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1.
A model is proposed describing the mechanical evolution of a shear zone along compressional and extensional plate boundaries, subject to constant strain rate. The shear zones are assumed as viscoelastic with Maxwell rheology and with elastic and rheological parameters depending on temperature and petrology. Stress and strain are computed as functions of time and depth. For both kinds of boundaries the model reproduces the existence of a shallow seismogenic zone, characterized by a stress concentration. The thickness of the seismogenic layer is evaluated considering the variations of shear stress and frictional strength on faults embedded in the shear zone. Assuming that a fault dislocation takes place, the brittle-ductile transition is assumed to occur at the depth at which the time derivative of total shear stress changes from positive to negative values. The effects of different strain rates and geothermal gradients on the depth of the brittle-ductile transition are studied. The model predictions are consistent with values inferred from seismicity data of different boundary zones. 相似文献
2.
By means of a 2D finite‐element procedure, we tested how heterogeneities at the scale of seismogenic fault affect the displacement. We defined one or more slip distributions for two typical normal‐faulting earthquakes in the Central Apennines, computed the displacement occurred within different structures including lateral heterogeneities, and compared the different displacement profiles to isolate the effect of the crustal structure. To understand at what magnitude the heterogeneities affect the observation significantly, we compared the predicted coseismic displacement with GPS and DInSAR data for the Colfiorito 1997 earthquake. We find that heterogeneities significantly affect the observable horizontal coseismic displacement for the larger magnitudes, whereas for smaller quakes, they affect horizontal displacement close to the fault trace only. 相似文献
3.
Measuring and modeling vertical gradients in suspended sediments in the Solimões/Amazon River 
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下载免费PDF全文 E. Armijos A. Crave R. Espinoza P. Fraizy A.L.M.R. Dos Santos F. Sampaio E. De Oliveira W. Santini J.M. Martinez P. Autin N. Pantoja M. Oliveira N. Filizola 《水文研究》2017,31(3):654-667
Accurately measuring sediment flux in large rivers remains a challenge due to the spatial and temporal cross‐sectional variability of suspended sediment concentrations in conjunction with sampling procedures that fail to accurately quantify these differences. This study presents a field campaign methodology that can be used to improve the measurement of suspended sediment concentrations in the Amazon River or similarly large rivers. The turbidity signal and Rouse model are together used in this study to define the spatial distribution of suspended sediment concentrations in a river cross‐section, taking into account the different size fractions of the sediment. With this methodology, suspended sediment fluxes corresponding to each sediment class are defined with less uncertainty than with manual samples. This paper presents an application of this methodology during a field campaign at different gauging stations along a 3,000‐km stretch of the Solimões/Amazon River during low water and flood periods. Vertical concentration profiles and Rouse model applications for distinctive sediment sizes are explored to determine concentration gradients throughout a cross‐section of the river. The results show that coupling both turbidity technology and the Rouse model may improve our understanding of the spatial distribution of different sediments fractions sizes in the Solimões/Amazon River. These data are very useful in defining a pertinent monitoring strategy for suspended sediment concentrations in the challenging context of large rivers. 相似文献
4.
Dai Jie Tang Hongzhi Li Xuegong Santini Claire-Lise Cui Wenpeng Liu Na Qi Xiaoqing Cui Xuehua Grossi Alain Notareschi Philippe Zhang Wei-Jia Wu Long-Fei 《中国海洋湖沼学报》2021,39(1):297-305
Journal of Oceanology and Limnology - Resazurin (RZ) is a weakly fluorescent blue dye and can be reduced irreversibly to highly fluorescent pink resorufin (RF) that is reduced reversibly to... 相似文献
5.
Gerardo Severino Alessandro Santini Angelo Sommella 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(4):567-582
Average steady source flow in heterogeneous porous formations is modelled by regarding the hydraulic conductivity K(x) as a stationary random space function (RSF). As a consequence, the flow variables become RSFs as well, and we are interested into calculating their moments. This
problem has been intensively studied in the case of a Neumann type boundary condition at the source. However, there are many
applications (such as well-type flows) for which the required boundary condition is that of Dirichlet. In order to fulfill
such a requirement the strength of the source must be proportional to K(x), and therefore the source itself results a RSF. To solve flows driven by sources whose strength is spatially variable, we
have used a perturbation procedure similar to that developed by Indelman and Abramovich (Water Resour Res 30:3385–3393, 1994) to analyze flows generated by sources of deterministic strength. Due to the linearity of the mathematical problem, we have
focused on the explicit derivation of the mean head distribution G
d
(x) generated by a unit pulse. Such a distribution represents the fundamental solution to the average flow equations, and it
is termed as mean Green function. The function G
d
(x) is derived here at the second order of approximation in the variance σ2 of the fluctuation (where K
A
is the mean value of K(x)), for arbitrary correlation function ρ(x), and any dimensionality d of the flow domain. We represent G
d
(x) as product between the homogeneous Green function G
d
(0)(x) valid in a domain with constant K
A
, and a distortion term Ψ
d
(x) = 1 + σ2ψ
d
(x) which modifies G
d
(0)(x) to account for the medium heterogeneity. In the case of isotropic formations ψ
d
(x) is expressed via one quadrature. This quadrature can be analytically calculated after adopting specific (e.g.. exponential
and Gaussian) shape for ρ(x). These general results are subsequently used to investigate flow toward a partially-penetrating well in a semi-infinite
domain. Indeed, we construct a σ2-order approximation to the mean as well as variance of the head by replacing the well with a singular segment. It is shown
how the well-length combined with the medium heterogeneity affects the head distribution. We have introduced the concept of
equivalent conductivity
K
eq(r,z). The main result is the relationship where the characteristic function ψ(w)(r,z) adjusts the homogeneous conductivity K
A
to account for the impact of the heterogeneity. In this way, a procedure can be developed to identify the aquifer hydraulic
properties by means of field-scale head measurements. Finally, in the case of a fully penetrating well we have expressed the
equivalent conductivity in analytical form, and we have shown that (being the effective conductivity for mean uniform flow), in agreement with the numerical simulations of Firmani et al. (Water Resour
Res 42:W03422, 2006). 相似文献
6.
Qian Xinxin Zhao Yicong Santini Claire-Lise Pan Hongmiao Xiao Tian Chen Haitao Song Tao Li Jinhua Alberto Francois Brustlein Sophie Wu Long-Fei 《中国海洋湖沼学报》2021,39(6):2005-2014
Journal of Oceanology and Limnology - Magnetotactic bacteria (MTB) synthesize intracellular magnetic organelles, magnetosomes, which consist of magnetic crystals that are enveloped in a membrane.... 相似文献
7.
Modelling of field-scale transport of chemicals is of deep interest to public as well as private sectors, and it represents an area of active theoretical research in many environmentally-based disciplines. However, the experimental data needed to validate field-scale transport models are very limited due to the numerous logistic difficulties that one faces out. 相似文献
8.
For the first time, vertical fluxes of mineral dust measured by Eddy Covariance in two desert sites of Northern Asia have been used to test the performances of a wind erosion model in the field. Soil parameters required by the model were obtained through field and laboratory determinations. Model predictions and direct measurements have been compared. The main finding was that the direction of the horizontal wind relative to the orientation of nebkhas played a crucial role in determining the emission of particles in one of the investigated sites. Being unable to simulate such interaction, the model generally overestimated the actual emission. It provided, instead, reliable predictions (r2 = 0·87) when the wind direction was suitable in detaching loose erodible elements placed on nebkhas thanks to their normal orientation. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
9.
Catherine E. Lovelock Maria Fernanda Adame Vicki Bennion Matthew Hayes Julian O’Mara Ruth Reef Nadia S. Santini 《Estuaries and Coasts》2014,37(3):763-771
Mangrove forests and saltmarshes are important habitats for carbon (C) sequestration in the coastal zone but variation in rates of C sequestration and the factors controlling sequestration are poorly understood. We assessed C sequestration in Moreton Bay, South East Queensland in mangrove forests and tidal marshes that span a range of environmental settings and plant communities, including mangrove forests and tidal marshes on the oligotrophic sand islands of the eastern side of Moreton Bay and on the nutrient enriched, western side of the bay adjacent to the city of Brisbane. We found that rates of C sequestration in sediments were similar among mangrove forests over the bay, despite large differences in the C density of sediments, because of different rates of vertical accretion of sediments. The C sequestration on the oligotrophic sand island tidal marshes, dominated by Juncus kraussii, had the highest rate of C sequestration in the bay while the western saltmarshes, which were dominated by Sarcocornia quinqueflora, had the lowest rate of C sequestration. Our data indicate C sequestration varies among different tidal wetland plant community types, due to variation in sediment characteristics and rates of sediment accretion over time. 相似文献
10.
Monia Santini Salvatore Grimaldi Fernando Nardi Andrea Petroselli Maria Cristina Rulli 《Geomorphology》2009,113(1-2):110
Terrain analysis applications using remotely sensed Digital Elevation Models (DEMs), nowadays easily available, permit to quantify several river basin morphologic and hydrologic properties (e.g. slope, aspect, curvature, flow path lengths) and indirect hydrogeomorphic indices (e.g. specific upslope area, topographic wetness index) able to characterize the physical processes governing the landscape evolution (e.g. surface saturation, runoff, erosion, deposition). Such DEMs often contain artifacts and the automated hydrogeomorphic characterization of the watershed is influenced by terrain analysis procedures consisting in artificial depression (pit) and flat area treatment approaches combined with flow direction methods.In shallow landslide deterministic models, when applied using topographic dataset at medium scale (e.g. 30 m of resolution), the choice of the most suitable DEM-processing procedure is not trivial and can influence model results. This also affects the selection of most critical areas for further finer resolution studies or for the implementation of countermeasures aiming to landslide risk mitigation.In this paper such issue is investigated using as topographic input the ASTER DEMs and comparing two different combinations of DEM correction and flow routing schemes. The study areas comprise ten catchments in Italy for which hydrogeomorphic processes are significant. Aims of this paper are: 1) to introduce a parameter estimation procedure for the physically-based DEM correction method PEM4PIT (Physical Erosion Model for PIT removal); 2) to investigate the influence of different terrain analysis procedures on results of the slope stability model SHALSTAB (SHAllow Landsliding STABility) using remotely-sensed ASTER DEMs; 3) trying to assess which of terrain analysis methods is more appropriate for describing terrain instability. 相似文献