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This paper addresses the problem of characterizing the shape of a geological surface on the basis of its principal curvatures.
The surface is assumed to be modeled as a set of adjacent triangles defined by the location of their vertices and a method
is proposed for estimating numerically the principal curvatures at the vertices of the triangles using a local C2 interpolant. Also shown is how principal curvatures can be useful for studying the deformation of a geological surface (with
application to 3D balanced unfolding), and analyzing the folding or faulting of the interface between two adjacent layers. 相似文献
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Compilation of the offshore and onshore altitudinal limits of the loess deposits of western France and southern England shows that they were deposited by low-level wind fields. These relate to (i) the deflation of silt-rich sediment extracted from the outwash plains of the not far distant British–Irish Ice Sheet and from the palaeo-rivers of the Channel, and (ii) the existence of north and north-western palaeo-winds deduced from particle size analysis and heavy mineral distribution, and suggest (iii) that loess particles were transported by strong katabatic winds blowing from the northern ice-covered regions towards Brittany and Normandy. Comparison between the main orientation of Neanderthal shelters and the direction of the katabatic winds shows that they were perpendicular to each other. The dominant orientation of the shelters was apparently ruled by these winds. A small-scale study concentrating on the penultimate glaciation shows that in contrast to Brittany and Normandy where loess deposits accumulated on north-facing cliffs, in England the same particles were deposited on the leeside of the hills. The existence of deflation zones, violently swept by Marine Isotope Stage 6 katabatic winds south of the British–Irish ice sheet, was probably at the origin of the restricted number of Neanderthals at that time in England. © 2021 John Wiley & Sons, Ltd. 相似文献
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S.T. Nelson B. Barton M.W. Burnett J.H. McBride L. Brown I. Spring 《地球表面变化过程与地形》2020,45(12):2940-2953
The Hawaiian Islands permit investigation of tropical chemical weathering rates and processes on a single rock type, basalt. Chronosequences are investigated as a function of rainfall due to the varying age of each island, including Kauai (~4 Ma), Oahu (~2 Ma), and Hawaii's Kohala Peninsula (~0.3 to 0.17 Ma). Understanding tropical critical zone (CZ) development is vital given the large populations in developing countries that rely on it. HVSR (horizontal-to-vertical spectral ratio) seismic soundings on Kauai indicate that ~60% of the variability in laterite thickness is due to gradients in precipitation, with errors in erosion corrections and variability in the original permeability structure of the volcanic sequence playing important roles. Basalts have higher horizontal than vertical hydraulic conductivity (Kh > Kv) , and local variability in likely drives much of the remaining differences in laterite thickness. HVSR is well suited for estimating laterite thickness as it has been shown to reliably detect the base of the weathering profile, is rapid (20 min/sounding), highly portable, and occupies a very small footprint. Comparison of Kauai and Oahu weathering profiles suggests that the Oahu laterites are fully or nearly fully formed, despite being half the age of Kauai. By contrast, the young laterites on Kohala (~170 to ~300 ka) exhibit greatly contrasting thicknesses, where coastal laterites are thick and interior laterites are thin, suggesting that early weathering on shield volcanoes produces wedge-shaped laterites near the coast. With time, the thick (coastal) end of the wedge propagates upslope such that a fully developed, constant-thickness laterite carapace can form in ~2 Ma or less. The development of thickened coastal laterites on young substrates depends on greater water–rock ratios as vertically infiltrating water upslope is diverted laterally. This view of laterite development is very different compared to endmember models of continental weathering and CZ development. © 2020 John Wiley & Sons, Ltd. 相似文献
6.
Building and Editing a Sealed Geological Model 总被引：1，自引：0，他引：1
Guillaume Caumon François Lepage Charles H. Sword Jean-Laurent Mallet 《Mathematical Geology》2004,36(4):405-424
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Jean-Laurent Mallet 《Mathematical Geology》2004,36(1):1-32
Interpolating physical properties in the subsurface is a recurrent problem in geology. In sedimentary geology, the geometry of the layers is generally known with a precision much superior to that which one can reasonably expect for the properties. The geometry of the layers is affected by folding and faulting since the time of deposition, whereas the distribution of properties is, to a certain extent, determined at the time of deposition. As a consequence, it may be wise to model first the geometry of the layers and then, simplify the geologic equation by removing the influence of that geometry. Inspired from the work of H. E. Wheeler on Time-Stratigraphy, we define, mathematically, a new space where all horizons are horizontal planes and where faults, if any, have disappeared. We surmise that this new space, however approximative, is better to model physical properties of the subsurface whatever the subsequent interpolation method used. The proposed mathematical framework also provides solutions to complex problems such as determination of strains resulting from tectonic events and up-scaling of permeabilities on structured and unstructured 3D grids. 相似文献
8.
Brian Mills Dan Unrau Carla Parkinson Brenda Jones Jennifer Yessis Kelsey Spring Laurel Pentelow 《Natural Hazards》2008,47(2):157-183
This article summarizes research completed to assess the risk of lightning-related injuries and fatalities in Canada. Although
lightning mortality has declined significantly over the past century, it remains a common meteorological hazard that regularly
kills and injures. Based on an analysis of media reports, vital statistics, hospital admission and emergency room visit records,
and fire loss data, the authors estimate that on average about 9–10 lightning-related deaths and 92–164 injuries occur each
year in Canada. The distribution of casualties reflects current provincial population and cloud-to-ground lightning densities.
Consistent with similar studies in other developed nations, most lightning-related fatalities and injuries in Canada occur
during the June-August summer season, coincident with peak lightning, and during the Thursday-Saturday period, most likely
related to higher rates of participation in outdoor activities. The majority of victims are male, less than 46 years old,
and engaged in outdoor recreational activities when injured or killed in a lightning incident. Media reports used in the study
were found to underestimate both lightning mortality (36%) and morbidity (20–600%).
相似文献
| Brian MillsEmail: |
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This article assesses the extent and costs of lightning-related damage and disruption in Canada. Lightning routinely damages
property and disrupts economic and social activities. Affected sectors include health; property and casualty insurance; forestry;
electricity generation, transmission, and distribution; agriculture; telecommunications; transportation; and tourism and recreation—the
first four sectors are the most important in terms of contributing to overall impacts and costs. Secondary data and extrapolations
from U.S. studies were used to develop cost estimates for the health, property, forestry, and electricity sectors. Aggregated,
annual lightning-related damage and disruption costs in Canada range from CA$600 million to CA$600 million to CA1 billion. Forestry and electricity
damages accounted for over 85% of the total. The estimates are both preliminary and conservative. In terms of continued research,
additional or more refined studies using Canadian empirical data are warranted for the insurance and electricity sectors.
Detailed insurance claim or outage data would permit analysis at the storm level and potentially discern finer-scaled risk
patterns. Further effort is also required to evaluate risk or damage prevention measures, particularly those that relate to
expanded or enriched use of the Canadian Lightning Detection Network data by both public and private sector clients. Both
the degree of adoption and efficacy or cost-effectiveness should be investigated. 相似文献
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