Geology and paleomagnetism of El Potrero pluton, Baja California: Understanding criteria for timing of deformation and evidence of pluton tilt during batholith growth     

Gabriel Chvez Cabello  Roberto Molina Garza  Luis Delgado Argote  Rubn Contreras Flores  Elisa Ramírez  Amabel Ortega Rivera  Harald Bhnel  James Lee 《Tectonophysics》2006,424(1-2):1-17

The 102 Ma El Potrero pluton, in the western foothills of Sierra San Pedro Mártir, in north-central Baja California, was emplaced during a long period of contractional deformation bracketed between 132 and 85 Ma that affected this segment of the Peninsular Ranges Batholith. The pluton records regional and emplacement related deformation manifested by: (1) a solid-state fabric developed on its eastern contact, which is produced by eastward lateral pluton expansion; (2) cleavage triple point zones in the host-rock NW and SE of the pluton; (3) subhorizontal ductile shear zones indicative of top-to-the-east transport; (4) magmatic and tectonic foliations parallel to regional structural trends and regional shear zones; (5) variable axial ratios of microgranitoid enclaves close to pluton–wall rock contacts; (6) evidence of brittle-emplacement mechanisms in the western border of the pluton, which contrast with features indicating mainly ductile mechanisms toward the east; and, (7) markedly discordant paleomagnetic directions that suggest emplacement in an active tectonic setting. The overall mean for 9 accepted paleomagnetic sites is Dec = 34.6°, I = 25.7° (k = 88.3, α₉₅ = 5.5°), and is deviated  35° with respect to the reference cratonic direction. This magnetization is interpreted to indicate a combination of tilt due to initial drag during vertical diapiric ascent (or westward lateral-oblique expansion) of the adjacent San Pedro Mártir pluton and later rotation ( 15°) by Rosarito Fault activity in the southwest; this rotation may have occurred as eastward contraction acted to fill the space emptied by the ascending San Pedro Mártir pluton. The Rosarito fault may have tilted several plutons in the area (Sierra San Pedro Mártir, El Potrero, San José, and Encinosa). Magnetic susceptibility fabrics for 13 sites reflect mostly emplacement-related stress and regional stress. Paleomagnetic data and structural observations lead us to interpret the El Potrero pluton as a syntectonic pluton, emplaced within a regional shear zone delimited by the Main Mártir Thrust and the younger Rosarito Fault.  相似文献   

Looking North and South: Ideals and realities of inclusive environmental governance     

Ana Delgado  Roger Strand 《Geoforum》2010,41(1):144-153

This paper addresses the dynamics of real processes of inclusive environmental governance by looking at the decision-maker/expert/lay person interplay. Specifically, we present a comparative ethnographic study that leads to a critical examination of Marteen Hajer’s concept of technological citizenship and its role in normative models of so-called inclusive environmental governance. First, we present the Bionatur project of MST (Movimento Sem Terra/Landless People’s Movement), the largest rural movement in Latin America. The project explicitly attempts to include lay/traditional knowledge into the processes of defining and protecting a regulatory space for “Creole seeds”. Second, we describe the formally open and inclusive environmental management of polluted sediments during harbour dredging in Norway. In both cases the actors are confronted with difficult problems bound by contradictory constraints of the institutional and cultural contexts. In complex relationships, trust, dependency, responsibility and opposition, encompass the decision-maker/expert/lay interplay. Embedded in these contexts, it is not always clear that non-experts want full autonomy and responsibility. In complex relationships, trust, dependency, responsibility and opposition, encompass the decision-maker/expert/lay person interplay. The results suggest that ideals, if instantiated, are reshaped within concrete contexts of action. Participatory ideals such as “technological citizenship”, inclusiveness, transparency and accountability need not be relativised, but they would better be expressed as regulative norms for practice rather than ideals from which an acontextual model or structure may be deduced.  相似文献   

Bayesian lithology/fluid inversion—comparison of two algorithms   总被引：1，自引：0，他引：1  

Marit Ulvmoen  Hugo Hammer 《Computational Geosciences》2010,14(2):357-367

Algorithms for inversion of seismic prestack AVO data into lithology-fluid classes in a vertical profile are evaluated. The inversion is defined in a Bayesian setting where the prior model for the lithology-fluid classes is a Markov chain, and the likelihood model relates seismic data and elastic material properties to these classes. The likelihood model is approximated such that the posterior model can be calculated recursively using the extremely efficient forward–backward algorithm. The impact of the approximation in the likelihood model is evaluated empirically by comparing results from the approximate approach with results generated from the exact posterior model. The exact posterior is assessed by sampling using a sophisticated Markov chain Monte Carlo simulation algorithm. The simulation algorithm is iterative, and it requires considerable computer resources. Seven realistic evaluation models are defined, from which synthetic seismic data are generated. Using identical seismic data, the approximate marginal posterior is calculated and the exact marginal posterior is assessed. It is concluded that the approximate likelihood model preserves 50% to 90% of the information content in the exact likelihood model.  相似文献   

Practical aspects of demand and capacity evaluation of RC members in the context of EC8‐3     

Xavier Romo  Raimundo Delgado  Aníbal Costa 《地震工程与结构动力学》2010,39(5):473-499

The structural safety assessment procedures proposed in Part 3 of Eurocode 8 (EC8‐3) for the case of reinforced concrete structures are addressed. The practical evaluation of the member chord rotation demand according to EC8‐3 is examined in detail along with several alternative formulations. The need for these formulations is demonstrated by presenting example situations where the EC8‐3 proposal is difficult to apply. The effectiveness of the proposed approaches is assessed through an example application and recommendations for their practical use are defined. Given the importance of the shear span in this context, a sensitivity analysis of the EC8‐3 capacity models with respect to this parameter is carried out and discussed in a later section. This analysis aims to assess the validity of the simplifications proposed by a previous research study for the quantification of the EC8‐3 capacity values. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Can PAHs influence Cu accumulation by salt marsh plants?     

Almeida CM  Mucha AP  Delgado MF  Caçador MI  Bordalo AA  Vasconcelos MT 《Marine environmental research》2008,66(3):311-318

The presence of polycyclic aromatic hydrocarbons (PAHs) may change the mechanisms of metal uptake, thus influencing kinetics and extent of metal phytoextraction. Studies on the subject are scarce, particularly for salt marsh plants. The aim of this work was to investigate the effect of PAHs on the uptake of Cu by Halimione portulacoides, a plant commonly found in salt marshes. Experiments were carried out in the laboratory, either in hydroponics (sediment elutriate) or in sediment soaked in elutriate, which were prepared with sediment and water from a salt marsh of the Cavado river estuary (NW Portugal). Groups of H. portulacoides (grown in a greenhouse) were exposed to those media during six days. Cu(2+) (as Cu(NO(3))(2)), 10(2) and 10(4)mugl(-1), was added to the media as well as 1.6mugl(-1) of the sixteen EPA priority PAHs (0.1mugl(-1) of each PAHs). Cu was assayed in solutions, sediments and different plant tissues before and after experiments. After exposure, photosynthetic efficiency and levels of chlorophylls were also measured, indicating that plant stress indicators were identical in all plants independently of the media to which the plants were exposed. PAHs influenced both the soluble Cu fraction and Cu uptake by plants. The amounts of metal accumulated in both roots and stems were significantly higher when the 10(4)mugl(-1) of Cu enriched elutriate was amended with PAHs. Thus, results suggest that PAHs may modify Cu solubility, the Cu sorption by plants and/or the passive penetration of Cu into the root cells. Therefore, the combined effects of different types of pollutants should be taken in consideration when studying the remediation potential of plants, namely in terms of phytoextraction.  相似文献   

Preliminary paleolimnological study of rocha lagoon, SE Uruguay     

Felipe García-Rodríguez  Laura Del Puerto  Carola Castieira  Hugo Inda  Roberto Bracco  Peter Spechmann  Burkhard Wilhelm Scharf 《Limnologica》2001,31(3)

Physical, chemical and biological data from a sedimentary profile of Rocha lagoon (Uruguay) are presented. Analyses of silica remains showed that opal phytoliths, diatoms, sponge spicules and chrysophyte cysts were the most important contributors to biogenic silica. Organic matter, total nitrogen and total phosphorus were used to infer past trophic development. Physical analysis of sediments allowed us to identify five lithological units related to sea level variation and climatic events.  相似文献   

Planning Urban Growth in Ground Water Recharge Areas: Central Valley, Costa Rica     

Hugo Rodriguez-Estrada  Hugo A. Loaiciga 《Ground Water Monitoring & Remediation》1995,15(3):144-148

Nitrate levels in the ground water of the Central Valley of Costa Rica have increased in relation to the past. Previous studies determined that the unseweved sanitation systems in the recharge areas are the main source of nitrogen. Calculations are made in this study to estimate the maximum population density allowable without improved sewage systems in order to keep the nitrogen levels in ground water below the World Health Organization (WHO) criteria. Results were achieved employing a mass balance that involved the concentration and rate of domestic effluents and the flow rate in the aquifer, as well as an estimation of the effects caused by the agricultural activity. It was concluded that, in general terms, the population density must not exceed 45 inhabitants per hectare. Otherwise, sewage systems and treatment plants are necessary. These conclusions provide a basis for urban growth planning, which will protect ground water quality. The method used in this case should apply to similar situations.  相似文献   

Strange seismic attractor?     

Hugo Beltrami  Jean-Claude Mareschal 《Pure and Applied Geophysics》1993,141(1):71-81

Different time series were constructed from the data set containing all the seismic events recorded by the Parkfield network between 1969 and 1987. These series were analyzed to determine whether there exists an attractor in the phase space of the dynamical system characterizing seismic activity and to tentatively establish its dimension. The study has yielded ambiguous results. For all the time series analyzed, the dimension of the attractor appears higher than 12 and the correlation function of the seismic time series is undistinguishable from that of a series of random numbers of the same length. The lack of difference between the scaling parameters of two series suggests that, for all practical purposes, the seismic time series cannot be discriminated from a random series.  相似文献   

Dynamic modelling and design of earthquake-resistant walls     

Peter Linde  Hugo Bachmann 《地震工程与结构动力学》1994,23(12):1331-1350

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Magnetotelluric measurements at Eusebio,an equatorial station     

N.B. Trivedi  Elesbão G. de Souza  Eurico R. de Paula  J.M. da Costa  Hugo Fournier 《Physics of the Earth and Planetary Interiors》1981,25(3):241-244

Magnetotelluric measurements in the period range 100–86400 s were conducted at a coastal station under the equatorial electrojet (Eusebio, 3.87°S, 321.58°E). The magnetotelluric data were hand-scaled and analysed to obtain a scalar apparent resistivity profile at Eusebio. The depth of the intermediate conducting layer was found to be in the range 45–75 km and the final conducting layer seems to begin at a depth of about 350 km. Possible effects of the source field equatorial electrojet are discussed and our results are compared with those of an African station under the equatorial electrojet.  相似文献