Zur Stratigraphie des Altpaläozoikums in Argentinien     

Prof. Dr. Alfredo J. Cuerda 《International Journal of Earth Sciences》1974,63(3):1261-1277

At the beginning of the Paleozoic era three geotectonic units were already constitued in the argentine territory: 1. central cratonic region; 2. ortogeosynclinal belt in the West, and 3. intracratonic region in the East. On the basis of the morphostructural units that emerge out of the development of the geotectonic pattern, the regional distribution and stratigraphy of the Lower Paleozoic rocks are described (Cambrian to Silurian). In the Northern Argentina (Subandine ranges, Eastern Cordillera and Puna) the stratigraphical sequence is complete with a thickness of 9.100 meters. In the Transpampean Ranges only the Ordovician (Tremadoc-Llanvirn) is represented with a minimum thickness of 3.850 meters. In the Precordillera of Western Argentina the sequence is complete with a minimum thickness of 6.000 meters, the Ordovician being the most developed. In the San Rafael ranges (Mendoza), the Northern and Southern ranges of the Buenos Aires province, the Northpatagonian nesocraton and the Chaco-Parana basin, the succession is incomplete or little known. In each case the recognized lithological units are described and their respective stratigraphical relations are indicated.  相似文献   

Geological and morphological study of the Jiufengershan landslide triggered by the Chi-Chi Taiwan earthquake   总被引：2，自引：4，他引：2  

Kuo-Jen Chang  Alfredo Taboada  Yu-Chang Chan 《Geomorphology》2005,71(3-4):293-309

The Jiufengershan rock and soil avalanche is one of the largest landslides triggered by the Chi-Chi earthquake Taiwan 1999. The landslide destabilized the western limb of the Taanshan syncline along a weak stratigraphic layer. It involved a flatiron remnant, which was almost entirely mobilized during the earthquake. The avalanche was slowed down by NS trending ridges located downstream along the Jiutsaihu creek. The landslide affected a 60 m thick and 1.5 km long sedimentary pile composed of shales and sandstones, which dip 22°SE toward a transverse valley. The triggering mechanism and the sliding process were analyzed by means of geological and morphological data from aerial photographs and observed in the field. A high-resolution airborne Light Detection and Ranging (LiDAR) image taken 2.5 years after the landslide allows the identification of morphological structures along the sliding surface and the landslide accumulation. The sliding surface shows several deformation structures such as fault scarps and folds. These structures are interpreted in terms of basal shear stresses created during the avalanche. Three major joint sets were identified at the sliding surface. The isopach map of the landslide was calculated from the comparison between elevation models before and after the earthquake. The coseismic volume of mobilized material and landslide deposit data are 42 × 10⁶ m³ and 50 × 10⁶ m³, respectively. The geometry of the landslide accumulation in the field has an irregular star shape. The morphology of the deposit area shows a sequence of smooth reliefs and depressions that contrast with the neighboring ridges.  相似文献   

Status of an endangered subspecies: the peninsular pronghorn at Baja California     

Jorge Cancino  Alfredo Ortega-Rubio  Jos A. Sanchez-Pacheco 《Journal of Arid Environments》1996,32(4):463-467

During November 1993, we traversed by ground and by air the Vizcaíno Desert, the last redoubt of the peninsular pronghorn (Antilocapra americana peninsularis). A total of 29 h of aerial census was performed and a total of 1900 km²were covered by ground, totalling 400 man hours of survey. At present the peninsular pronghorn population consists of 175 individuals, and inhabits an area of approximately 5000 km². Because of the impossibility of controlling its activities over such an area and because of the present small population size, we propose to manage part of the population in semi-captivity at Mesa de la Choya island, with the objective of assuring the survival of this subspecies, the most endangered mammal in Mexico.  相似文献   

Seismic response and energy dissipation of 3D complex steel buildings considering the influence of interior semi-rigid connections: low- medium- and high-rise     

Alfredo Reyes-Salazar  José M. Sauceda-Pimentel  Sonia E. Ruiz  Edén Bojórquez  Juan Bojorquez 《Bulletin of Earthquake Engineering》2018,16(11):5557-5590

A numerical investigation regarding the seismic behavior of complex-3D steel buildings with perimeter moment resisting frames (PMRF) and interior gravity frames (GF) is conducted. The interior connections are assumed to be first perfectly pinned (PP) and then semi-rigid (SR); the two model responses are compared. Three steel building models representing low-, medium- and high-rise buildings, and several strong motions are used. The relative stiffness of SR connections is calculated according to the Richard Model and the Beam Line Theory. The Ruaumoko Computer Program is used to perform the required step-by-step nonlinear seismic analysis. Results indicate that interstory shears and interstory displacements at PMRF may be significantly reduced when interior connections are modeled as SR. Average reductions of up to 20, 46 and 11% are observed for interstory shears, for low-, medium-, and high-rise buildings, respectively. The corresponding reductions for interstory displacements are about 14, 44 and 15%. The contribution of GF to the lateral resistance is considerable, which significantly increases when the connections are modeled as SR; relative contributions larger than 80% are observed. The dissipated energy (DE) at PMRF is larger for the buildings with PP than for the buildings with SR connections indicating that damage at PMRF is reduced. Thus, the effect of the stiffness and the DE at interior connections should not be ignored. However, the design of some elements, particularly columns of the GF, has to be revised; these members may not be able to support the loads produced by the neglected lateral contribution if they are not properly designed.  相似文献   

Phytoremediation Potential of Jack Bean Plant for Multi‐Element Contaminated Soils From Ribeira Valley,Brazil          下载免费PDF全文

Maíra da Silva  Sara Adrián López de Andrade  Alfredo Borges De‐Campos 《洁净——土壤、空气、水》2018,46(6)

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Dynamics and seismic performance of rocking bridges accounting for the abutment-backfill contribution     

Ioannis M. Thomaidis  Andreas J. Kappos  Alfredo Camara 《地震工程与结构动力学》2020,49(12):1161-1179

The present study explores analytically the concept of rocking isolation in bridges considering for the first time the influence of the abutment-backfill system. The dynamic response of rocking bridges with free-standing piers of same height and same section is examined assuming negligible deformation for the substructure and the superstructure. New relationships for the prediction of the bridge rocking motion are derived, including the equation of motion and the restitution coefficient at each impact at the rocking interfaces. The bridge structure is found to be susceptible to a failure mode related to the failure of the abutment-backfill system, which can occur prior to the well-known overturning of the rocking piers. Thus, a new failure spectrum is proposed called Failure Minimum Acceleration Spectrum (FMAS) which extends the overturning spectrum put forward in previous studies, and it differs in principle from the latter. The comparison with the dynamic response of bridges modelled as rocking frames without abutments reveals not only that seat-type abutments and their backfill have a generally beneficial effect on the seismic performance of rocking pier bridges by suppressing the free rocking motion of the frame system, but also that the simple frame model cannot capture all salient features of the rocking bridge response as it misses potential failure modes, overestimating the rocking bridge's safety when these modes are critical.  相似文献   

Forecasting annual precipitation to improve the operation of dams in the Comahue region,Argentina     

Paula Elisa Romero  Alfredo Luis Rolla  Fernando Losano 《水文科学杂志》2020,65(11):1974-1983

ABSTRACT

This paper attempts to design statistical models to forecast annual precipitation in the Neuquen and Limay river basins in the Comahue region of Argentina. These forecasts are especially useful as they are used to better organize the operation of hydro-electric dams, the agriculture in irrigated valleys and the safety of the population. In this work, multiple linear regression statistical models are built to forecast mean annual rainfall over the two river basins. Since the maximum precipitation occurs in the winter (June–August), forecasting models have been developed for the beginning of March and for the beginning of June, just before the rainy season starts. The results show that the sea-surface temperatures of the Indian and Pacific oceans are good predictors for March models and explain 42.8% of the precipitation index variance. The efficiency of the models increases in June, adding more predictors related to the autumn circulation.  相似文献   

Effects of basement structural and stratigraphic heritages on volcano behaviour and implications for human activities （the IGCP project 455）     

Alessandro Tibaldi Alfredo Mahar F. A. Lagmaye Vera V. Ponomareva 《《幕》》2005,28(3):158-170

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Spatial Analysis of Airborne Geophysical Data Applied to Geological Mapping and Mineral Prospecting in the Serra Leste Region, Carajás Mineral Province, Brazil     

Carlos Roberto de Souza Filho  Alfredo Rossetto Nunes  Emilson Pereira Leite  Lena Virgínia Soares Monteiro  Roberto Perez Xavier 《Surveys in Geophysics》2007,28(5-6):377-405

The Serra Leste region, located in the northeast portion of Carajás Mineral Province (PA), hosts important chrome-PGE, Au–Pd–Pt, Cu–Mo–Au, iron, and manganese deposits and occurrences related to different geological settings. We present a regional prospective model with focus on PGE mineralizations based on airborne geophysics (magnetometry, gamma-ray spectrometry and time domain electromagnetometry) and geological data. Geological and geophysics data analysis indicate a plausible correspondence between areas with meta-mafic–ultramafic rocks and low values in gamma spectrometry, mainly for the thorium channel. The meta-ultramafic units of the complexes, the main host rock of the PGE mineralization, are well defined by analytic signal from the anomalous magnetic field and by the apparent conductance anomalies derived from the GEOTEM system. The combination of the derivative products with updated geological data of the Serra Leste region and PGE-Luanga deposit enable to establish a regional prospective model for PGE and the identification of new targets within the studied area.  相似文献   

Contrasting hydrothermal activity at Sierra Negra and Alcedo volcanoes, Galapagos Archipelago, Ecuador     

Fraser Goff  Gary M. McMurtry  Dale Counce  James A. Simac  Alfredo R. Roldán-Manzo  David R. Hilton 《Bulletin of Volcanology》2000,62(1):34-52

2 and approximately 85% SO₂ of the total sulfur gas. Relative amounts of He, Ar, and N₂ show a distinct hot-spot signature ( ). The δ¹³C–CO₂ is approximately −3.6‰ and δ³⁴S_T is approximately +3.3‰. The δD/δ¹⁸O of fumarole H₂O indicates steam separation from local meteoric waters whose estimated minimum mean residence time from ³H analyses is ≤40 years. Fumarolic activity at Alcedo is controlled by a caldera-margin fault containing at least seven hydrothermal explosion craters, and by an intracaldera rhyolite vent. Two explosion craters which formed in 1993–1994 produce approximately 15 m³/s of steam, yet discharge temperatures are ≤97°C. Water content of the total gas is 95–97 mol.%, noncondensible gas is 92–98 mol.% CO₂, and sulfur gas is dominated by H₂S. Relative amounts of He, Ar, and N₂ show extensive mixing between hot spot and air or air-saturated meteoric water components but the average . The δ¹³C–CO₂ is approximately −3.5‰ and δ³⁴S_T is approximately −0.8‰. The δD/δ¹⁸O of fumarole steam indicates separation from a homogeneous reservoir that is enriched 3–5‰ in ¹⁸O compared with local meteoric water. ³H indicates that this reservoir water has a maximum mean residence time of approximately 400 years and empirical gas geothermometry indicates a reservoir temperature of 260–320°C. The intracaldera hydrothermal reservoir in Alcedo is probably capable of producing up to 150 MW; however, environmental concerns as well as lack of infrastructure and power users will limit the development of this resource. Received: 19 April 1999 / Accepted: 23 October 1999  相似文献