct lens of marine sand, up to 90 cm thick, confined vertically by peat, is found in the upper fill of a closed freshwater back-barrier lagoon sequence. This sand lens is attributed to a large-scale washover event during the last 800 years, and was possibly deposited by a tsunami. The hypothesis for this study was that any event that breached the dune system must have caused considerable geomorphic change to the dunes and hence may have left an erosional signature. Ground penetrating radar transects of the system show an erosional contact between a series of truncated pre-event dunes and several small overlying post-event dunes. This study outlines a relatively simple non-invasive method for the identification of an erosional signature for prehistoric large-scale washovers caused by storm surge, exceptionally large waves, or tsunami.  相似文献   

20.
Tsunami deposits preserved in the geological record provide a more comprehensive understanding of their patterns of frequency and intensity over longer timescales; but recognizing tsunami deposits can prove challenging due to post-depositional changes, lack of contrast between the deposits and surrounding sedimentary layers, and differentiating between tsunami and storm deposition. Modern baseline studies address these challenges by providing insight into modern spatial distributions that can be compared with palaeotsunami deposits. This study documents the spatial fingerprint of grain size and foraminifera from Hasunuma Beach and the Kujukuri shelf to provide a basis from which tsunami deposits can be interpreted. At Hasunuma Beach, approximately 50 km east of Tokyo, the spatial distribution of three common proxies (foraminiferal taxonomy, foraminiferal taphonomy and sediment grain size) for tsunami identification were mapped and clustered using Partitioning Around Medoids cluster analysis. Partitioning Around Medoids cluster analysis objectively discriminated two coastal zones corresponding to onshore and offshore sample locations. Results show that onshore samples are characterized by coarser grain sizes (medium to coarse sand) and higher abundances of Pararotalia nipponica (27 to 63%) than offshore samples, which are characterized by finer grain sizes (fine to medium sand), lower abundances of Pararotalia nipponica (2 to 19%) and Ammonia parkinsoniana (0 to 10%), higher abundances of planktonics (15 to 58%) and species with fragile tests including Uvigerinella glabra. When compared to grain-size and foraminiferal taxonomy, foraminiferal taphonomy; i.e. surface condition of foraminifera, a proxy not commonly used to identify tsunami deposits, was most effective in discriminating modern coastal zones (identified supratidal, intertidal and offshore environments) and determining sediment provenance for tsunami deposits at Kujukuri. This modern baseline study assists the interpretation of tsunami deposits in the geological record because it provides a basis for sediment provenance to be determined.  相似文献   

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