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671.
Defining a model of 3D seismogenic sources for Seismic Hazard Assessment applications: The case of central Apennines (Italy) 总被引:6,自引:0,他引:6
Geology-based methods for Probabilistic Seismic Hazard Assessment (PSHA) have been developing in Italy. These methods require information on the geometric, kinematic and energetic parameters of the major seismogenic faults. In this paper, we define a model of 3D seismogenic sources in the central Apennines of Italy. Our approach is mainly structural-seismotectonic: we integrate surface geology data (trace of active faults, i.e. 2D features) with seismicity and subsurface geological–geophysical data (3D approach). A fundamental step is to fix constraints on the thickness of the seismogenic layer and deep geometry of faults: we use constraints from the depth distribution of aftershock zones and background seismicity; we also use information on the structural style of the extensional deformation at crustal scale (mainly from seismic reflection data), as well as on the strength and behaviour (brittle versus plastic) of the crust by rheological profiling. Geological observations allow us to define a segmentation model consisting of major fault structures separated by first-order (kilometric scale) structural-geometric complexities considered as likely barriers to the propagation of major earthquake ruptures. Once defined the 3D fault features and the segmentation model, the step onward is the computation of the maximum magnitude of the expected earthquake (M
max). We compare three different estimates of M
max: (1) from association of past earthquakes to faults; (2) from 3D fault geometry and (3) from geometrical estimate corrected by earthquake scaling laws. By integrating all the data, we define a model of seismogenic sources (seismogenic boxes), which can be directly used for regional-scale PSHA. Preliminary applications of PSHA indicate that the 3D approach may allow to hazard scenarios more realistic than those previously proposed. 相似文献
672.
673.
The assessment of the loss potential caused by natural perils is a very important task for all insurance companies working in hazard-prone markets. It has to be based on two crucial items: the frequency of events and the investigation of their effects on the insured portfolio.This article deals with the second aspect, i.e. an evaluation of the insured damage caused by two earthquakes, namely those occurring near Albstadt, Germany, on 3 September 1978, and in central Chile on 3 March 1985. The results of the analysis of the earthquake in central Chile enable the mean damage ratio (damage in relation to the value) to be related to the height and the type of construction of the buildings affected. The Albstadt earthquake data permit an illustration of the effects of the type of subsoil on the mean damage ratio. The damage to individual buildings can be described by a lognormal distribution. Possible applications of these results are mentioned. 相似文献
674.
Interplanetary observations from Helios 1, Helios 2, and IMP-8 spacecraft during 1976 and 1977, namely the early portion of solar cycle 21, have been used to investigate the latitudinal gradients of the solar wind parameters with respect to the angular displacement from the current sheet inferred from synoptic HAO white-light maps of the solar corona at 1.75 solar radii. A latitudinal belt of ±25 deg around the current sheet has been investigated. Large gradients for solar wind flow speed, proton density and temperature have been found. Smoother gradients were also found for particle flux, kinetic, gravitational and thermal energy density flux. All these gradients revealed to become smoother going towards the solar cycle's maximum. Neither latitudinal nor temporal variations were identified for magnetic and thermal energy density. A remarkable result of this study is that the momentum flux density and the total energy flux density which other authors found to be independent of any longitudinal stream structure were also found to be independent of any latitudinal structure. Moreover, these two parameters did not show any temporal variation during the period of interest. 相似文献
675.
An extension of the seasonal climate model of R. D. Cess and J. Caldwell (1979, Icarus, 38, 349–357) to Saturn's upper troposphere is presented. The ring-modulated latitudinal dependence of the insolation, the ring thermal emission, the oblateness of the planet, the orbit eccentricity, and the latitudinal variation of the internal heat flux are taken into account. Calculations agree closely with the temperature—latitude profiles retrieved from Voyager IRIS measurements at atmospheric levels located above the 0.2-bar pressure level; they reproduce the observed large-scale hemispheric asymmetry which is then shown to result from the seasonally variable insolation. Aerosol absorption is found to be the dominant source of atmospheric solar heating in the troposphere and the model suggests an aerosol mean unit optical depth around the 0.25-bar level in the equatorial region and around the 0.35-bar level at other latitudes. The model fails to predict the retrieved temperature—latitude profiles below the 0.3-bar level. This discrepancy is attributed to the existence of clouds at these levels which are responsible for an additional far-infrared opacity not taken into account in the temperature retrieval. The cloud-top altitude would be about 0.3 bar except in the 20 to 40°N region where these clouds would be confined below the 0.6-bar level. The poor correlation between infrared measurements and visible images is discussed and a possible model of Saturn's cloud structure is proposed. 相似文献
676.
Effects of buoyancy and mechanical layering on collisional deformation of continental lithosphere: Results from physical modeling 总被引:1,自引:0,他引:1
We use two suites of lithospheric-scale physical experiments to investigate the manner in which deformation of the continental lithosphere is affected by both (1) variations of lithospheric density (quantified by the net buoyant mass per area in the lithospheric mantle layer, MB), and (2) the degree of coupling between the crust and lithospheric mantle (characterized by a modified Ampferer ratio, Am). The dynamics of the experiments can be characterized with a Rayleigh–Taylor type ratio, CLM. Models with a positively buoyant lithospheric mantle layer (MB > 0 and CLM > 0) result in distributed root formation and a wide deformation belt. In contrast, models with a negatively buoyant lithospheric mantle layer strongly coupled to the crust (MB < 0, 0 > CLM > ≈ − 0.2, and Am > ≈ 10− 3) exhibit localized roots and narrow deformation belts. Syncollisional delamination of the model lithospheric mantle layer and a wide deformation belt is exhibited in models with negatively buoyant lithospheric mantle layers weakly coupled to the crust (MB < 0, CLM < 0, and Am < ≈ 10− 3). Syncollisional delamination of the continental lithosphere may initiate due to buoyancy contrasts within the continental plate, instead of resulting from wedging by the opposing plate. Rayleigh–Taylor instabilities dominate the style of deformation in models with a negatively buoyant lithospheric mantle layer strongly coupled to the crust and a slow convergence rate (MB < 0 and CLM > ≈ − 0.2). The degree of coupling (Am) between the model crust and lithospheric mantle plays a lesser role in both the style of lower-lithospheric deformation and the width of the crustal deformed zone with increasing density of the lithospheric mantle layer. 相似文献
677.
Carmen Sanchez-Valle Bruno Reynard Christophe Lecuyer Jean-Claude Chervin 《Geochimica et cosmochimica acta》2005,69(17):4301-4313
Equilibrium boron isotopic fractionations between trigonal B(OH)3 and tetragonal B(OH)4− aqueous species have been calculated at high P-T conditions using measured vibrational spectra (Raman and IR) and force-field modeling to compute reduced partition function ratios for B-isotopic exchange following Urey’s theory. The calculated isotopic fractionation factor at 300 K, α3/4 = 1.0176(2), is slightly lower than the formerly calculated value of α3/4 = 1.0193 (Kakihana and Kotaka, 1977), due to differences in the determined vibrational frequencies. The effect of pressure on α3/4 up to 10 GPa and 723 K is shown to be negligible relative to temperature or speciation (pH) effects. Implications for the interpretation of boron fractionation in experimental and natural systems are discussed. We also show that the relationship between seawater-mineral B isotope fractionation and pH can be expressed using two variables, α3/4 on one hand, and the pKa of the boric acid-borate equilibrium on the other hand. This latter value is given by the equilibrium of boron species in water for the carbonate-water exchange, but could be governed by mineral surface properties in the case of clays. This may allow defining intrinsic paleo-pHmeters from B isotope fractionation between carbonate and authigenic minerals. Finally, it is shown that fractionation of boron isotopes can be rationalized in terms of the changes in 1) coordination of B from trigonal to tetrahedral in both fluids and minerals; and 2) the ligand nature around B from OH− in the fluid and some hydrous minerals to non-hydrogenated O in many minerals. Relationships are established that allow predicting the isotopic fractionation factor of B between minerals and fluid. 相似文献
678.
679.
Bruno Merz Jana Friedrich Markus Disse Jochen Schwarz Johann G. Goldammer Jochen Wächter 《Natural Hazards》2006,38(1-2):3-20
The German Research Network for Natural Disasters (DFNK) linked 15 partners with scientific expertise in the field of natural
hazards. Main objectives were the development and provision of the scientific fundamentals for an advanced risk management
of important natural disasters in Germany, i.e., floods, earthquakes, storms and wildland fires. This included risk analyses,
the development of information systems for supporting disaster management, and recommendations for risk reduction measures.
This paper gives an overview of DFNK and summarises its experiences concerning multidisciplinarity and user-orientation. It
illustrates the concept of risk chains, causally linking the different processes from hazard to risk. The step from hazard
to risk requires interdisciplinary research teams. The experiences show that integrative concepts allow results not achievable
with mono-disciplinary approaches. Integrative approaches pave the way to harmonised safety considerations taking into account
the different hazards in a region within a common framework. User-orientation, policy advice and development of operational
tools are key issues of disaster research. The experiences of DFNK illustrate the limitations of a research network in bridging
the gap between research and application within rather short-term projects. Successful cooperation with users could be established
by those activities where, at the beginning of the project, a user was identified who had a strong interest in solving an
urgent problem. 相似文献
680.
Experimental constraints on pre-eruption conditions of pantelleritic magmas: Evidence from the Eburru complex, Kenya Rift 总被引:1,自引:0,他引:1
The phase relationships and compositions of a pantellerite from the Eburru complex in the Kenya Rift Valley have been determined at 150 MPa and under reducing conditions, 2 log units below the Ni–NiO solid buffer. The effects of temperature and melt water content on phase relationships have been explored. Alkali feldspar and quartz crystallise alone at temperatures above 700 °C, irrespective of melt water content. Below 700 °C, sodic amphibole and clinopyroxene also crystallise; the amphibole being the liquidus phase under water-rich conditions. The coexistence of amphibole phenocrysts with alkali feldspar and quartz in a crystal-poor pantellerite implies temperatures below 700 °C and melt water contents higher than 4 wt.%, possibly up to 5–6 wt.%. Pantellerites have lower liquidus temperatures than associated comendites, which supports a parent–daughter relationship between the two magma types. The melts produced in the experiments extend the compositional trend displayed by the natural rock series, and reproduce some extreme compositions occasionally observed in alkaline volcanic series, with FeO contents above 12 wt.% and Na2O contents approaching 10 wt.%. Pantellerites are therefore the true near-minimum melt compositions of alkaline oversaturated magma series. 相似文献