Notices

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  • Publication
    Métadonnées seulement
    A deterministic approach to the coupled analysis of karst springs' hydrographs and chemographs
    (2003)
    Grasso, D Alessandro
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    Jeannin, Pierre-Yves 
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    Zwahlen, François 
    During the chemically based recession flow phase of karstic springs the carbonate (dissolved limestone) concentration can be expressed as negative power of the flow rate. The empirically determined Conc/Q relationship allows two parameters (alpha and A) to be defined, of which one (alpha) depends on the geometric dimensions of the saturated (submerged) karstic network. In this paper we present a deterministic model which simulates the concentration of carbonate at the outlet of a network of circular rectilinear conduits as a function of flow rate. This model, based on hydraulic principles and the calcite dissolution kinetics, allows the sensitivity of the alpha and A parameters to be studied under different chemical, physical and geometric scenarios. Simulation results show that A is a function of the calcite saturation concentration, whereas alpha depends on the spatial dimensions of the karstic network (void length and aperture). The deterministic model results were applied to real karstic systems to evaluate the geometric dimensions of submerged karstic networks. (C) 2002 Elsevier Science B.V. All rights reserved.
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    Métadonnées seulement
    A fast algorithm for the estimation of the equivalent hydraulic conductivity of heterogeneous media
    (2000-1-10)
    Renard, Philippe 
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    Le Loc'h, Gaëlle
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    Ledoux, Emmanuel
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    De Marsily, Ghislain
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    Mackay, Rae
  • Publication
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    A fluid-pressure feedback model of dehydration reactions: experiments, modelling, and application to subduction zones
    (2003)
    Miller, Stephen Andrew 
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    van der Zee, Wouter
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    Olgaard, David L.
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    Connolly, James A. D.
    Dehydration and melting reactions generate large volumes of fluid in the crust and upper mantle, and play an important role in subduction zone seismicity. The fluid pathway must evolve from isolated pockets in low porosity, low permeability rock, coalescing to interconnected permeable pathways to the surface. When fluid pressures generated from a dehydration or melting reaction are sufficient to induce hydrofracture, then hydrofracture significantly influences the porosity-permeability structure within the dehydrating/melting horizon. If a low fluid-pressure boundary is introduced to the dehydrating rock, then fluid will be driven from the rock along the evolved permeable network toward that boundary. The resulting pressure reduction can then accelerate the dehydration reaction and further drive the flow. The sudden introduction of a low fluid-pressure boundary may occur by the co-seismic (dilatant) rupturing of a pressure seal that connects different fluid pressure states. This mechanism is invoked to explain the observed post-seismic evolution of wave velocities (V-p/V-s,) following the 1995 Antofagasta, Chile earthquake. We show experimental results and introduce a conceptual and numerical model that reflects this scenario. The model couples the mechanical and thermodynamic effects of fluid pressure with devolitization kinetics, and is quantitatively consistent with experimental studies of the dehydration of gypsum and serpentine. The experimental results show that dehydration is controlled by access to a free (drained) boundary. The model provides a mechanistic explanation for the experimental observations and has applications in understanding the role of transient transport networks on the large-scale behavior of dehydrating and melting systems. (C) 2003 Elsevier B.V. All rights reserved.
  • Publication
    Métadonnées seulement
    A forward model for earthquake generation on interacting faults including tectonics, fluids, and stress transfer
    (2001)
    Fitzenz, Delphine D.
    ;
    Miller, Stephen Andrew 
    We present a forward model of interacting faults for systems of any geometry. The model generalizes that of Miller et al. [1996,1999] to a fully three-dimensional model where faults of any strike and geometry interact through an elastic matrix using the general solutions of Okada [1992]. The model includes large-scale plate motion loading and increasing pore pressures from a source term, undrained poroelastic effects, large coseismic hydraulic property changes, and porosity creation through dilatant slip. To illustrate the basic behavior and utility of the model, results are presented of the long-term evolution (approximate to 9300 years) for a generic case of a blind, dipping fault and a subvertical strike-slip fault in a transpressional environment. We show the stress state evolution along both faults, seismicity time lines, quasi-static rupture propagation including rake angle changes, local and regional stress buildup and rotations, static and dynamic fault interactions, and Delta CFS (changes in Coulomb Failure Stress) within the fault system. Large compartments of varying overpressure result on both faults from coseismic pore pressure changes and contribute to the complexity of the stress state. For the considered case, we find that the poroelastic effects on the receiver fault are about twice the change in the shear stress, providing a significant contribution to the Delta CFS. Regional stress rotations in response to the model seismicity indicate that further model developments must include dynamic generation of new faults in response to the evolving tectonic regime.
  • Publication
    Métadonnées seulement
    A model of deep crustal fluid flow following the M-w=8.0 Antofagasta, Chile, earthquake
    (2004)
    Koerner, A.
    ;
    Kissling, E.
    ;
    Miller, Stephen Andrew 
    We develop a model to test the hypothesis that a high fluid pressure pulse and subsequent fluid flow caused a spatially extensive increase in the V-P/V-S ratio following the M-w = 8.0 Antofagasta, Chile, subduction zone earthquake. The postseismic anomaly appeared within a 50-day period inside the forearc region of the Andes continental crust. We model this anomaly with a poroelastic medium that combines the fluid flow response to mean stress changes from slip along a dislocation plane, with a pore pressure pulse initiated by the coseismic rupturing of a seal separating hydrostatic-lithostatic fluid pressure conditions in the hanging walls and footwalls of the subduction zone, respectively. Variations in seismic velocity due to porosity and pore pressure changes are calculated using Gassmann's formula and the empirical law of critical porosity. We show that the slip-induced perturbation of the mean stress field is insufficient to explain the anomaly, but the release of lithostatic pressurized fluid trapped below the rupture plane ( within the oceanic crust) can explain the transient changes in seismic velocities. Our preferred model requires a very large intrinsic permeability of around 1 x 10(-1)3 m(2), suggesting a mechanism of a high-amplitude pressure pulse propagating through a highly permeable fracture system of the lower continental crust.
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  • Publication
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    A Perspective on the numerical-Solution of Convection-dominated Transport Problems - a Price to Pay for the Easy Way Out
    (1992)
    Noorishad, J
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    Tsang, C F
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    Perrochet, Pierre 
    ;
    Musy, André
    In a brief but fundamental review of the evolution of the conventional numerical techniques used in the solution of convection-dominated transport problems, we explore the difficulties that have been remedied to various degrees by various workers. In the course of this review we obtain the performance characteristic of the Crank-Nicolson Galerkin finite element method in the form of a curve in Peclet number and Courant number space. We show that the performance can be altered through a new upwind parameter that can easily be incorporated into many of the existing numerical solution methods. By providing an insight into the limitations of some of these methods we demonstrate, by means of numerical experiments, that the proposed upwinding procedure ensures acceptable solutions throughout the Pe-Cr space at a reasonable cost of the smearing effect.
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  • Publication
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    A relative-least-squares technique to determine unique Monod kinetic parameters of BTEX compounds using batch experiments
    (1999)
    Schirmer, Mario 
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    Butler, Barbara J
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    Roy, James W
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    Frind, Emil O
    ;
    Barker, James F
    An analysis of aerobic m-xylene biodegradation kinetics was performed on the results of laboratory batch microcosms. A modified version of the computer model BIO3D was used to determine the Monod kinetic parameters, k(max) (maximum utilization rate) and K-S (half-utilization constant), as well as the Haldane inhibition concentration, K-I, for pristine Borden aquifer material, The proposed method allows for substrate degradation under microbial growth conditions. The problem of non-uniqueness of the calculated parameters was overcome by using several different initial substrate concentrations. With a relative-least-squares technique, unique kinetic degradation parameters were obtained. Calculation of the microbial yield, Y, based on microbial counts from the beginning and the end of the experiments was crucial for reducing the number of unknowns in the system and therefore for the accurate determination of the kinetic degradation parameters, The kinetic parameters obtained in the present study were found to agree well with values reported in the literature. (C) 1999 Elsevier Science B.V. All rights reserved.
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  • Publication
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    A Streamline-Upwind-Full-Galerkin Method for Space-Time Convection Dominated Transport Problems
    (1993)
    Perrochet, Pierre 
    An original space-time finite element approach for the solution of the diffusion-convection equation is proposed in this paper. A slight manipulation of the differential equation suggests that transient transport problems may in fact be seen as 'steady-state space-time transport problems', accurately and easily soluble by the standard Galerkin technique. However, concerning convective transport involving sharp fronts or coarse discretization, it is shown that implementation of dissipation along space-time trajectories significantly improves the solutions. Classical comparative test problems are run to establish the performances of this method, and to show the limits of the more sophisticated Petrov and Taylor-Galerkin schemes. Evocation of a possible space-time anisotropy generated by usual finite difference time-stepping procedures, as well as comparative analysis of amplification matrices, help to understand the accuracy and the robustness of the proposed approach.
  • Publication
    Métadonnées seulement
    A three-dimensional fluid-controlled earthquake model: Behavior and implications
    (1999)
    Miller, Stephen Andrew 
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    Ben-Zion, Yehuda
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    Burg, Jean-Pierre
    We describe the behavior of a three-dimensional, fluid-controlled fault model that couples the dominant mechanical effects of fluid within a cellular fault zone with shear stress accumulation from constant plate motion applied at the downward continuation of the fault. Improvements from a previous model include long-term plate motion loading and porosity creation through dilatant slip, which allow the model to evolve to its steady state dynamic equilibrium. The examined results include slip and slip-deficit accumulation, pore pressure buildup and release, stress states, the emergence of seismic scaling relationships, and frequency-size statistics of model earthquakes. We find that asperities develop naturally within the model, reflecting the disorganization of the evolving stress state in Mohr space. The dynamical interaction of shear stress and effective normal stress perturbs the initial uniform stress state to a complex state that produces transient asperity development along the fault. These "Mohr-space" asperities spontaneously evolve, disintegrate, reemerge, and migrate along the fault plane. The general model behavior is independent of the state of the fluid pressure. In four examined cases, which span the range of possible fault zone overpressures, the equilibrium condition is that which occupies all of the available Mohr space. Maximum slip deficits along the fault depend on the degree of fault weakness, ranging from about 3 m for a weak fault to over 30 m for a strong fault after 4000 years of model evolution. For events that breach the surface the seismic moment scales with the cube of the source dimension M-o similar to L-3, which reflects the slipped area times the depth extent of the rupture. This scaling crosses isolines of stress drop. For confined events, M-o similar to L-2 along isolines of stress drop, but no general scaling emerges. Clusters emerge between stress drop versus seismic moment and stress drop versus source dimension, with large events converging to average stress drops of about 8 MPa for a weak fault and about 20 MPa for a strong fault.
  • Publication
    Métadonnées seulement
    Addressing conditioning data in multiple-point statistics simulation algorithms based on a multiple grid approach
    (2014-2)
    Straubhaar, Julien 
    ;
    Malinverni, Duccio
    Multiple-point statistics (MPS) allows simulations reproducing structures of a conceptual model given by a training image (TI) to be generated within a stochastic framework. In classical implementations, fixed search templates are used to retrieve the patterns from the TI. A multiple grid approach allows the large-scale structures present in the TI to be captured, while keeping the search template small. The technique consists in decomposing the simulation grid into several grid levels: One grid level is composed of each second node of the grid level one rank finer. Then each grid level is successively simulated by using the corresponding rescaled search template from the coarse level to the fine level (the simulation grid itself). For a conditional simulation, a basic method (as in snesim) to honor the hard data consists in assigning the data to the closest nodes of the current grid level before simulating it. In this paper, another method (implemented in impala) that consists in assigning the hard data to the closest nodes of the simulation grid (fine level), and then in spreading them up to the coarse grid by using simulations based on the MPS inferred from the TI is presented in detail. We study the effect of conditioning and show that the first method leads to systematic biases depending on the location of the conditioning data relative to the grid levels, whereas the second method allows for properly dealing with conditional simulations and a multiple grid approach.
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    Aluminous granulites from the Pulur complex, NE Turkey : a case of partial melting, efficient melt extraction and crystallisation
    (2004)
    Topuz, Gültekin
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    Altherr, Rainer
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    Kalt, Angelika 
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    Satır, Muharrem
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    Werner, Olaf
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    Schwarz, Winfried H.
    In the Pulur complex, NE Turkey, a heterogeneous rock sequence ranging from quartz-rich mesocratic gneisses to silica- and alkali-deficient, Fe-, Mg- and Al-rich melanocratic rocks is characterized by granulite-facies assemblages involving garnet, cordierite, sillimanite, ilmenite, ±spinel, ±plagioclase, ±quartz, ±biotite, ±corundum, rutile and monazite. Textural evidence for partial melting in the aluminous granulites, particularly leucosomes, is largely absent or strongly obliterated by a late-stage hydrothermal overprint. However, inclusion relations, high peak P–T conditions, the refractory modes, bulk and biotite compositions of the melanocratic rocks strongly support a model of partial melting. The melt was almost completely removed from the melanocratic rocks and crystallised within the adjacent mesocratic gneisses which are silica-rich, bear evidence of former feldspar and show a large range in major element concentrations as well as a negative correlation of most elements with SiO2. Peak conditions are estimated to be ≥800 °C and 0.7–0.8 GPa. Subsequent near-isothermal decompression to ~0.4–0.5 GPa at 800–730 °C is suggested by the formation of cordierite coronas and cordierite–spinel symplectites around garnet and in the matrix. Sm–Nd, Rb–Sr and 40Ar/39Ar isotope data indicate peak conditions at ~330 Ma and cooling below 300 °C at ~310 Ma.
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    An assessment of the groundwater resources in the western margin of the Taoudenni basin, Mauritania
    (: IAH Selected papers on Hydrogeology, 2007)
    Bertone, François
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    Renard, Philippe 
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    Kerrou, Jaouhar 
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    Moix, P.
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    Perrochet, P
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    Chery, L.
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    de Marsily, G.
  • Publication
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    Anaerobic degradation of vinyl chloride in aquifer microcosms
    (2011)
    Smits, T. H. M.
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    Assal, A.
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    Hunkeler, Daniel 
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    Holliger, C.
  • Publication
    Métadonnées seulement