Multi-day rainfall trends over the Iberian Peninsula     

Francisco Javier Acero  María Cruz Gallego  José Agustín García 《Theoretical and Applied Climatology》2012,108(3-4):411-423

In order to analyze the effects of the duration of precipitation events, trends in extreme rainfall over the Iberian Peninsula (IP) for multi-day extreme precipitation events (1 to 7?days) were evaluated from records of 52 observatories regularly distributed over Iberia with no missing data for the common period 1958–2004. Two approaches were used: first, the nonparametric Mann–Kendall test together with the Sen method, and second, a parametric test based on the statistical theory of extreme values, involving time-dependent parameters to account for possible temporal changes in the frequency distribution. It was found that, in winter, there were significant negative trends for a great part of the Iberian Peninsula, but significant positive trends for the southeast over areas that shrank as the number of days considered for the precipitation event increased. Spring also showed negative trends for a great part of the IP but with a major area of positive trend over the northeast that remained unchanged when considering the maxima of from 1 to 7?days of rainfall. Autumn showed a bipolar spatial pattern, with the west being positive and the east negative.  相似文献   

Geochemistry of soils along a transect from Central Mexico to the Pacific Coast: A pilot study for continental-scale geochemical mapping   总被引：2，自引：2，他引：0  

J.A. Chiprs  A. de la Calleja  J.I. Tellez  F. Jimnez  C. Cruz  E.G. Guerrero  J. Castro  M.G. Monroy  J.C. Salinas 《Applied Geochemistry》2009,24(8):1416

The Mexican Geological Survey (SGM), the National Institute of Statistics, Geography and Informatics (INEGI) and the Autonomous University of San Luis Potosi (UASLP) have established a multidisciplinary team with the objective of creating a national program of geochemical mapping of soils in Mexico. This is being done as part of the North American Soil Geochemical Landscapes Project in partnership with the US Geological Survey and the Geological Survey of Canada. As the first step, a pilot study was conducted over a transect that extends from the Mexico–US border near Ciudad Juarez in the north to the Pacific Ocean in the south. This pilot transect was conducted in two phases, and this paper presents results from the first phase, which sampled soils at about a 40-km spacing along a 730-km transect beginning in Central Mexico and ending at the Pacific Coast. Samples were collected from the A and C horizons at each site and 60 elements were analyzed. This pilot study demonstrates that geochemical mapping based on a 40-km spacing is adequate to identify broad-scale geochemical patterns. Geologic influence (i.e., soil parent material) was the most important factor influencing the distribution of elements along the transect, followed by the influence of regional mineralization. The study also showed that influence by human activities over the transect is minimal except possibly in large mining districts. A comparison of element abundance in the A horizon with the environmental soil guidelines in Mexico showed that the natural concentrations of the studied soils were lower than the established threshold for soil restoration with the exception of V and As. The former had a median value (75 mg/kg) approximately equal to the value established in Mexico for soil restoration in agricultural and residential lands (78 mg/kg), and the latter had three values higher than the 22 mg/kg threshold for soil restoration in agricultural and residential lands. These cases demonstrate the importance of knowing the national- and regional-scale geochemistry of Mexican soils as a support for the decision-making process, particularly for the proper formulation and application of soil guidelines designed to protect human and ecosystem health.  相似文献   

The Cretaceous–Tertiary transition in Guatemala: limestone breccia deposits from the South Petén basin     

W. Stinnesbeck  G. Keller  J. de la Cruz  C. de León  N. MacLeod  J. E. Whittaker 《International Journal of Earth Sciences》1997,86(3):686-709

Limestone breccia deposits in southern Mexico, Guatemala and Belize have recently been interpreted as proximal to distal ballistic fallout deposits, generated by a bolide impact that struck Yucatan at K/T boundary time. We review the age, lithology and the depositional environment of five K/T boundary sections in the South Petén area of Guatemala (Caribe, Aserradero, Chisec, Actela, Chemal) in order to evaluate the nature and origin of K/T limestone breccia deposition. The sections are located 500?km south of the proposed impact site at Chicxulub and trend in an east–west direction from the Guatemala/Mexico border to southern Belize. In four of the five sections examined, a breccia unit up to 50?m thick overlies reef-bearing shallow-water limestones of late Cretaceous (Campanian-Maastrichtian) age. Rhythmically bedded limestones, marls and siltstones of early Danian age overlie the breccia and were deposited under middle-to outer-neritic conditions. The breccia consists of differently coloured layers of shallow-water limestones. Clast size generally decreases upsection to thin layers of predominantly rounded clasts, and these fine-grained rudstones grade into grainstones at the top. In at least one section (EI Caribe) diagenetically altered glass spherules are present in the uppermost layers of the grainstone. These glass spherules are of stratigraphic position and chemical composition similar to black and yellow glass from Beloc, Haiti and Mimbral, Mexico, which some workers have chemically linked to melt glass within the breccia of the Chicxulub cores. We suggest that breccia deposition in Guatemala may have been multi-event, over an extended time period, and related to the collision of the Yucatan and Chortis plates as well as related to a major impact or volcanic event at the end of the Cretaceous.  相似文献   

Main features of the sea-breeze in Barcelona     

A. Redaño  J. Cruz  J. Lorente 《Meteorology and Atmospheric Physics》1991,46(3-4):175-179

Summary From a data set of sea-breeze observations corresponding to cases of no synoptic-scale flow in Barcelona during the period 1970–89, some features of this wind have been deduced. Maximum velocities of between 6–14 m/s generally occur during 12–16 SLT. Diurnal evolution gives a clockwise rotation of sea breeze so that this wind blows roughly parallel to the shoreline in late afternoon. The rate of the change of direction is in agreement with numerical results from a simple nonlinear sea breeze model.With 7 FiguresThis work has been supported by the DGICYT, Project No. PB87-0718.  相似文献   

Strong-motion accelerograph array in Santiago,Chile, and preliminary evaluation of site effects     

Saburoh Midorikawa  Rafael Riddell  Ernesto Cruz 《地震工程与结构动力学》1991,20(5):403-407

A strong-motion accelerograph array in Santiago, Chile has been installed. One of the sites is located on rock and the other six sites are on soil ground with different surface geology, so that local site effects on ground motions can be studied. As a preliminary evaluation of the site effects, the spectral ratios of weak-motion records at soil sites with respect to the rock site are calculated. The spectral ratios show that the amplification of ground motions with respect to the rock site is approximately 1.25 on dense gravel deposits, 2.5 on stiff pumice ground and 3.5 on soft silt ground.  相似文献   

Modified borehole jack method for elastic property determination in rocks     

R. V. de la Cruz 《Rock Mechanics and Rock Engineering》1978,10(4):221-239

SummaryModified Borehole Jack Method for Elastic Property Determination in Rocks This paper describes a method of determining thein-situ elastic properties of rock masses with friction-strain gauges and a lengthened borehole jack.The method involves impressing tangentially-oriented friction gauges on opposite quadrants of a borehole wall, while the remaining quadrants are loaded by the borehole jack with a unidirectional self-equilibrating pair of forces. The tangential normal strains generated at the borehole wall are thus measured concurrently with the loading. To determine the modulus of the rock mass, equations were developed relating the measured tangential normal strains and the applied ram pressures.Several factors which may influence the interpretation of data were thoroughly analyzed. It was shown that variations in the pressure distribution and area of plate-wall contact have negligible effects on the accuracy of data interpretation. End effects were minimized by lengthening the jack and carrying out strain measurements at the central region only where stresses and strains are homogeneous and plane strain conditions exist.The new method has the same desirable mechanical and operational features as the well-known Goodman-Jack method. Most important, however, its theoretical basis is exact with no estimated coefficients required in the reduction of observed data. While the method requires an ideal elastic material, it has a number of other applications for in-situ measurements besides modulus determination. The modified method could be utilized for determining linearity, anisotropy, inhomogeneity, tensile strength and, with an additional operation, the in-situ stress field.

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ZusammenfassungModifizierte Methode zur Bestimmung der elastischen Kenngröen von Fels mittels einer Bohrlochaufweitungssonde Es wird eine Methode zur Bestimmung der elastischen Kenngrößen von Fels aus In-situ-Versuchen mittels Reibungs-Dehn-meßstreifen und einer verlängerten Bohrlochaufweitungssonde beschrieben.Tangential orientierte Reibungsmeßstreifen werden an gegenüberliegenden Quadranten des Bohrloches angebracht, während die beiden anderen Quadranten mit der Bohrlochaufweitungssonde belastet werden, um Belastung und Verformung gleichzeitig zu messen. Gleichungen wurden entwickelt um daraus den Modul der Steinmasse zu bestimmen.Es wird gezeigt, daß eine ungleichmäßige Verteilung des Druckes und die Platten-Wand-Kontaktfläche einen unbedeuteten Einfluß auf die Exaktheit der Ergebnisse haben. Randeinflüsse wurden verringert, indem Messungen nur in der Mitte der Sonde ausgeführt wurden.Diese neue Methode hat dieselben Vorteile wie die bekannte Goodman-Jack Methode. Am wichtigsten ist aber, daß ihre theoretische Basis exakt ist. Obwohl die Methode nur in einem ideal elastischen Material anwendbar ist, kann sie außer für Modul-Bestimmung auch für andere In-situ-Messungen gebraucht werden, wie z. B. Linearität, Anisotropie, Inhomogenität, Zugfestigkeit und den primären Spannungszustand.

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RésuméMéthode modifiée pour déterminer les repères élastiques de rochers par une sonde d'élargissement de trous de sonde Cet article décrit une méthode de mesure des propriétés élastiquesin-situ des masses rocheuses, à l'aide d'indicateurs de déformation à friction, et d'un vérin alongé pour trou de sondage.La méthode consiste à imprimer des indicateurs de déformation à friction sur les quadrants opposés de la paroie d'un trou de sondage, et à charger les deux autre quadrants avec deux forces de même direction qui s'équilibrent, utilisant le vérin pour trou de sondage. Les déformations tangentielles normales créées sur la paroie du trou de sondage sont ainsi mesurées avec la charge correspondante. Afin de pouvoir déterminer le module d'élasticité de la masse rocheuse on a développé les équations qui relient les déformations normales tangentielles mesurées aux pressions appliquées.On a analysé en detail plusieurs facteurs qui pourraient influencer l'interprétation des données. On a montré que des variations dans la distribution de la pression, et dans la surface de contact entre le piston et la paroie, ont un effet négligeable sur la précision de l'interprétation des données. Les effets d'extrémités ont été réduits au minimum en alongeant le piston, et en ne mesurant les déformations que dans la région centrale, où les contraintes et déformations sont homogènes et des conditions de deformation plane existent.La nouvelle méthode a les mêmes caractéristiques mécaniques et opérationnelles désirables que la méthode bien connue Goodman-Jack. Encore plus important est le fait que sa base théorique est exacte, et il n'est pas nécessaire d'utiliser des coefficients estimés pour réduire les résultats observés. Bien que la méthode exige un milieu élastique idéal, elle peut être utilisée pour des mesuresin-situ autres que les mesures du module d'élasticité. La méthode modifiée pourrait être utilisée pour déterminer la linéarité, l'anisotropie, le manque d'homogénéité, la résistance à la traction et, avec une opération supplémentaire, le champ des forcesin-situ.

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With 6 Figures  相似文献   

A spectral analysis of Iberian Peninsula monthly rainfall   总被引：2，自引：0，他引：2  

J. A. García  A. Serrano  M. de la Cruz Gallego 《Theoretical and Applied Climatology》2002,71(1-2):77-95

Summary A spectral analysis of Iberian Peninsula monthly rainfall series was carried out. The data set consists of monthly precipitation records from 40 meteorological observatories over 74 years (1919–1992). The stations are representative of most of the Iberian Peninsula. The rainfall series were analyzed spatially by means of Principal Component Analysis (PCA) and temporally by means of the Multi-Taper Method (MTM) of spectral analysis of by Monte-Carlo Singular Spectrum Analysis (MCSSA). The PCA gave six dominant modes of variation which explain 75% of the variance with each component affecting a different region of the Peninsula. The spectral analysis showed 7 year oscillations for the dominant pattern and 2.7 and 16 years for the third pattern. The 7-year oscillation seems to be related to other climatic oscillations recorded in the northern hemisphere while the 2.7-year oscillation could be related to the ENSO phenomenon. Received July 18, 2000 Revised April 19, 2001  相似文献   

Sediment community metabolism associated with continental shelf hypoxia, Northern Gulf of Mexico   总被引：1，自引：0，他引：1  

Gilbert T. Rowe  Marta Elizabeth Cruz Kaegi  John W. Morse  Gregory S. Boland  Elva G. Escobar Briones 《Estuaries and Coasts》2002,25(6):1097-1106

Net fluxes of respiratory metabolites (O₂, dissolved inorganic carbon (DIC), NH₄ ⁺, NO₃ ^?, and NO₂ ^?) across the sediment-water interface were measured using in-situ benthic incubation chambers in the area of intermittent seasonal hypoxia associated with the Mississippi River plume. Sulfate reduction was measured in sediments incubated with trace levels of³⁵S-labeled sulfate. Heterotrophic remineralization, measured as nutrient regeneration, sediment community oxygen consumption (SOC), sulfate reduction, or DIC production, varied positively as a function of temperature. SOC was inversely related to oxygen concentration of the bottom water. The DIC fluxes were more than 2 times higher than SOC alone, under hypoxic conditions, suggesting that oxygen uptake alone cannot be used to estimate total community remineralization under conditions of low oxygen concentration in the water column. A carbon budget is constructed that compares sources, stocks, transformations, and sinks of carbon in the top meter of sediment. A comparison of remineralization processes within the sediments implicates sulfate reduction as most important, followed by aerobic respiration and denitrification. Bacteria accounted for more than 90% of the total community biomass, compared to the metazoan invertebrates, due presumably to hypoxic stress.  相似文献   

Crustal Thermal Structure of the Brazilian Equatorial Margin Using Fourier and Continuous Wavelet Transforms: A Comparative Analysis Based on Different Magnetic Datasets     

Herrera  Duvan Ricardo Herrera  de Castro  David Lopes  Oliveira  Jefferson Tavares Cruz  de Oliveira  Di&#;genes Cust&#;dio 《Surveys in Geophysics》2022,43(3):883-912

Surveys in Geophysics - In this work, we calculated the Curie Point Depth (CPD) for the Brazilian Equatorial Margin using the Fourier and continuous wavelet (CWT) transforms considering a linear...  相似文献   

Bedrock bedding,landsliding and erosional budgets in the Central European Alps   总被引：4，自引：0，他引：4       下载免费PDF全文

Fábio Cruz Nunes  Romain Delunel  Fritz Schlunegger  Naki Akçar  Peter W. Kubik 《地学学报》2015,27(5):370-378

We explore the controls of the litho‐tectonic architecture on the erosional flux in the 370‐km² Glogn basin (European Alps). In this basin, the bedding and schistosity of the bedrock dip parallel to the topographic slope on the NW valley flank, leading to a non‐dip slope situation on the opposite SE valley side. While the dip slope condition has promoted the occurrence of landslides (e.g. the c. 30‐km² deep‐seated Lumnezia landslide), the opposite non‐dip slope side of the valley hosts >100‐m‐deeply incised tributary streams. ¹⁰Be concentrations of stream sediments yield catchment‐averaged denudation rates that vary between 0.27 ± 0.03 and 2.19 ± 0.37 mm a^?1, while the spatially averaged denudation rate of the entire basin is 1.99 ± 0.34 mm a^?1. Our ¹⁰Be‐based approach reveals that the Lumnezia landslide front contributes c. 30–65% of the entire sediment budget, although it covers <5% of the Glogn basin. This suggests a primary control of the bedrock bedding on erosion rates and processes.  相似文献