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51.
Structural and engineering geology of the East Gate Landslide, Purcell Mountains, British Columbia, Canada 总被引:3,自引:0,他引:3
The East Gate Landslide is a prehistoric landslide that was reactivated in January 1997. The slope failure took place in the lower greenschist metasedimentary units of the Precambrian Horsethief Creek Group. The Grizzly Creek Thrust is a regional overturned fault that coincides with the location of the headscarp of the East Gate Landslide. Four discontinuity sets were recognised from detailed engineering geological mapping of the headscarp and surrounding area. The main scarp of the section reactivated in 1997 was sub-divided into three structural domains based on its position within the landslide, lithology, and orientation of the discontinuity sets. Limit-equilibrium techniques, finite-difference (FLAC) and distinct-element (UDEC) codes were used to investigate the failure mechanism of the 1997 event. The results of the field observations and numerical models suggest that the 1997 failure involved a complex mechanism incorporating components of rock-slumping, bi-planar, and pseudo-circular failure that was controlled by both the orientation of the discontinuity sets and reduced rock-mass quality due to tectonic deformation. 相似文献
52.
Metamorphic P-T paths have been derived for staurolite-kyanitegrade and garnet grade rocks from the Orfordville Belt, west-centralNew Hampshire. P-T paths calculated from garnet zoning are consistentwith parageneses observed in amphibolites as determined froma petrogenetic grid derived for amphibolites. The P-T pathsfrom the staurolite-kyanite zone show a pressure maximum at6.5 to 7.5 kb and {small tilde} 500?C followed by heating anddecompression to approximately 5 kb, 580?C, and a final phaseof near isobaric cooling. The path from the garnet zone is similar,but does not show the final phase of isobaric cooling. Both nappe-stage and dome-stage folds are observed in the OrfordvilleBelt. Comparison of mesoscale structures with mineral growthindicates that the nappe stage deformation occurred near orbefore the pressure maximum and dome stage deformation tookplace along the decompression-heating path. The last phase ofnear isobaric cooling may have resulted from rapid verticalreadjustment of the Orfordville Belt. 相似文献
53.
In July 2005, a debris flow and a water flood occurred on two adjacent gullies in the White River area, on northern Vancouver
Island in British Columbia, Canada. The 16,000 m3 debris flow buried approximately 7.5 ha of second-growth trees, buried approximately 500 m of a forestry road, and reached
two fish-bearing streams. The water flood eroded approximately 240 m of the same forestry road and plugged four culverts before
overtopping and inundating the road. To better plan for future events, risk analyses of debris flows, debris floods, and water
floods were carried out for the two gullies involved, plus a third adjacent gully. The elements at risk that were analyzed
included, in order of priority: users of the forestry road, the fish-bearing streams, the forestry road itself, and a timber
bridge. Using a series of qualitative, but defined, relative-risk matrices, the following components of specific risk were
estimated for each of the three types of events on each of the three gullies for each of the four elements at risk: probability
of occurrence, probability that the event will reach or otherwise affect the site of the element at risk, the probability
that the element at risk will be at the site when the event occurs, and the probability of loss or damage resulting from the
element being at the site when the event occurs. 相似文献
54.
Peter Hoppe Doug MacDougall Günter W. Lugmair 《Meteoritics & planetary science》2007,42(7-8):1309-1320
Abstract— Aqueous activity on meteorite parent bodies is indicated by the presence of carbonates. High spatial resolution ion microprobe analyses of nine individual carbonate grains (four dolomites, five breunnerites) from the Orgueil meteorite reveal linear correlations between 53Cr excesses and Mn/Cr ratios in all grains, indicative of in situ decay of radioactive 53Mn (half‐life 3.7 million years). The well‐defined isochrons appear to have chronological significance. If this is the case, then 53Mn/55Mn ratios between 2.1 and 4.7 × 10?6 are inferred for the time of carbonate formation and absolute ages of between 4561 and 4565 Ma are calculated (systematic uncertainty of ±2 Ma). Dolomites tend to have formed slightly earlier than the breunnerites. Our data imply extensive aqueous activity on the Orgueil parent body over a period of several million years, starting ~3–4 Myr after formation of the solar system, that most likely was the result of impact heating and latent heat from the decay of radioactive 26Al and 60Fe. 相似文献
55.
Andrés E. Piatti João F. C. SantosJr Juan J. Clariá Eduardo Bica Ata Sarajedini Doug Geisler 《Monthly notices of the Royal Astronomical Society》2001,325(2):792-802
Colour–magnitude diagrams are presented for the first time for L32, L38, K28 (L43), K44 (L68) and L116, which are clusters projected on to the outer parts of the Small Magellanic Cloud (SMC). The photometry was carried out in the Washington system C and T 1 filters, allowing the determination of ages by means of the magnitude difference between the red giant clump and the main-sequence turn-off, and metallicities from the red giant branch locus. The clusters have ages in the range 2–6 Gyr , and metallicities in the range −1.65<[Fe/H]<−1.10, increasing the sample of intermediate-age clusters in the SMC. L116, the outermost cluster projected on to the SMC, is a foreground cluster, and somewhat closer to us than the Large Magellanic Cloud. Our results, combined with those for other clusters in the literature, show epochs of sudden chemical enrichment in the age–metallicity plane, which favour a bursting star formation history as opposed to a continuous one for the SMC. 相似文献
56.
Seamless integration of spatial statistics and GIS: The S-PLUS for ArcView and the S+Grassland Links
Shuming Bao Luc Anselin Doug Martin Diana Stralberg 《Journal of Geographical Systems》2000,2(3):287-306
The extension of the functional capacity of geographic information systems (GIS) with tools for statistical analysis in general
and exploratory spatial data analysis (ESDA) in particular has been an increasingly active area of research in recent years.
In this paper, two operational implementations that combine the functionality of spatial data analysis software with a GIS
are considered more closely. They consist of linkages between the S-PLUS software for data analysis and two different GIS implementations, the ArcView desktop system, which is mostly vector-oriented, and the primarily raster-based Grassland open GIS environment. We emphasize conceptual and technical issues related to the software implementation of these approaches
and suggest future directions for linking spatial statistics and GIS.
Received: 14 January 1999 / Accepted: 11 May 1999 相似文献
57.
58.
59.
Lewis A. Owen Lyn Gualtieri Robert C. Finkel Marc W. Caffee Doug I. Benn Milap C. Sharma 《第四纪科学杂志》2001,16(6):555-563
The timing of glaciation in the Lahul Himalaya of northern India was ascertained using the concentrations of cosmogenic 10Be and 26Al from boulders on moraines and drumlins, and from glacially polished bedrock surfaces. Five glacial stages were identified: Sonapani I and II, Kulti, Batal and Chandra. Of these, cosmogenic exposure ages were obtained on samples representative of the Batal and Kulti glacial cycles. Stratigraphical relationships indicate that the Sonapani I and II are younger. No age was obtained for the Chandra glacial advance. Batal Glacial Stage deposits are found throughout the valley, indicating the presence of an extensive valley glacial system. During the Kulti Stage, glaciers advanced ca. 10 km beyond their current positions. Moraines produced during the Batal Stage, ca. 12–15.5 ka, are coeval with the Northern Hemisphere Late‐glacial Interstadial (Bølling/Allerød). Deglaciation of the Batal Glacial Stage was completed by ca. 12 ka and was followed by the Kulti Glacial Stage during the early Holocene, at ca. 10–11.4 ka. On millennial time‐scales, glacier oscillations in the Lahul Himalaya apparently reflect periods of positive mass‐balance coincident with times of increased insolation. During these periods the South Asian summer monsoon strengthened and/or extended its influence further north and west, thereby enhancing high‐altitude summer snowfall. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
60.
Andrés E. Piatti Ata Sarajedini Doug Geisler Eduardo Bica Juan J. Clariá 《Monthly notices of the Royal Astronomical Society》2002,329(3):556-566
We carried out Washington system photometry of the intermediate-age Large Magellanic Cloud (LMC) star clusters NGC 2155 and SL 896 (LW 480). We derive ages and metallicities from the T 1 versus colour–magnitude diagrams (CMDs). For the first time an age has been obtained for SL 896, . For NGC 2155 we derive . The two clusters basically define the lower age limit of the LMC age gap. In particular, NGC 2155 is confirmed as the oldest intermediate-age LMC cluster so far studied. The derived metallicities are and for NGC 2155 and SL 896, respectively. We also studied the CMDs of the surrounding fields, which have a dominant turn-off comparable to that of the clusters themselves, and similar metallicity, showing that one is dealing with an intermediate-age disc where clusters and field stars have the same origin. We inserted the present clusters in the LMC and Small Magellanic Cloud (SMC) age–metallicity relations, using a set of homogeneous determinations with the same method as in our previous studies, now totalling 15 LMC clusters and four SMC clusters, together with some additional values from the literature. The LMC and SMC age–metallicity relations appear to be remarkably complementary, since the SMC was actively star-forming during the LMC quiescent age gap epoch. 相似文献