A zone of mylonite and related ductile deformation beneath the alpujarride nappe complex,betic cordilleras,S. Spain

A zone of mylonite is commonly developed beneath the Alpujarride nappe complex. The contact with the underlying Nevado-Filabride Complex is marked by a zone of calc mylonite, dolomitic breccia, iron-rich carbonate rocks, and marble. These lie on a thin zone of ultramylonite derived from Nevado-Filabride schist. Related ductile deformation decreases downwards, but may extend up to 400 m beneath the contact. This deformation produces a characteristic platy foliation, a strong elongation lineation, and a proto-mylonitic microstructure. Kinematic analysis of these rocks may help determine the direction of nappe transport.Mylonitic or protomylonitic microstructures are not developed in the Alpujarride rocks, although these are strongly deformed adjacent to the contact. Microstructural evidence suggests that deformation occurred by pressure-solution in these rocks, and not by the crystal-plastic processes that operated in the Nevado-Filabride protomylonitic schists.

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Zusammenfassung Im Liegenden des Deckengebäudes der Alpujarriden findet sich an vielen Stellen eine Mylonitzone. Der Kontakt mit den unterlagernden nevado-filabriden Gesteinen ist durch Kalkmylonite, Dolomitbrekzien, eisenreiche Karbonate und Marmore markiert. Diese liegen auf einer dünnen Zone von Ultramylonit, der sich aus nevado-filabriden Glimmerschiefern entwickelt hat. Diese plastische Verformung nimmt zum Liegenden hin ab, kann aber bis zu 400 m unterhalb des Deckenkontaktes reichen. Sie erzeugt eine charakteristische, plattige Schieferung, eine stark ausgeprägte Streckungslineation und eine protomylonitische Mikrostruktur. Mit einer kinematischen Analyse dieser Gesteine kann die Transportrichtung der Deckeneinheiten bestimmt werden.Die Glimmerschiefer und Phyllite alpujarrider Zuordnung besitzen keine mylonitische Mikrostruktur, obwohl sie stark deformiert sind. Dies deutet darauf hin, daß, im Gegensatz zum intrakristallinen Gleiten in den nevado-filabriden Protomyloniten, vor allem Drucklösung als Deformationsmechanismus anzusehen ist.

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Resumen Bajo el complejo de mantos de los Alpujárrides se observa comunmente el desarrollo de una zona milonitica. El contacto de dicho complejo con el de Nevado-Filabride está señalado por una zona de calcomilonitas, brechas dolomiticas, rocas carbonatadas ricas en hierro y mármoles. Estos se situan en una zona estrecha de ultramilonitas que se derivan de los esquistos del Nevado-Filabride, La deformación dúctil asociada decrece en sentido descendente, pero puedo extenderse hasta 400 m por debajo del contacto. Esta deformation produce una foliación planar characterística, una lineación de extensión muy pronunciada y una microestructura protomilonítica. Los análisis cinemáticos de éstas rocas pueden ayudar a determinar la dirección de transporte de los mantos.Las microestructuras miloníticas y protomyloníticas no se desarrollan en las rocas Alpujárrides, aunque dichas rocas están fuertemente deformadas junto al contacto. Las observaciones microestructurales sugieren que la deformación tuvo lugar por «pressure-solution» y no por procesos de plasticidad cristalina como los operantes en los esquistos protomiloníticos del Nevado-Filabride.

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Geometrical relationships between unconformities and subsequent folding: the Arro fold system (southern Pyrenees)Relations entre discordances et plissement dans le système de plis et chevauchements d'Arro (bassin de Graus-Tremp,Pyrénées)

The Arro system is an oblique fold system involving the Eocene sediments of the Graus-Tremp basin. It consists of westward-verging folds, trending NNW–SSE, some of them related with thrusts, in piggyback sequence. Seismic profiles allow to infer the geometry of structures at depth: folds and thrusts are ‘decolled’ over an unconformity between turbiditic and platform sediments. Re-activation of bedding surfaces by folding in the underlying units resulted in folding and thrusting in the upper series. To cite this article: A.M. Casas et al., C. R. Geoscience 334 (2002) 765–772.     

Geophysical investigations in the El-Wad Cave,MT. Carmel,Israel

Measurements of the thickness of the sediment fill in the el-Wad Cave, Mt. Carmel, Israel were carried out using seismic refraction methods. The cave is one of the famous Mt. Carmel Caves, where finds of Mousterian to Natufian prehistoric cultures had been encountered. The survey discovered a series of karstic pits in several chambers in the cave, with good correlation between the dimension of the chambers and the thickness of the sediment fill. The deepest pit was found in the inner part of the cave, where the oldest archaeological material could be expected.     

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

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.     

Mapping Groundwater Potential Through an Ensemble of Big Data Methods

Groundwater resources are crucial to safe drinking supplies in sub-Saharan Africa, and will be increasingly relied upon in a context of climate change. The need to better understand groundwater calls for innovative approaches to make the best out of the existing information. A methodology to map groundwater potential based on an ensemble of machine learning classifiers is presented. A large borehole database (n = 1848) was integrated into a Geographic Information Systems (GIS) environment and used to train, validate and test 12 machine learning algorithms. Each classifier predicts a binary target (positive or negative borehole) based on the minimum flow rate required for communal domestic supplies. Classification is based on a number of explanatory variables, including landforms, lineaments, soil, vegetation, geology and slope, among others. Correlations between the target and explanatory variables were then generalized to develop groundwater potential maps. Most algorithms attained success rates between 80% and 96% in terms of test score, which suggests that the outcomes provide an accurate picture of field conditions. Statistical learners were observed to perform better than most other algorithms, excepting random forests and support vector machines. Furthermore, it is concluded that the ensemble approach provides added value by incorporating a measure of uncertainty to the results. This technique may be used to rapidly map groundwater potential for rural supply or humanitarian emergencies in areas where there is sufficient historical data but where comprehensive field work is unfeasible.     

Estimates of Horizontal Groundwater Flow Velocities in Boreholes

Currently, monitoring tools can be deployed in observation boreholes to better assess groundwater flow, flux of dissolved contaminants and their mass discharge in an aquifer. The relationship between horizontal water velocity in observation boreholes and Darcy fluxes in the surrounding aquifer has been studied for natural flow conditions (i.e., no pumping). Interpretation of measurements taken with dilution tests, the colloidal borescope, the Heat Pulse Flowmeter, and other techniques require the conversion of observed borehole velocity u to aquifer Darcy flux q_∞ . This conversion is typically done through a proportionality factor α = u/q_∞ . In experimental studies as well as in theoretical developments, reported values of α vary almost three orders of magnitude (from 0.5 to 10). This large variability in reported values of α could be explained by: (1) unclear distinction between Darcy flux and water seepage velocity, (2) unclear definition of water velocity in the borehole, (3) effects of well screen and the presence of the measurement device itself on the observable velocities, and (4) hydraulic conditions in the borehole annulus. We address (1), (2) from a conceptual/theoretical perspective, and (3) by means of numerical simulations. We show that issue (1) in low porosity aquifers can yield to order-of-magnitude discrepancies in estimates of q_∞ ; (2) may result in discrepancies of up to 50%, and (3) can cause differences up to 20% of water velocity in the borehole void space compared to the theoretical case of an open borehole.     

Bedrock geology controls on catchment storage,mixing, and release: A comparative analysis of 16 nested catchments

The bedrock controls on catchment mixing, storage, and release have been actively studied in recent years. However, it has been difficult to find neighbouring catchments with sufficiently different and clean expressions of geology to do comparative analysis. Here, we present new data for 16 nested catchments (0.45 to 410 km²) in the Alzette River basin (Luxembourg) that span a range of clean and mixed expressions of schists, phyllites, sandstones, and quartzites to quantify the relationships between bedrock permeability and metrics of water storage and release. We examined 9 years' worth of precipitation and discharge data, and 6 years of fortnightly stable isotope data in streamflow, to explore how bedrock permeability controls (a) streamflow regime metrics, (b) catchment storage, and (c) isotope response and catchment mean transit time (MTT). We used annual and winter precipitation–run‐off ratios, as well as average summer and winter precipitation–run‐off ratios to characterise the streamflow regime in our 16 study catchments. Catchment storage was then used as a metric for catchment comparison. Water mixing potential of 11 catchments was quantified via the standard deviation in streamflow δD (σδD) and the amplitude ratio (A_S/A_P) of annual cycles of δ¹⁸O in streamflow and precipitation. Catchment MTT values were estimated via both stable isotope signature damping and hydraulic turnover calculations. In our 16 nested catchments, the variance in ratios of summer versus winter average run‐off was best explained by bedrock permeability. Whereas active storage (defined here as a measure of the observed maximum interannual variability in catchment storage) ranged from 107 to 373 mm, total catchment storage (defined as the maximum catchment storage connected to the stream network) extended up to ~1700 mm (±200 mm). Catchment bedrock permeability was strongly correlated with mixing proxies of σδD in streamflow and δ¹⁸O A_S/A_P ratios. Catchment MTT values ranged from 0.5 to 2 years, based on stable isotope signature damping, and from 0.5 to 10 years, based on hydraulic turnover.     

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

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.     

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

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.