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731.
The October 2005 earthquake triggered several thousand landslides in the Lesser Himalaya of Kashmir in northern Pakistan and
India. Analyses of ASTER satellite imagery from 2001 were compared with a study undertaken in 2005; the results show the extent
and nature of pre- and co-/post-seismic landsliding. Within a designated study area of ~2,250 km2, the number of landslides increased from 369 in 2001 to 2,252 in October 2005. Assuming a balanced baseline landsliding frequency
over the 4 years, most of the new landslides were likely triggered by the 2005 earthquake and its aftershocks. These landslides
mainly happened in specific geologic formations, along faults, rivers and roads, and in shrubland/grassland and agricultural
land. Preliminary results from repeat photographs from 2005 and 2006 after the snowmelt season reveal that much of the ongoing
landsliding occurred along rivers and roads, and the extensive earthquake-induced fissuring. Although the susceptibility zoning
success rate for 2001 was low, many of the co-/post-seismic landsliding in 2005 occurred in areas that had been defined as
being potentially dangerous on the 2001 map. While most of the area in 2001 was (very) highly susceptible to future landsliding,
most of the area in 2005 was only moderate to low susceptible, that is, most of the landsliding in 2005 actually occurred
in the potentially dangerous areas on the 2001 map. This study supports the view that although susceptibility zoning maps
represent a powerful tool in natural hazard management, caution is needed when developing and using such maps. 相似文献
732.
733.
We report Sr, Nd and Pb isotopic compositions of mid-Proterozoic anorthosites and related rocks (1.45-1.65 Ga) and of younger olivine diabase dikes (1.4 Ga) from two complexes on either side of the Grenville Front in Labrador. Anorthositic or diabasic samples from the Mealy Mountains (Grenville Province) and Harp Lake (Nain-Churchill Provinces) complexes have very similar major, minor and trace element compositions, but distinctly different isotopic signatures. All Mealy Mountains samples have ISr = 0.7025−0.7033, εNd = +0.6 to +5.6 and Pb isotopic compositions consistent with derivation from a mantle source depleted with respect to Nd/Sm and Rb/Sr. Pb isotopic compositions for the Mealy Mountains samples are slightly more radiogenic than model mantle compositions. All Harp Lake samples have ISr = 0.7032−0.7066, εNd = −0.3 to −4.4 and variable, but generally unradiogenic 207Pb/204Pb and 206Pb/204Pb compared to model mantle, suggesting mixing between a mantle-derived component and a U-depleted crustal contaminant. Crustal contaminants are probably a variety of Archean high-grade quartzofeldspathic gneisses with low U/Pb ratios and include a component that must be isotopically similar to the early Archean (>3.6 Ga) Uivak gneisses of Labrador or the Amitsoq gneisses of west Greenland. This would imply that the ancient gneiss complex of coastal Labrador and Greenland is larger than indicated by present surface exposure and may extend in the subsurface as far west as the Labrador Trough. If Harp Lake and Mealy Mountains samples were subjected to the same degree of contamination, as suggested by their chemical similarities, then the Mealy contaminants must be much younger, probably early or middle Proterozoic in age. The Labrador segment of the Grenville Front, therefore, appears to coincide with the southern margin of the Archean North Atlantic craton and may represent a pre mid-Proterozoic suture. 相似文献
734.
An acceleration scheme is proposed in a coupled ocean-atmosphere model for the simulation of long term climate evolutions forced by climate forcing of longer than millennia time scales. In this coordinated acceleration scheme, both the surface forcing and the deep ocean are accelerated simultaneously by the same factor. The acceleration scheme is evaluated in a 3-dimensional ocean general circulation model and in a coupled ocean-atmosphere model of intermediate complexity. For millennial climate evolution, our acceleration scheme produces reasonably good simulations with an acceleration factor of about 5. For climate evolution of even longer time scales, the acceleration factor can be increased further. 相似文献
735.
Regional- and district-level drivers of timber harvesting in European Russia after the collapse of the Soviet Union 总被引:1,自引:0,他引:1
Kelly J. Wendland David J. Lewis Jennifer Alix-Garcia Mutlu Ozdogan Matthias Baumann Volker C. Radeloff 《Global Environmental Change》2011,21(4):1290-1300
After the collapse of the Soviet Union, the forestry sector in Russia underwent substantial changes: the state forestry sector was decentralized, the timber industry was privatized, and timber use rights were allocated through short- and long-term leases. To date, there has been no quantitative assessment of the drivers of timber harvesting in European Russia following these changes. In this paper we estimate an econometric model of timber harvesting using remote sensing estimations of forest disturbance from 1990–2000 to 2000–2005 as our dependent variable. We aggregate forest disturbance to administrative districts – equivalent to counties in the United States – and test the impact of several biophysical and economic factors on timber harvesting. Additionally, we examine the impact that regions – equivalent to states in the United States and the main level of decentralized governance in Russia – have on timber harvesting by estimating the influence of regional-level effects on forest disturbance in our econometric model. Russian regions diverged considerably in political and economic conditions after the collapse of the Soviet Union, and the question is if these variations impacted timber harvesting after controlling for district-level biophysical and economic drivers. We find that the most important drivers of timber harvesting at the district level are road density, the percent of evergreen forest, and the total area of forest. The influence of these variables on timber harvesting changed over time and there was more harvesting closer to urban areas in 2000–2005. Even though district-level variables explain more than 70 percent of the variation in forest disturbance in our econometric model, we find that regional-level effects remain statistically significant. While we cannot identify the exact mechanism through which regional-level effects impact timber harvesting, our results suggest that sub-national differences can have a large and statistically significant impact on land-use outcomes and should be considered in policy design and evaluation. 相似文献
736.
Lewis D. Ashwal Michael A. Hamilton Vincent P. I. Morel Roger A. Rambeloson 《Contributions to Mineralogy and Petrology》1998,133(4):389-401
Four massif-type anorthosite bodies 25–100 km2 in area occur within high-pressure granulite facies supracrustal gneisses in southwestern Madagascar. Two of these bodies
(Ankafotia and Saririaky) appear to have been pulled apart by 40 km in a ductile shear zone, but structural features such
as sub-vertical stretching lineations indicate an origin by intense west-directed flattening and pure shear. Country rocks
(Graphite Series) include abundant graphite schist (some with >60% graphite), marble, quartzite, and minor amphibolite and
leucogneiss. Comagmatic granitoids (e.g. charnockites) are conspicuously absent. The anorthosite bodies are dominated by coarse
grained anorthosites and leuconorites (feldspars typically 3–5 cm, up to 1 m); minor norites and oxide-rich ferrogabbros occur
near the margins, but ultramafic rocks are absent. Typical mineralogy of the anorthositic rocks is: plagioclase (An41–54) + orthopyroxene (En38–66) ± augite (Mg♯ = 32–68) ± ilmenite ± magnetite ± apatite. High-alumina (to 6.1 wt% Al2O3) orthopyroxene megacrysts are widespread; most have exsolutions of calcic plagioclase (An72–85) but some contain garnet lamellae. Metamorphism has produced abundant recrystallization and sporadic coronitic garnet (Mg
♯=12–36) + clinopyroxene assemblages. Rb-Sr isotopic analyses of whole-rocks and minerals reveal no meaningful age relationships.
The age of late Neoproterozoic metamorphism is best constrained at 559 ± 50 Ma by a 6-point Sm-Nd mineral isochron (whole
rock, plag, pyx, ilm, apat, gar) from a Saririaky oxide-rich gabbro. The igneous crystallization age of the anorthosites is
estimated at 660 ± 60 Ma by a 19-point combined whole-rock and mineral Sm-Nd isochron for samples from both the Ankafotia
and Saririaky bodies. Initial isotopic ratios calculated at 0.66 Ga among 13 whole rocks are: Nd=+2.6 to +5.2 (mean=+3.7) and ISr=0.70328–0.70407 (mean=0.70347), indicating derivation of the Malagasy anorthosites from a depleted mantle source, and little,
if any, contamination with Archean crustal material. One anorthosite sample with Nd=−1.4 and ISr=0.70344 (calculated at 0.66 Ga) probably reflects the effects of assimilation of Early to Middle Proterozoic crustal basement,
but typical surrounding graphite schist (Nd=+0.3, ISr=0.70636, both at 0.66 Ga; TDM= 1131 Ma) represents only a minor potential contaminant for the anorthosite bodies. TDM model ages of the Malagasy anorthosites (797–1280 Ma; mean of 14 samples=949 Ma), as those of most other massif-type anorthosites,
are older than the true crystallization age, because of crustal contamination effects. Our isotopic data, together with recent
U-Pb data from the anorthosites and surrounding country rocks, are consistent with emplacement of the Malagasy anorthosite
bodies at or before the start of a protracted, high-grade metamorphic event or series of events between about 630 and 550 Ma.
This period coincides with the collision between, and amalgamation of, East and West Gondwana.
Received: 19 December 1997 / Accepted: 12 June 1998 相似文献
737.
738.