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71.
Cristián Rodrigo Emilio Vera Antonio González-Fernández 《Journal of South American Earth Sciences》2009,27(1):1-10
Multi-channel seismic (MCS) reflection data recorded offshore from Valdivia (40° S), in the Chilean margin, were processed to obtain a seismic image to establish structural characteristics and relate them to the presence of the bottom-simulating reflector (BSR). Seismic structure velocity of the BSR was determined using 1-D forward modeling. Recorded seismograms for two representative common mid-point (CMP) gathers were compared with synthetics, using different physical parameters to fit the waveforms. Our results confirm the presence of gas hydrates above the BSR. The BSR spatial continuity appears to be either interrupted or irregular due to the presence of faults. Tectonic movements can change the gas hydrate stability zone and consequently the BSR disappears or becomes weaker. Structural and topographic factors, differences in concentration, vertical distribution characteristics and internal structure of gas hydrates can influence BSR amplitude behavior. Variability in the concentration, volume, and extra supply of free gas coming from faults could be the main factors in the change of BSR amplitudes. The inclusion of the attenuation factor in the modeling supports the existence of free gas below the BSR. It is possible that the free gas below the BSR is distributed in bubbles or “bags”. 相似文献
72.
Aquifer overexploitation: what does it mean? 总被引:9,自引:0,他引:9
Emilio Custodio 《Hydrogeology Journal》2002,10(2):254-277
Groundwater overexploitation and aquifer overexploitation are terms that are becoming common in water-resources management.
Hydrologists, managers and journalists use them when talking about stressed aquifers or some groundwater conflict. Overexploitation
may be defined as the situation in which, for some years, average aquifer abstraction rate is greater than, or close to the
average recharge rate. But rate and extent of recharge areas are often very uncertain. Besides, they may be modified by human
activities and aquifer development. In practice, however, an aquifer is often considered as overexploited when some persistent
negative results of aquifer development are felt or perceived, such as a continuous water-level drawdown, progressive water-quality
deterioration, increase of abstraction cost, or ecological damage. But negative results do not necessarily imply that abstraction
is greater than recharge. They may be simply due to well interferences and the long transient period that follow changes in
the aquifer water balance. Groundwater storage is depleted to some extent during the transient period after abstraction is
increased. Its duration depends on aquifer size, specific storage and permeability. Which level of "aquifer overexploitation"
is advisable or bearable, depends on the detailed and updated consideration of aquifer-development effects and the measures
implemented for correction. This should not be the result of applying general rules based on some indirect data. Monitoring,
sound aquifer knowledge, and calculation or modelling of behaviour are needed in the framework of a set of objectives and
policies. They should be established by a management institution, with the involvement of groundwater stakeholders, and take
into account the environmental and social constraints. Aquifer overexploitation, which often is perceived to be associated
with something ethically bad, is not necessarily detrimental if it is not permanent. It may be a step towards sustainable
development. Actually, the term aquifer overexploitation is mostly a qualifier that intends to point to a concern about the
evolution of the aquifer-flow system in some specific, restricted points of view, but without a precise hydrodynamic meaning.
Implementing groundwater management and protection measures needs quantitative appraisal of aquifer evolution and effects
based on detailed multidisciplinary studies, which have to be supported by reliable data.
Electronic Publication 相似文献
73.
The analysis of series of climatic values for almost a millennium, obtained by dendroclimatic methods, makes evident the existence of values that are remarkably greater or smaller than the rest. The criterion to identify this type of values has been the distance to the mean of the climatic series, in units of the standard deviation: out-of-range values are those that differ from the mean in more than four standard deviations. The study of these values gives an original perspective of the climatic past in Spain, including the outstanding oscillations of the Little Ice Age (LIA). The unusual climatic conditions of the last decades are also detected using this method. 相似文献
74.
Antonio Geraldo Ferreira Emilio Soria-Olivas Antonio Jos�� Serrano L��pez Ernesto Lopez-Baeza 《Theoretical and Applied Climatology》2011,106(1-2):263-279
This study describes the results of artificial neural network (ANN) models to estimate net radiation (R n), at surface. Three ANN models were developed based on meteorological data such as wind velocity and direction, surface and air temperature, relative humidity, and soil moisture and temperature. A comparison has been made between the R n estimates provided by the neural models and two linear models (LM) that need solar incoming shortwave radiation measurements as input parameter. Both ANN and LM results were tested against in situ measured R n. For the LM ones, the estimations showed a root mean square error (RMSE) between 34.10 and 39.48?W?m?2 and correlation coefficient (R 2) between 0.96 and 0.97 considering both the developing and the testing phases of calculations. The estimates obtained by the ANN models showed RMSEs between 6.54 and 48.75?W?m?2 and R 2 between 0.92 and 0.98 considering both the training and the testing phases. The ANN estimates are shown to be similar or even better, in some cases, than those given by the LMs. According to the authors?? knowledge, the use of ANNs to estimate R n has not been discussed earlier, and based on the results obtained, it represents a formidable potential tool for R n prediction using commonly measured meteorological parameters. 相似文献
75.
Francisco J. Alcalá Yolanda Cantón Sergio Contreras Ana Were Penélope Serrano-Ortiz Juan Puigdefábregas Albert Solé-Benet Emilio Custodio Francisco Domingo 《Environmental Earth Sciences》2011,62(3):541-557
In the high-permeability, semiarid carbonate aquifer in the Sierra de Gádor Mountains (southeastern Spain), some local springs
draining shallow perched aquifers were of assistance in assessing applicability of the atmospheric chloride mass balance (CMB)
for quantifying total yearly recharge (R
T) by rainfall. Two contrasting hydrological years (October through September) were selected to evaluate the influence of climate
on recharge: the average rainfall year 2003–2004, and the unusually dry 2004–2005. Results at small catchment scale were calibrated
with estimated daily stand-scale R
T obtained by means of a soil water balance (SWB) of rainfall, using the actual evapotranspiration measured by the eddy covariance
(EC) technique. R
T ranged from 0.35 to 0.40 of rainfall in the year, with less than a 5% difference between the CMB and SWB methods in 2003–2004.
R
T varied from less than 0.05 of rainfall at mid-elevation to 0.20 at high elevation in 2004–2005, with a similar difference
between the methods. Diffuse recharge (R
D) by rainfall was quantified from daily soil water content field data to split R
T into R
D and the expected concentrated recharge (R
C) at catchment scale in both hydrological years. R
D was 0.16 of rainfall in 2003–2004 and 0.01 in 2004–2005. Under common 1- to 3-day rainfall events, the hydraulic effect of
R
D is delayed from 1 day to 1 week, while R
C is not delayed. This study shows that the CMB method is a suitable tool for yearly values complementing and extending the
more widely used SWB in ungauged mountain carbonate aquifers with negligible runoff. The slight difference between R
T rates at small catchment and stand scales enables results to be validated and provides new estimates to parameterize R
T with rainfall depth after checking the weight of diffuse and concentrated mechanisms on R
T during moderate rainfall periods and episodes of marked climatic aridity. 相似文献
76.
Edoardo Barbero Luca Pandolfi Morteza Delavari Asghar Dolati Emilio Saccani Rita Catanzariti Valeria Luciani Marco Chiari Michele Marroni 《地学前缘(英文版)》2021,12(3):101106
The Durkan Complex is a key tectonic element of the Makran accretionary prism (SE Iran) and it has been interpreted as representing a continental margin succession. We present here a multidisciplinary study of the western Durkan Complex, which is based on new geological, stratigraphic, biostratigraphic data, as well as geochemical data of the volcanic and meta-volcanic rocks forming this complex. Our data show that this complex consists of distinct tectonic slices showing both non-metamorphic and very low-grade metamorphic deformed successions. Stratigraphic and biostratigraphic data allow us to recognize three types of successions. Type-I is composed by a Coniacian – early Campanian pelagic succession with intercalation of pillow lavas and minor volcaniclastic rocks. Type-II succession includes a volcanic sequence passing to a volcano-sedimentary sequence with Cenomanian pelagic limestones, followed by a hemipelagic sequence. This succession is characterized by abundant mass-transport deposits. Type-III succession includes volcanic and volcano-sedimentary sequences, which are stratigraphically covered by a Cenomanian platform succession. The latter is locally followed by a hemipelagic sequence. The volcanic rocks in the different successions show alkaline geochemical affinity, suggesting an origin from an oceanic within-plate setting. Our new results indicate that the western Durkan Complex represents fragments of seamounts tectonically incorporated in the Makran accretionary wedge during the latest Late Cretaceous–Paleocene. We propose that incorporation of seamounts in the frontal prism caused a shortening of the whole convergent margin and possibly contributed to controlling the deformation style in the Makran Accretionary Wedge during Late Cretaceous–Paleocene times. 相似文献
77.
Vincent E. A. Post Gualbert Oude Essink Adam Szymkiewicz Mark Bakker Georg Houben Emilio Custodio Clifford Voss 《Hydrogeology Journal》2018,26(6):1767-1770
The Salt Water Intrusion Meetings, or SWIMs, are a series of meetings that focus on seawater intrusion in coastal aquifers and other salinisation processes. 2018 marks the 50th year of the SWIM and the 25th biennial meeting. The SWIM proceedings record half a century of research progress on site characterisation, geophysical and geochemical techniques, variable-density flow, modelling, and water management. The SWIM is positioning itself to remain a viable platform for discussing the coastal aquifer management challenges of the next 50 years. 相似文献
78.
The causes of land-use and land-cover change: moving beyond the myths 总被引:39,自引:0,他引:39
Eric F. Lambin B. L. Turner Helmut J. Geist Samuel B. Agbola Arild Angelsen John W. Bruce Oliver T. Coomes Rodolfo Dirzo Günther Fischer Carl Folke P. S. George Katherine Homewood Jacques Imbernon Rik Leemans Xiubin Li Emilio F. Moran Michael Mortimore P. S. Ramakrishnan John F. Richards Helle Sknes Will Steffen Glenn D. Stone Uno Svedin Tom A. Veldkamp Coleen Vogel Jianchu Xu 《Global Environmental Change》2001,11(4)
Common understanding of the causes of land-use and land-cover change is dominated by simplifications which, in turn, underlie many environment-development policies. This article tracks some of the major myths on driving forces of land-cover change and proposes alternative pathways of change that are better supported by case study evidence. Cases reviewed support the conclusion that neither population nor poverty alone constitute the sole and major underlying causes of land-cover change worldwide. Rather, peoples’ responses to economic opportunities, as mediated by institutional factors, drive land-cover changes. Opportunities and constraints for new land uses are created by local as well as national markets and policies. Global forces become the main determinants of land-use change, as they amplify or attenuate local factors. 相似文献
79.
Artyom V. Astashenok Emilio Elizalde Jaume de Haro Sergei D. Odintsov Artyom V. Yurov 《Astrophysics and Space Science》2013,347(1):1-13
Several simple dark energy models on the brane are investigated. They are compared with corresponding models in the frame of 4d Friedmann-Robertson-Walker cosmology. For constraining the parameters of the models considered, recent observational data, including SNIa apparent magnitude measurements, baryon acoustic oscillation results, Hubble parameter evolution data and matter density perturbations are used. Also, explicit formulas of the so-called state-finder parameters in teleparallel theories are found that could be useful to test these models and compare Loop Quantum Cosmology and Brane Cosmology. The conclusion is reached that a joint analysis as the one developed here allows to estimate, in a very clear way, possible deviation of our cosmology from the standard Friedmann-Robertson-Walker one. 相似文献
80.
Emilio Santos 《Astrophysics and Space Science》2012,341(2):411-416
A gravity theory is considered with the Einstein-Hilbert Lagrangean R+aR 2+bR μν R μν , R μν being Ricci’s tensor and R the curvature scalar. The parameters a and b are taken of order 1 km2. Arguments are given which suggest that the effective theory so obtained might be a fair approximation of a viable theory. A numerical integration is performed of the field equations for a free neutron gas. The result is that the star mass increases with increasing central density until about 1 solar mass and then decreases. The baryon number increases monotonically, which suggests that the theory allows stars in equilibrium with arbitrary baryon number, no matter how large. 相似文献