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1.
In the early eighties Rundle (1980, 1981a,b, 1982) developed the techniques needed for calculations of displacements and gravity changes due to internal
sources of strain in layered linear elastic-gravitational media. The approximation of the solution for the half space was
obtained by using the propagator matrix technique. The Earth model considered is elastic-gravitational, composed of several
homogeneous layers overlying a bottom half space. Two dislocation sources can be considered, representing magma intrusions
and faults. In recent decades theoretical and computational extensions of that model have been developed by Rundle and co-workers
(e.g., Fernández and Rundle, 1994a,b; Fernández
et al., 1997, 2005a; Tiampo
et al., 2004; Charco
et al., 2006, 2007a,b). The source can be located at any depth in the media. In this work we prove that the perturbed equations
representing the elastic-gravitational deformation problem, with the natural boundary and transmission conditions, leads to
a well-posed problem even for varied domains and general data. We present constructive proof of the existence and we show
the uniqueness and the continuous dependence with respect to the data of weak solutions of the coupled elastic-gravitational
field equations. 相似文献
2.
Fco. Javier Pavón–Carrasco Maria Luisa Osete J. Miquel Torta Luis R. Gaya–Piqué 《Pure and Applied Geophysics》2008,165(6):1209-1225
The SCHA.DI.00 directional model for the geomagnetic field in Europe for the last 2000 years (Pavón–Carrasco
et al., 2008) has been updated by modelling the palaeointensity. This model, SCHA.DI.00, was developed from available Bayesian
European Palaeosecular Variation Curves using the regional Spherical Cap Harmonic Analysis technique. The comparison of the
palaeosecular variation curves, given by the regional model, with available archaeomagnetic data not used in its development
showed an improvement with respect to the fit obtained by global archaeomagnetic models. In this paper advantage is taken
of recently published palaeointensity databases to develop a complete (direction and intensity) regional archaeomagnetic model
for the last 2000 years valid for the European region: the SCHA.DI.00–F model. Not only does this complete model provide an
improvement for example for archaeomagnetic data studies, but it is also shown that this new regional model can be used to
study the recently proposed link between the centennial secular variation of the geomagnetic field and climate change. The
pattern of the archaeosecular variation of the field intensity obtained by SCHA.DI.00–F seems to verify the hypothesis presented
by Gallet et al. (2005) about a possible (causal) connection between changes in the geomagnetic field intensity and in climate parameters,
opening the door for more discussions on this challenging subject. 相似文献
3.
Chen Po-fang 《地震学报(英文版)》2002,15(5):519-525
To improve the accuracy of the numerical evaluation through the 3-D finite difference method, the surface boundary conditions
are added to modify the old program. The author has tested the new program by making calculations for the model constructed
by Wanamaker, et al (1984). The comparison between the numerical results obtained from this paper and those by Wannamaker, et al (1984) indicates that a pronounced improvement is realized in the evaluation of the horizontal magnetic components. Moreover,
better calculations for the vertical magnetic components are also obtainable by using the new program. 相似文献
4.
The CO2 and H2S concentration in the Solfatara atmosphere has been measured. The concentrations of both gases are higher neraby the more active areas and decrease away from them. A sharp horizontal and vertical gradient of the CO2 content has been recognized.Such gradient is assumed to result from a diffusion of gas from the ground to the atmosphere.The total output of CO2 has been computed based on a turbulent diffusion model. The obtained value is in good agreement with previously abserved values (Italiano
et al., 1984).The feasibility of monitoring the atmosphere of Solfatara for either gas hazard and surveillance of volcanic activity has also been evaluated. 相似文献
5.
O'Leary González Leonardo Alvarez Mariangela Guidarelli Giuliano F. Panza 《Pure and Applied Geophysics》2007,164(10):1985-2007
An overview of the crust and upper mantle structure of Central America and the Caribbean region is presented as a result of
the processing of more than 200 seismograms recorded by digital broadband stations from SSSN and GSN seismic networks. Group
velocity dispersion curves are obtained in the period range from 10s to 40s by FTAN analysis of the fundamental mode of the
Rayleigh waves; the error of these measurements varies from 0.06 and 0.09 km/s. From the dispersion curve, seven tomographic
maps at different periods and with average spatial resolution of 500 km are obtained. Using the logical combinatorial classification
techniques, eight main groups of dispersion curves are determined from the tomographic maps and eleven main regions, each
one characterized by one kind of dispersion curves, are identified. The average dispersion curves obtained for each region
are extended to 150s by adding data from a larger-scale tomographic study (Vdovin et al., 1999) and inverted using a nonlinear procedure. A set of models of the S-wave velocity vs. depth in the crust and upper
mantle is found as a result of the inversion process. In six regions we identify a typically oceanic crust and upper mantle
structure, while in the other two the models are consistent with the presence of a continental structure. Two regions, located
over the major geological zones of the accretionary crust of the Caribbean region, are characterized by a peculiar crust and
upper mantle structure, indicating the presence of lithospheric roots reaching, at least, about 200 km of depth. 相似文献
6.
A Godunov-Type Scheme for Atmospheric Flows on Unstructured Grids: Euler and Navier-Stokes Equations
Nash'at Ahmad Zafer Boybeyi Rainald Löhner Ananthakrishna Sarma 《Pure and Applied Geophysics》2007,164(1):217-244
In recent years there has been a growing interest in using Godunov-type methods for atmospheric flow problems. Godunov's unique
approach to numerical modeling of fluid flow is characterized by introducing physical reasoning in the development of the
numerical scheme (van Leer, 1999). The construction of the scheme itself is based upon the physical phenomenon described by the equation sets. These
finite volume discretizations are conservative and have the ability to resolve regions of steep gradients accurately, thus
avoiding dispersion errors in the solution. Positivity of scalars (an important factor when considering the transport of microphysical
quantities) is also guaranteed by applying the total variation diminishing condition appropriately. This paper describes the implementation of a Godunov-type finite volume scheme based on unstructured
adaptive grids for simulating flows on the meso-, micro- and urban-scales. The Harten-Lax-van Leer-Contact (HLLC) approximate
Riemann solver used to calculate the Godunov fluxes is described in detail. The higher-order spatial accuracy is achieved
via gradient reconstruction techniques after van Leer and the total variation diminishing condition is enforced with the aid of slope-limiters. A multi-stage explicit Runge-Kutta time marching scheme is used for
maintaining higher-order accuracy in time. The scheme is conservative and exhibits minimal numerical dispersion and diffusion.
The subgrid scale diffusion in the model is parameterized via the Smagorinsky-Lilly turbulence closure. The scheme uses a non-staggered mesh arrangement of variables (all quantities are
cell-centered) and requires no explicit filtering for stability. A comparison with exact solutions shows that the scheme can
resolve the different types of wave structures admitted by the atmospheric flow equation set. A qualitative evaluation for
an idealized test case of convection in a neutral atmosphere is also presented. The scheme was able to simulate the onset
of Kelvin-Helmholtz type instability and shows promise in simulating atmospheric flows characterized by sharp gradients without
using explicit filtering for numerical stability. 相似文献
7.
A. L. Metnieks 《Pure and Applied Geophysics》1965,61(1):183-190
Summary The value of three different methods for deducing aerosol size distribution from diffusional decay measurements — the exhaustion method proposed byPollak andMetnieks, the method byFuchs
et al. and the method byNolan andScott — is investigated with numerical examples of known distributions and also by applying them to laboratory experiments. It was found that the exhaustion method and the method proposed byFuchs
et al. are satisfactory for deducing the mean particle size and that none of the three methods is quite satisfactory for deducing dispersion of the distributions with higher accuracy. 相似文献
8.
Soil vapour extraction (SVE) is a common remediation technique for cleaning up unsaturated soils contaminated by volatile organic compounds (VOCs). Analytical solutions, which result from simple mathematical models, can allow the fast approximation of the time‐dependent effluent concentration and the gaining of insight into the processes that take place during soil remediation. Deriving the analytical solutions to advection–dispersion equations that simultaneously take into account the mechanical dispersion and molecular diffusion is very difficult because of the variable dependence of governing equations' coefficients. In this study, we first present two simplified analytical solutions that only consider mechanical dispersion or molecular diffusion. The two developed analytical solutions are compared with the numerical solution that simultaneously considers both mechanical dispersion and molecular diffusion to examine the applicability of the two simplified analytical solutions and distinguishes the individual contribution of the mechanical dispersion and molecular diffusion to total VOCs transport in an SVE system. Results show that dispersion plays an important role during SVE decontamination and neither the diffusion‐dominated solution nor the dispersion‐dominated solution can agree well with the numerical solution when both mechanical dispersion and molecular diffusion have significant contributions to the total VOCs transport flux. A composite analytical solution that linearly couples the diffusion‐ and dispersion‐dominated analytical solutions, which is proposed herein to eliminate the discrepancy between the analytical solutions and the numerical solution. Results indicate that the proposed composite analytical solution agrees well with the numerical solution and is an effective tool for quickly and accurately evaluating the time‐dependent effluent concentration for parameters of the different ranges of interest in an SVE remedial system. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
9.
Summary In the present paperTaylor's analysis of the dispersion of a soluble matter in Newtonian flow through a circular tube is extended in the case of non-Newtonian flows of Eyring and Reiner-Philippoff model fluids. It has been shown here that the results for the Newtonian fluid can be deduced from the corresponding results of both the two types non-Newtonian flows. Few specific cases of both the two types of fluids have been studied. Aris modification ofTaylor's analysis is also applicable to non-Newtonian flows discussed here. The results may be useful in connection with the study of the dispersion of soluble salts in blood vessels. It may also be useful to physicians who wish to study molecular diffusion coefficients. 相似文献
10.
Jean‐Sébastien Dubé Jean‐Philippe Boudreault 《Ground Water Monitoring & Remediation》2011,31(4):77-81
The dissolution of gases, such as oxygen, in groundwater is a means to provide electron acceptors required for the biological degradation of organic contaminants in aquifers. The use of polymeric emitters for passive gas diffusion in groundwater significantly increases the efficiency of oxygen transfer to the groundwater compared to conventional sparging. A critical parameter for the design of polymeric emitters is the diffusion coefficient (D) of the polymer tubing used to construct the emitters. Wilson and Mackay (1995) proposed a mathematical model (WM model) for the analysis of laboratory passive diffusion experiments aimed at characterizing D. Their analytical solution is obtained in Laplace space and its inversion requires the use of a numerical approximation technique. This article proposes an alternative to the WM model by simplifying it as a dimensionless ordinary differential equation (ODE) which is solved using simple integration. The validity of the dimensionless solution is discussed and the latter plotted into charts to provide easy‐to‐use analytical tools applicable to gas or solute diffusion in groundwater. 相似文献
11.
This article examines the required spatial discretization perpendicular to the fracture-matrix interface (FMI) for numerical simulation of solute transport in discretely fractured porous media. The discrete-fracture, finite-element model HydroGeoSphere ( Therrien et al. 2005 ) and a discrete-fracture implementation of MT3DMS ( Zheng 1990 ) were used to model solute transport in a single fracture, and the results were compared to the analytical solution of Tang et al. (1981) . To match analytical results on the relatively short timescales simulated in this study, very fine grid spacing perpendicular to the FMI of the scale of the fracture aperture is necessary if advection and/or dispersion in the fracture is high compared to diffusion in the matrix. The requirement of such extremely fine spatial discretization has not been previously reported in the literature. In cases of high matrix diffusion, matching the analytical results is achieved with larger grid spacing at the FMI. Cases where matrix diffusion is lower can employ a larger grid multiplier moving away from the FMI. The very fine spatial discretization identified in this study for cases of low matrix diffusion may limit the applicability of numerical discrete-fracture models in such cases. 相似文献
12.
Chen Po-fang 《地震科学（英文版）》2002,15(5):519-525
To improve the accuracy of the numerical evaluation through the 3-D finite difference method, the surface boundary conditions are added to modify the old program. The author has tested the new program by making calculations for the model constructed by Wanamaker, et al (1984). The comparison between the numerical results obtained from this paper and those by Wannamaker, et al (1984) indicates that a pronounced improvement is realized in the evaluation of the horizontal magnetic components. Moreover, better calculations for the vertical magnetic components are also obtainable by using the new program. 相似文献
13.
The velocity field in a river flow cross‐sectional area can be determined by applying entropy as done in 1978 by Chiu, who developed a two‐dimensional model of flow velocity based on the knowledge of maximum velocity, umax, and the dimensionless entropic parameter, characteristic of the river site. This is appealing in the context of discharge monitoring, particularly for high floods, considering that umax occurs in the upper portion of flow area and can be easily sampled, unlike velocity in the lower portion of flow area. The simplified form of Chiu's entropy‐based velocity model, proposed in 2004 by Moramarco et al., has been found to be reasonably accurate for determining mean flow velocity along each vertical sampled in the flow area, but no uncertainty analysis has been reported for this simplified entropy‐based velocity model. This study, therefore, performed uncertainty analysis of the simplified model following a procedure proposed by Misirli et al. in 2003. The flow velocity measurements at the Rosciano River section along the Chiascio River, central Italy, carried out for a period spanning 20 years were used for this purpose. Results showed that the simplified entropy velocity model was able to provide satisfactory estimates of velocity profiles in the whole flow area and the 95% confidence bands for the computed estimated mean vertical velocity were quite representative of observed values. In addition, using these 95% confidence bands, it was possible to have an indication of the uncertainty in the determination of mean cross‐sectional flow velocity as well. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
14.
15.
Resume En juin et juillet 1983, pendant l'éruption, on a procédé à une campagne de mesures magnéto-telluriques sur l'Etna. Elle a consisté en l'exécution de six sondages lents et d'une cinquantaine de mesures audio-magnéto-telluriques (AMT).On discute l'interprétation tant géophysique que structurale des données recueillies en tenant compte des conditions particulières dans lesquelles l'opération s'est effectuée. La méthode AMT identifie très bien la fracture majeure liée à l'éruption qui se manifeste par un baisse très sensible de la résistivité apparente. Les sondages lents, pour leur part, mettent en évidence des formations conductrices qu'il est difficile d'accorder avec le schéma proposé parR. Schick
et al.L'observation d'une évolution dans le temps de certaines mesures en AMT est discutée ainsi que les conséquences qu'on pourrait en tirer quant à la surveillance directe ou indirecte de la situation du magma en profondeur.
Magneto-telluric measurements were carried out during the Etna eruption in June–July 1983. Six slow soundings and about 50 audiomagneto-telluric (AMT) measurements formed the survey programme.Geophysical and structural interpretations of data are given with taking into account the particular operational conditions. The major fracture associated with the eruption has been identified by the AMT method quite well in a very clear low of the apparent resistivity. On the other hand, slow soundings have shown conductive rock formations which it is difficult to fit theSchick et al.'s model.The time evolution of certain AMT measurements is discussed together with the possible implication for a direct or indirect surveillance of the magma situation in depth.相似文献
16.
Advances in sensor techniques, digital acquisition, communication and computing allowed establishment of the field of real-time
seismology (Kanamori et al., 1997) and the design of earthquake information systems that provide rapid information on ground motion and potential damage
in an area for which a ground motion estimation data base is available and where the inventory of buildings and infrastructure
and its vulnerability to shaking is known. We discuss a system for the Romanian capital of Bucharest, where an early warning
system with about 30 seconds lead time, shake maps and a sophisticated damage estimation tool for Bucharest have been developed
in the frame of the Collaborative Research Center on Strong Earthquakes (). 相似文献
17.
The advection–dispersion equation with spatially variable coefficients does not have an exact analytical solution and is therefore solved numerically. However, solutions obtained with several of the traditional finite difference or finite element techniques typically exhibit spurious oscillation or numerical dispersion when advection is dominant. The mixing cell and semi-analytical solution methods proposed in this study avoid such oscillation or numerical dispersion when advection dominates. Both the mixing cell and semi-analytical solution methods calculate the spatial step size by equating numerical dispersion to physical dispersion. Because of the spatial variability of the coefficients the spatial step size varies in space. When the time step size Δt→0, the mixing cell method reduces to the semi-analytical solution method. The results of application to two cases show that the mixing cell and semi-analytical solution methods are better than a finite difference method used in the study. © 1998 John Wiley & Sons, Ltd. 相似文献
18.
ABSTRACT Forward–backward solute dispersion with an intermediate point source in one-dimensional semi-infinite homogeneous porous media is studied in this paper. Solute transport under sorption conditions, first-order decay and zero-order production terms are included. The first type of boundary condition is taken as a constant point source at an intermediate point from where forward and backward solute dispersion is examined. The Laplace transform method is adopted to solve the governing equation analytically. All the analytical results are obtained in graphical form to investigate the forward–backward solute transport in porous media for various hydrological input data. The graphical nature of the analytical solution is compared with numerical data taken from existing literature and similar results are obtained. Also, numerical solution of the governing equation is obtained by the Crank-Nicolson finite difference scheme and validated with the analytical solution, which demonstrates good agreement between them. Accuracy of the solution is also observed by using RMSE. 相似文献
19.
—?The aim of our study consists of analyzing potentially non-double-couple seismic events recorded at regional distances. In order to define the nature of the seismic source, a moment tensor inversion is carried out as this method is general enough not to initially constrain the source mechanism. In this paper we present an application to a seismic event induced by a mine collapse which occurred near the town of Halle in Germany. Because of its induced nature, many parameters such as the location and geometry of this seismic source are known. This information allows us to test the influence of inadequate propagation modeling on the moment tensor obtained from the inversion. Green's functions have been computed with the reflectivity method in a flat layered medium, using the European model EurID (Du et? al., 1998; Dufumier et al., 1997). From the inversion of P-wave seismograms recorded by the German Regional Seismic Network will, we obtained a source time function which can be decomposed into two subevents. The first one has a large isotropic part and a deviatoric mechanism with near vertical nodal planes. No volume change is observed for the second subevent, but a deviatoric component opposite of the first one. The addition of S-waves does not change the results of the inversion which are stable. Surface waves were not used because of their poor dispersion curves. Based on the moment tensor obtained from these inversions, the physical process at the source is compatible with a large cavity collapse. 相似文献
20.
Jean -Luc Got Vadim Monteiller Jean Virieux Paul Okubo 《Pure and Applied Geophysics》2006,163(2-3):405-430
Seismic velocity parameters in limited, but heterogeneous volumes can be inferred using a double-difference tomographic algorithm,
but to obtain meaningful results accuracy must be maintained at every step of the computation. MONTEILLER et al. (2005) have devised a double-difference tomographic algorithm that takes full advantage of the accuracy of cross-spectral
time-delays of large correlated event sets. This algorithm performs an accurate computation of theoretical travel-time delays
in heterogeneous media and applies a suitable inversion scheme based on optimization theory. When applied to Kilauea Volcano,
in Hawaii, the double-difference tomography approach shows significant and coherent changes to the velocity model in the well-resolved
volumes beneath the Kilauea caldera and the upper east rift. In this paper, we first compare the results obtained using MONTEILLER
et al.'s algorithm with those obtained using the classic travel-time tomographic approach. Then, we evaluated the effect of using
data series of different accuracies, such as handpicked arrival-time differences (``picking differences'), on the results
produced by double-difference tomographic algorithms. We show that picking differences have a non-Gaussian probability density
function (pdf). Using a hyperbolic secant pdf instead of a Gaussian pdf allows improvement of the double-difference tomographic
result when using picking difference data. We completed our study by investigating the use of spatially discontinuous time-delay
data. 相似文献