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951.
Vít Vilímek Marco Luyo Zapata Jan Klimeš Zdeněk Patzelt Nelson Santillán 《Landslides》2005,2(2):107-115
In this article we describe natural hazards associated with outburst floods of Palcacocha Lake and landslide events on the slopes of its moraine dam, in Cojup Valley, Cordillera Blanca (Peru). These events occurred in the last 70 years and some of them resulted in disasters, which strongly affected the city of Huarás. Field investigations and reference expression hydrodynamic tests as well as archive satellite images and aerial pictures were used to describe the evolution of hazards connected with Palcacocha Lake. Expression hydrodynamic tests proved a high permeability of sandy gravels glacial sediments, which form the present-day lake dam. Seepage through the natural dam forming small ponds below the overflow spillways occurs. A retreat of the glacial tongue causing an increase of the lake volume and unloading of the slope toe areas are the most important recent processes that influence the potential hazards affecting the Cojup valley. The research has proved that the climate warming and ongoing deglaciation play a very significant role in the change of natural hazards conditions in high mountains. 相似文献
952.
Spatially distributed hydrologic models can be effectively utilized for flood event simulation over basins where a complex system of reservoirs affecting the natural flow regime is present. Flood peak attenuation through mountain reservoirs can, in fact, mitigate the impact of major floods in flood‐prone areas of the lower river valley. Assessment of this effect for a complex reservoir system is performed with a spatially distributed hydrologic model where the surface runoff formation and the hydraulic routing through each reservoir and the river system are performed at a fine spatial and time resolution. The Toce River basin is presented as a case study, because of the presence of 14 active hydroelectric dams that affect the natural flow regime. A recent extreme flood event is simulated using a multi‐realization kriging method for modelling the spatial distribution of rainfall. A sensitivity analysis of the key elements of the distributed hydrologic model is also performed. The flood hydrograph attenuation is assessed. Several possible reservoir storage conditions are used to characterize the initial condition of each reservoir. The results demonstrate how a distributed hydrologic model can contribute to defining strategies for reservoir management in flood mitigation. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
953.
A plastic scintillator counter with anticoincidence screen has been flown in two 4-hour balloon flights, at a floating altitude of 3.2 and 3.5 mb, during day-and night-time respectively. Comparison between the day-and night-time counting-rates gives an upper limit of 10–2n/cm2 sec above 45 MeV for the continuous emission flux.This upper limit is compared with those derived from other experiments in function of the neutron energy spectrum assumed, and also with the expected continuous emission deduced from solar proton fluxes reported in non-flare conditions. It is concluded that with present experimental techniques, non-flare solar neutron emission can be detected only if the proton fluxes observed represent less than 10–3 of the protons accelerated in the sun.This research has been sponsored in part by the Air Force Cambridge Research Laboratories through the European Office of Aerospace Research, OAR, USAF under contract F 61052-68-C-050.0 相似文献
954.
Fault plane solutions for earthquakes in the central Hellenic arc are analysed to determine the deformation and stress regimes
in the Hellenic subduction zone in the vicinity of Crete. Fault mechanisms for earthquakes recorded by various networks or
contained in global catalogues are collected. In addition, 34 fault plane solutions are determined for events recorded by
our own local temporary network on central Crete in 2000–2001. The entire data set of 264 source mechanisms is examined for
types of faulting and spatial clustering of mechanisms. Eight regions with significantly varying characteristic types of faulting
are identified of which the upper (Aegean) plate includes four. Three regions contain interplate seismicity along the Hellenic
arc from west to east and all events below are identified to occur within the subducting African lithosphere. We perform stress
tensor inversion to each of the subsets in order to determine the stress field. Results indicate a uniform N-NNE direction
of relative plate motion between the Ionian Sea and Rhodes resulting in orthogonal convergence in the western forearc and
oblique (40–50∘) subduction in the eastern forearc. There, the plate boundary migrates towards the SE resulting in left-lateral strike-slip
faulting that extends to onshore Eastern Crete. N110∘E trending normal faulting in the Aegean plate at this part is in accordance with this model. Along-arc extension is observed
on Western Crete. Fault plane solutions for earthquakes within the dipping African lithosphere indicate that slab pull is
the dominant force within the subduction process and responsible for the roll-back of the Hellenic subduction zone. 相似文献
955.
956.
Environmental History of Lago di Tovel,Trento, Italy,Revealed by Sediment Cores and 3.5 kHz Seismic Mapping 总被引:1,自引:0,他引:1
Thomas?KulbeEmail author Flavio?Anselmetti Marco?Cantonati Michael?Sturm 《Journal of Paleolimnology》2005,34(3):325-337
Proxy data from a total of 30 sediment cores and information from a seismic survey show that the sedimentological and limnological history of Lago di Tovel (1178 m a.s.l.) has been significantly influenced by slope dynamics of its mountainous catchment. The lake represents a dead-ice lake with pro-glacial deposits at the base of its sedimentary record. A prominent lake level rise in 1597/1598 that increased maximum water depth from ∼20 to 39 m caused slope instabilities, leading to the deposition of mass-flow sediments with a maximum thickness of 2.5 m in the northern part of the lake and less than 50 cm in the southern part, resulting in a total volume of more than 113,000 m3. Consequently, a rough lake bottom morphology was produced, which led to distinct differences in sedimentation rates of 0.07 cm yr−1 on sills and 0.18 cm yr−1 within depressions. The age of the top of the mass-flow deposits was used to validate the ages of the younger, laminated sediments, which were dated by 210Pb and 137Cs. Lithological investigations showed that the sediments below the mass-flow deposits are also laminated and that they were not bioturbated. The long-term meromixis of Lago di Tovel is therefore mainly due to a combination of its topographic setting and the 5-month period of ice cover. Both prevent effective mixing of the lake by strong winds during spring and autumn. Distinct spatial differences in sediment distribution within the lake show that it is risky to interpret proxy data from only one coring site, even if the lake is very small. This is especially true in mountainous areas, where rock falls, mass movements, and slope instabilities of a significant size may have considerable effects on lakes. 相似文献
957.
958.
959.
960.
A. Deschamps F. Courboulex S. Gaffet A. Lomax J. Virieux A. Amato A. Azzara B. Castello C. Chiarabba G.B. Cimini M. Cocco M. Di Bona L. Margheriti F. Mele G. Selvaggi L. Chiaraluce D. Piccinini M. Ripepe 《Journal of Seismology》2000,4(4):377-386
We present the spatio-temporal distribution of more than 2000 earthquakesthat occurred during the Umbria-Marche seismic crisis, between September 26and November 3, 1997. This distribution was obtained from recordings of atemporary network that was installed after the occurrence of the first two largest shocks (Mw =, 5.7, Mw = 6.0) of September 26. This network wascomposed of 27 digital 3-components stations densely distributed in theepicentral area. The aftershock distribution covers a region of about 40 km long and about2 km wide along the NW-SE central Apennines chain. The activity is shallow,mostly located at less than 9 km depth. We distinguished three main zonesof different seismic activity from NW to SE. The central zone, that containsthe hypocenter of four earthquakes of magnitude larger than 5, was the moreactive and the more complex one. Sections at depth identify 40–50°dipping structures that agree well with the moment tensor focalmechanisms results. The clustering and the migration of seismicity from NW to SE and the generalfeatures are imaged by aftershock distribution both horizontally and at depth. 相似文献