Groundwater behaviour in Madeira, volcanic island (Portugal)     

Susana Nascimento Prada  Manuel Oliveira da Silva  José Virgílio Cruz 《Hydrogeology Journal》2005,13(5-6):800-812

Madeira Island is a hot-spot originating from a mantle plume. K-Ar age determinations indicate that the emerged part of the island was generated during Post-Miocene times 6000–7000 years B.P. Groundwater occurs in perched-water bodies, spring discharge from them is high, about 3,650 l/s; in dike-impounded water and basal groundwater. Basal groundwater is exploited by tunnels (1,100 l/s) and wells (1,100 l/s). Hydraulic gradients range from 10^–4 to 10^–2 and transmissivity ranges from 1.16×10^–2 to 2.89×10^–1 m²/s, indicating the heterogeneity of the volcanic aquifers. Water mineralisation is variable, and electrical conductivity ranges from 50 to 3,300 S/cm. There is a difference between groundwater discharging from perched-water bodies (43–201 S/cm) and from basal groundwater (109–3,300 S/cm). Groundwater average pH is 7.37, with waters acid to slightly alkaline (6.13–8.4), and generally cold. Nevertheless, a few samples associated with fault zones can be classified as thermal waters.

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Resumen La Isla de Madeira tuvo origen en un punto caliente proveniente de una pluma del manto. Las dataciones K – Ar, indican que la parte emergida de la isla se formó durante en Post—Mioceno, hace unos 6000–7000 años. El agua subterránea se encuentra en acuíferos colgados, cuya descarga a través de manantiales es alta, alrededor de 3650 l/s; también como agua retenida en diques o bien como agua subterránea propiamente dicha. Esta última es explotada por túneles (1100 l/s) y pozos (1100 l/s). Los gradientes hidráulicos varían desde 10–4 hasta 10–2 y la transmisividad varía desde 1.16×10^–2 hasta 2.89×10^–1 m²/s, indicando la heterogeneidad de los acuíferos volcánicos. La mineralización de agua es variable y la conductividad eléctrica varía desde 50 mS/cm hasta 3300 mS/cm. Hay una diferencia entre el agua subterránea proveniente de acuíferos colgados (43–201 mS/cm) y aquella del acuífero principal (109–3300 mS/cm). El pH promedio para el agua subterránea es 7.37; con variación desde ácida hasta ligeramente alcalina (6.13–8.4), y es generalmente fría. Sin embargo unos pocos ejemplos asociados con zonas de falla, pueden ser clasificados como agua termal.

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Résumé Lîle de Madeira est un point chaud, provenant dun panache mantélique. Les datations par la méthode de K-Ar indiquent que la part émergée de lîle a été générée pendant le Post Miocène, il y a 6000–7000 ans. Les eaux souterraines sont cantonnées dans des aquifères perchées qui se déchargent par des sources à grands débits, avec des valeurs dapproximativement de 3500 l/s, ainsi que dans les dikes. Une importante quantité des eaux souterraine se trouve sur la forme deau de fonds, formant une nappe basale, qui est exploitée par des tunnels (1100 l/s) et par des puits (1100 l/s). Les gradients hydrauliques ont des valeurs dans lintervalle de 10^–2 à 10^–4, tandis que les transmissivités se rangent entre 1.16×10^–2 m²/s et 2.81×10^–1 m²/s, ce quindique la hétérogénéité de laquifère volcanique. La minéralisation des eaux est aussi variable avec des conductivités électriques qui se rangent ente 50 mS/cm et 3300 mS/cm. Il y a une différence entre la conductivité des eaux provenant des aquifères perchées (30–201 mS/cm) par rapport à la conductivité les eaux de la nappe basale (109–3300 mS/cm). Le pH moyen est de 7.37 avec des valeurs de 6.13 pour les eaux acides et de 8.4 pour les eaux à faible alcalinité. En général il sagit des eaux froides, mais quelques échantillons provenant des zones faillées peuvent être classifiés comme des eaux thermales.

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The End-to-End Attribution Problem: From Emissions to Impacts     

Dáithí?A.?StoneEmail author  Myles?R.?Allen 《Climatic change》2005,71(3):303-318

When a damaging extreme meteorological event occurs, the question often arises as to whether that event was caused by anthropogenic greenhouse gas emissions. The question is more than academic, since people affected by the event will be interested in recurring damages if they find that someone is at fault. However, since this extreme event could have occurred by chance in an unperturbed climate, we are currently unable to properly respond to this question. A solution lies in recognising the similarity with the cause-effect issue in the epidemiological field. The approach there is to consider the changes in the risk of the event occurring as attributable, as against the occurrence of the event itself. Inherent in this approach is a recognition that knowledge of the change in risk as well as the amplitude of the forcing itself are uncertain. Consequently, the fraction of the risk attributable to the external forcing is a probabilistic quantity. Here we develop and demonstrate this methodology in the context of the climate change problem.  相似文献   

The seismic activity in Syria and Palestine during the middle of the 8th century; an amalgamation of historical earthquakes     

N.?N.?AmbraseysEmail author 《Journal of Seismology》2005,9(1):115-125

Some historical earthquakes are distinct owing to the geographical distance of the places affected. It is less clear, however, when more than one earthquake is amalgamated into a single event and their combined effects are attributed to a major event. In order to avoid gross overestimation of the size of historical earthquakes the separation and identification of the constituent earthquakes is an important consideration. As an example we show how the tendency of early and modern writers to amalgamate or duplicate earthquakes in Syria and Palestine can lead to the creation of major earthquakes, with serious consequences for the assessment of the seismic hazard in the region.  相似文献   

Second Tesseral Harmonic Torque Due to the DynamicS of the Oceanic Surface Layer as Detected by TOPEX/POSEIDON Altimetry 1993-2000     

M. Burša  S. Kenyon  J. Kouba  Z. Šíma  V. Vatrt  V. Vítek  M. Vojtíšková 《Studia Geophysica et Geodaetica》2005,49(1):13-22

Estimates of the second tesseral torque due to the variations in the radial space position of the mean ocean surface as monitored by TOPEX/POSEIDON altimeter system are derived. The magnitude of the studied torque may be compared to the tidal torque and to the tesseral torque caused by deformations due to the Earths rotation. However, such torque estimates strongly depend on the thickness of the ocean surface layer adopted in the spherical model of which the dynamics is believed to be responsible for the derived torque. The dependence on the thickness is discussed.  相似文献   

Equations for the Estimation of Strong Ground Motions from Shallow Crustal Earthquakes Using Data from Europe and the Middle East: Horizontal Peak Ground Acceleration and Spectral Acceleration   总被引：25，自引：13，他引：12  

N.?N.?AmbraseysEmail author  J.?Douglas  S.?K.?Sarma  P.?M.?Smit 《Bulletin of Earthquake Engineering》2005,3(1):1-53

This article presents equations for the estimation of horizontal strong ground motions caused by shallow crustal earthquakes with magnitudes M_w 5 and distance to the surface projection of the fault less than 100km. These equations were derived by weighted regression analysis, used to remove observed magnitude-dependent variance, on a set of 595 strong-motion records recorded in Europe and the Middle East. Coefficients are included to model the effect of local site effects and faulting mechanism on the observed ground motions. The equations include coefficients to model the observed magnitude-dependent decay rate. The main findings of this study are that: short-period ground motions from small and moderate magnitude earthquakes decay faster than the commonly assumed 1/r, the average effect of differing faulting mechanisms is not large and corresponds to factors between 0.8 (normal and odd) and 1.3 (thrust) with respect to strike-slip motions and that the average long-period amplification caused by soft soil deposits is about 2.6 over those on rock sites. Disappointingly the standard deviations associated with the derived equations are not significantly lower than those found in previous studies.  相似文献   

Periodic Behavior and Stochastic Fluctuations of Solar Activity: Proper Orthogonal Decomposition Analysis     

Antonio?VecchioEmail author  Leonardo?Primavera  Vincenzo?Carbone  Luca?Sorriso-Valvo 《Solar physics》2005,229(2):359-372

We use the Proper Orthogonal Decomposition (POD) to investigate the spatiotemporal features of the solar activity. Daily observation in the period 1949–1996 of the green coronal emission line at 530.3 nm are used as indicators of the activity behavior. We show that few POD modes suffice in describing both the space and time main periodicities. In particular, being affected by a strongly energetic stochastic behavior, daily data are described by five POD modes, while two POD modes are enough to describe the butterfly diagram in monthly averaged data. Apart from the basic period T₀ = 11 years, using daily data we found evidences for intercycle temporal periodicities.  相似文献   

Exact cosmological solutions in Brans and Dicke's scalar-tensor theory,I     

H. Dehnen  O. Obregón 《Astrophysics and Space Science》1971,14(2):454-459

The exact solution is sought for the cosmological equations of Brans and Dicke's scalar-tensor theory when a power law exists between the gravitational constant and the radius of curvature of the universe. For the space of negative curvature no solution is possible. On the contrary for a closed space the gravitational constant and the radius of curvature increase linearly with respect to the age of the universe. The parameter of the scalar-tensor theory is necessarily negative and can be determined by the present values of the mass-density of the universe, the Hubble-constant and the gravitational constant. The solution has no analogy in Einstein's theory with vanishing cosmological constant, even when the deviations from Einstein's values of the solar relativistic effects are small.  相似文献   

Spin-forbidden resonance multiplets in light elements     

B. Edlén  H. P. Palenius  K. Bockasten  R. Hallin  J. Bromander 《Solar physics》1969,9(2):432-438

We present new laboratory data on the multiplets 2s ^{2 1} S -2s2p ³ P, 2s ²2p ² P - 2s2p ^{2 4} P, and 2s ²2p ^{2 3} P - 2s2p ^{3 5} S in nitrogen, oxygen and fluorine, and discuss theZ-dependence of their wave-numbers. These multiplets are very faint in laboratory light sources, but can become prominent in astrophysical sources of low density. Our results confirm the solar identifications of the nitrogen and oxygen multiplets made by Burtonet al. Predicted positions of the corresponding multiplets in neon are given.  相似文献   

Relationships between Holocene sea-level variations,trophic development,and climatic change in Negra Lagoon,Southern Uruguay     

R.?Bracco  H.?Inda  L.?del Puerto  C.?Casti?eira  P.?Sprechmann  F.?García-RodríguezEmail author 《Journal of Paleolimnology》2005,33(3):253-263

Paleolimnological data are presented on trophic development, climatic change and sea level variations in Negra Lagoon, a 142 km² coastal lagoon in southern Uruguay. Using a sediment core that extended to the early Holocene, analyses of organic matter, carbonate, diatoms and opal phytoliths allowed us to track changes in trophic state and paleosalinity levels, which were closely related to Holocene sea level variation, temperature and humidity. Diatom Association Zones (DAZ) corresponding to transgressive events were dominated by marine/brackish taxa and relatively low organic matter values, while those DAZ corresponding to regressive events showed increases in brackish/freshwater diatoms and organic matter. Opal Phytoliths Association Zones (OPAZ) also were identified, temperature and humidity indices were calculated, and climatic trends were inferred. During the middle Holocene (i.e., ~5000–4000 yr BP), cool–dry climatic conditions were established. After ~4000 yr BP, a transition from cool to warm–humid conditions was observed, but fully warm humid conditions established only after ~1700 yr BP. Such climatic amelioration led to increases in trophic state.  相似文献   

Origin and evolution of the earth-moon system     

Hannes Alfvén  Gustaf Arrhenius 《Earth, Moon, and Planets》1972,5(1-2):210-230

The origin and evolution of the Earth-Moon system is studied by comparing it to the satellite systems of other planets. The normal structure of a system of secondary bodies orbiting around a central body depends essentially on the mass of the central body. The Earth with a mass intermediate between Uranus and Mars should have a normal satellite system that consists of about half a dozen satellites each with a mass of a fraction of a percent of the lunar mass. Hence, the Moon is not likely to have been generated in the environment of the Earth by a normal accretion process as is claimed by some authors.Capture of satellites is quite a common process as shown by the fact that there are six satellites in the solar system which, because they are retrograde, must have been captured. There is little doubt that the Moon is also a captured satellite, but its capture orbit and tidal evolution are still incompletely understood.The Earth and the Moon are likely to have been formed from planetesimals accreting in particle swarms in Kepler orbits (jet streams). This process leads to the formation of a cool lunar interior with an outer layer accreted at increasingly higher temperatures. The primeval Earth should similarly have formed with a cool inner core surrounded in this case by a very strongly heated outer core and with a mantle accreted slowly and with a low average temperature but with intense transient heating at each individual impact site.  相似文献