Models under location uncertainty are derived assuming that a component of the velocity is uncorrelated in time. The material derivative is accordingly modified to include an advection correction, inhomogeneous and anisotropic diffusion terms and a multiplicative noise contribution. This change can be consistently applied to all fluid dynamics evolution laws. This paper continues to explore benefits of this framework and consequences of specific scaling assumptions. Starting from a Boussinesq model under location uncertainty, a model is developed to describe a mesoscale flow subject to a strong underlying submesoscale activity. Specifically, turbulent diffusion and rotation effects have similar orders of magnitude. As obtained, the geostrophic balance is modified and the Quasi-Geostrophic assumptions remarkably lead to a zero Potential Vorticity. The ensuing Surface Quasi-Geostrophic model provides a simple diagnosis of warm frontolysis and cold frontogenesis. 相似文献
A method to build synthetic hydrographs is introduced, based on 1300 gauging stations in France and Switzerland, covering a wide range of size and climatology. For each station, an average of two floods per year are selected by a peak-over-threshold method, providing about 69?000 hydrographs. For a given catchment, some “donor stations” are selected with criteria of proximity in space, size and runoff production. These donors provide hundreds of hydrographs which can complement the ones recorded locally, or replace them if no hydrograph is available. With this subset of hydrographs, one can estimate the catchment’s average peak-to-volume ratio of floods, and build the corresponding median hydrograph. Another application is, for a given daily discharge sequence (being observed or simulated), to generate a relevant synthetic hydrograph by combining appropriate hydrographs of the subset. These methods are assessed by performing a jack-knife validation on a wide dataset of stations. 相似文献
This paper presents a Bayesian methodology for updating the seismic hazard curves. The methodology is based on the comparison of predictive exceedance rates of a fixed acceleration level (given by the seismic hazard curves) and the observed exceedance rates in some selected sites. The application of the methodology needs, firstly, the definition of a prior probabilistic seismic hazard assessment based in a logic tree. Each main branch corresponds to a probabilistic model of calculus of seismic hazard. The method considers that, initially (or a priori), the weights of all branches of the logic tree are equivalent. Secondly, the method needs to compile the observations in the region. They are introduced in a database containing the recorded acceleration data (during the instrumental period). Nevertheless, the instrumental period in stable zones (as France) shows only very low acceleration levels recorded during a short observation period. Then, a method to enlarge the REX (number of observations) is presented taking into account the historical data and defining “synthetic” accelerations in the sites of observation. The synthetic REX allows to expand the period of observation and to increase the acceleration thresholds used in the Bayesian updating process. The application of the Bayesian approach leads to a new and more objective definition of the weights of each branch of the logic tree and, therefore, to new seismic hazard curves (mean and centiles). The Bayesian approach doesn’t change the probabilistic models (seismic hazard curves). It only modifies the weights of each branch of the logic tree. 相似文献
We compare the performances of four stochastic optimisation methods using four analytic objective functions and two highly non‐linear geophysical optimisation problems: one‐dimensional elastic full‐waveform inversion and residual static computation. The four methods we consider, namely, adaptive simulated annealing, genetic algorithm, neighbourhood algorithm, and particle swarm optimisation, are frequently employed for solving geophysical inverse problems. Because geophysical optimisations typically involve many unknown model parameters, we are particularly interested in comparing the performances of these stochastic methods as the number of unknown parameters increases. The four analytic functions we choose simulate common types of objective functions encountered in solving geophysical optimisations: a convex function, two multi‐minima functions that differ in the distribution of minima, and a nearly flat function. Similar to the analytic tests, the two seismic optimisation problems we analyse are characterised by very different objective functions. The first problem is a one‐dimensional elastic full‐waveform inversion, which is strongly ill‐conditioned and exhibits a nearly flat objective function, with a valley of minima extended along the density direction. The second problem is the residual static computation, which is characterised by a multi‐minima objective function produced by the so‐called cycle‐skipping phenomenon. According to the tests on the analytic functions and on the seismic data, genetic algorithm generally displays the best scaling with the number of parameters. It encounters problems only in the case of irregular distribution of minima, that is, when the global minimum is at the border of the search space and a number of important local minima are distant from the global minimum. The adaptive simulated annealing method is often the best‐performing method for low‐dimensional model spaces, but its performance worsens as the number of unknowns increases. The particle swarm optimisation is effective in finding the global minimum in the case of low‐dimensional model spaces with few local minima or in the case of a narrow flat valley. Finally, the neighbourhood algorithm method is competitive with the other methods only for low‐dimensional model spaces; its performance sensibly worsens in the case of multi‐minima objective functions. 相似文献
Natural Resources Research - The ~?115,000 km2 Volta Basin of Ghana is one of the most studied geological terrains. However, unlike the Birimian and Tarkwaian which have been... 相似文献
AbstractThere has been the call to forge a synergistic relationship between local ecological knowledge and formal institutions in the governance of natural resources. How do informal institutions complement the efforts of formal state regulation of natural resources? How does this complementation foster a regularized human–wildlife interaction? Adopting an ethnographic design, this study assesses the role of institutional complementation in natural resource governance using the case of Boabeng–Fiema Monkey Sanctuary (BFMS) in Ghana, West Africa. We purposively selected 33 informants relevant to the BFMS governance process. The study observes that the synergy between formal and informal institutions strengthens wildlife protection in BFMS and the surrounding villages. The usefulness of informal rules is enhanced if appropriately complemented with a formal institutional arrangement. Over time, it becomes necessary for informal rules to grow in dynamism to depict the principles of collaboration, inclusivity, and benefit arrangements. 相似文献
In this study, deposit- and district-scale three-dimensional (3D) fault-and-intrusion structure models were constructed, based on which a numerical simulation was implemented in the Jiaojia gold district, China. The numerical simulation of the models shows the basic metallogenic path and trap of the gold deposits using mineral system theory. The objective of this study was to delineate the uncertainty of the geometry or buffer zones of the ore-forming and ore-controlling fault-and-intrusion domains in 3D environment representing the exploration criteria extraction and the gold potential targeting in the study area. The fast Lagrangian analysis of continua in three dimensions was used as the platform to define the stress deformation fracture ore storage and the hydrothermal seepage channel zone based on the gold deposit features and metallogenic model in the study area. The validity of the numerical simulation was verified by comparing it with robust 3D geological models of the large Xincheng gold deposit. The potential targeting zones are analyzed for uncertainty and then evaluated by Boolean operation in a 3D geological model using the computer-aided design platform. The research results are summarized as follows. (1) In the pre-mineralization period, the Jiaodong fault’s left lateral movement created the Jiaojia network faults and formed a fracture zone with NW- to NNW-trending dips of 20° to 40°. (2) During the mineralization period, hydrothermal flow was associated with the intrusion geometry and features. However, it was constrained by the Jiaojia fault, which blocked the vadose flow into the upper wall rock and made the hydrothermal route close to the fault in the footwall fracture zones. (3) Three gold potential targets were identified by the numerical simulation results in the study area: the NW-trending Sizhuang gold deposit, the NW-trending zone of Jiaojia gold deposit, and the NE-trending zone of the Xincheng gold deposit. (4) The numerical simulation results show the fault-and-intrusion metallogenic domain and the hydrothermal alteration zones, which reflect the main ore-controlling and ore-forming factors of mineralization. The information obtained through the numerical simulation discussed here can be used to define exploration criteria in the study area.
The first erosional front of the south‐eastern Alps has been affected by several deep‐seated landslides. The movements affected a Jurassic limestone sequence underlain by an upper Trias unit (Keuper) mainly composed of marl and clays. Horst‐ and graben‐like structures, newly formed gravitational faults, outflow and other field evidence suggest that such movements are consistent with lateral rock spreading processes. An example of such processes is the ‘La Marbrière’ slope, where field investigations have revealed that three distinct zones corresponding to three evolutionary stages of movement exist. The question is: What are the structural and mechanical modifications undergone by the slope between those evolution stages? To tackle this question, numerical models based on a 2D cross section of the ‘La Marbrière’ slope have been performed. Results show that, to fit the structural evidence of the precollapse situation, elasto‐plastic behaviour of the Trias Keuper unit is needed. The transition between the precollapse and fresh post‐collapse situations requires a modification of the mechanical behaviour of the Trias Keuper unit to Burger type, resulting in the formation of antithetic and synthetic gravitational faults (producing a graben‐like structure). 相似文献