This paper employs a numerical model of tsunami propagation together with documented observations and field measurements of
the evidence left behind by the tsunami in December 2004, to identify and interpret the factors that have contributed to the
significant spatial variability of the level of tsunami impact along the coastal belt of the eastern province of Sri Lanka.
The model results considered in the present analysis include the distribution of the amplitude of the tsunami and the pattern
of wave propagation over the continental shelf off the east coast, while the field data examined comprise the maximum water
levels measured at or near the shoreline, the horizontal inundation distances and the number of housing and other buildings
damaged. The computed maximum amplitude of the tsunami at water points nearest the shoreline along the east coast shows considerable
variation ranging from 2.2 m to 11.4 m with a mean value of 5.7 m; moreover, the computed amplitudes agree well with the available
field measurements. We also show that the shelf bathymetry off the east coast, particularly the submarine canyons at several
locations, significantly influences the near-shore transformation of tsunami waves, and consequently, the spatial variation
of the maximum water levels along the coastline. The measured values of inundation also show significant variation along the
east coast and range from 70 m to 4560 m with a median value of 700 m. Our analyses of field data also show the dominant influence
of the coastal topography and geomorphology on the extent of tsunami inundation. Furthermore, the measured inundation distances
indicate no apparent correlation with the computed tsunami heights at the respective locations. We also show that both the
computed tsunami heights and the measured inundation distances for the east coast closely follow the log-normal statistical
distribution. 相似文献
J.L. Hough in 1962 recognized an erosional unconformity in the upper section of early postglacial lake sediments in northwestern
Lake Huron. Low-level Lake Stanley was defined at 70 m below present water surface on the basis of this observation, and was
inferred to follow the Main Algonquin highstand and Post-Algonquin lake phases about 10 14C ka, a seminal contribution to the understanding of Great Lakes history. Lake Stanley was thought to have overflowed from
the Huron basin through the Georgian Bay basin and the glacio-isostatically depressed North Bay outlet to Ottawa and St. Lawrence
rivers. For this overflow to have occurred, Hough assumed that post-Algonquin glacial rebound was delayed until after the
Lake Stanley phase.
A re-examination of sediment stratigraphy in northwestern Lake Huron using seismic reflection and new core data corroborates
the sedimentological evidence of Hough’s Stanley unconformity, but not its inferred chronology or the level of the associated
lowstand. Erosion of previously deposited sediment, causing the gap in the sediment sequence down to 70 m present depth, is
attributed to wave erosion in the shoreface of the Lake Stanley lowstand. Allowing for non-deposition of muddy sediment in
the upper 20 m approximately of water depth as occurs in the present Great Lakes, the inferred water level of the Stanley
lowstand is repositioned at 50 m below present in northwestern Lake Huron. The age of this lowstand is about 7.9 ± 0.314C ka, determined from the inferred 14C age of the unconformity by radiocarbon-dated geomagnetic secular variation in six new cores. This relatively young age shows
that the lowstand defined by Hough’s Stanley unconformity is the late Lake Stanley phase of the northern Huron basin, youngest
of three lowstands following the Algonquin lake phases. Reconstruction of uplift histories for lake level and outlets shows
that late Lake Stanley was about 25–30 m below the North Bay outlet, and about 10 m below the sill of the Huron basin. The
late Stanley lowstand was hydrologically closed, consistent with independent evidence for dry regional climate at this time.
A similar analysis of the Chippewa unconformity shows that the Lake Michigan basin also hosted a hydrologically closed lowstand,
late Lake Chippewa. This phase of closed lowstands is new to the geological history of the Great Lakes.
This is the ninth in a series of ten papers published in this special issue of Journal of Paleolimnology. These papers were presented at the 47th Annual Meeting of the International Association for Great Lakes Research (2004),
held at the University of Waterloo, Waterloo, Ontario, Canada. P.F. Karrow and C.F.M Lewis were guest editors of this special
issue. 相似文献
Six low abundance rock reference materials (basalt BIR-1, dunite DTS-1, dolerite DNC-1, peridotite PCC-1, serpentine UB-N and basalt TAFAHI) have been analysed for high field strength elements (Zr, Nb, Hf, Ta, Th and U), Rb, Sr, Mo, Sb, Cs, Tl and Bi at ng g−1 levels (in rock) by magnetic sector inductively coupled plasma-mass spectrometry after HF/HClO4 high pressure decomposition. The adopted method uses only indium as an internal standard. Detection limits were found to be in the range of 0.08 to 16.2 pg ml−1 in solution (equivalent to 0.08 to 16.2 ng g−1 in rock). Our data for high field strength elements, Rb, Sr, Mo, Sb, Cs, Tl and Bi for the six selected low abundance geological reference materials show general agreement with previously published data. Our Ta values in DTS-1 and PCC-1 (1.3 and 0.5 ng g−1) are lower than in previously published studies, providing smooth primitive mantle distribution patterns. Lower values were also found for Tl in BIR-1, DTS-1 and PCC-1 (2, 0.4 and 0.8 ng g−1). Compared with quadrupole ICP-MS studies, the proposed magnetic sector ICP-MS method can generally provide better detection limits, so that the measurement of high field strength elements, Rb, Sr, Mo, Sb, Cs, Tl and Bi at ng g−1 levels can be achieved without pre-concentration, ion exchange separation or other specialised techniques. 相似文献
Tropical Africa is often seen to have problem economies that are very much alike and suffer from the same development problems. This view is questioned in exploratory analyses of levels of wealth, spatial productivity, the structure of the economy and aspects of the openness of economies and the way they have changed between 1965 and 1995. The analyses reveal differences between economies in both degree and kind. Change to economies was not unidirectional so that they became more disparate and differentiated. The exploratory analyses were extended using factor analysis as a diagnostic tool on a 19-variable by 25 country data set for 1985, 1990 and 1995. This confirmed the findings of the exploratory analyses and revealed changes in the structure of the factors reflecting development in the period. The results are discussed in the context of the literature in a search for explanation and policy formulation. 相似文献
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