Inverse analysis of stochastic moment equations for transient flow in randomly heterogeneous media     

Monica Riva  Alberto Guadagnini  Shlomo P. Neuman  Emanuela Bianchi Janetti  Bwalya Malama 《Advances in water resources》2009

We present a nonlinear stochastic inverse algorithm that allows conditioning estimates of transient hydraulic heads, fluxes and their associated uncertainty on information about hydraulic conductivity (K) and hydraulic head (h  ) data collected in a randomly heterogeneous confined aquifer. Our algorithm is based on Laplace-transformed recursive finite-element approximations of exact nonlocal first and second conditional stochastic moment equations of transient flow. It makes it possible to estimate jointly spatial variations in natural log-conductivity (Y=lnK)$(Y=\ln K)$, the parameters of its underlying variogram, and the variance–covariance of these estimates. Log-conductivity is parameterized geostatistically based on measured values at discrete locations and unknown values at discrete “pilot points”. Whereas prior values of Y at pilot point are obtained by generalized kriging, posterior estimates at pilot points are obtained through a maximum likelihood fit of computed and measured transient heads. These posterior estimates are then projected onto the computational grid by kriging. Optionally, the maximum likelihood function may include a regularization term reflecting prior information about Y. The relative weight assigned to this term is evaluated separately from other model parameters to avoid bias and instability. We illustrate and explore our algorithm by means of a synthetic example involving a pumping well. We find that whereas Y and h can be reproduced quite well with parameters estimated on the basis of zero-order mean flow equations, all model quality criteria identify the second-order results as being superior to zero-order results. Identifying the weight of the regularization term and variogram parameters can be done with much lesser ambiguity based on second- than on zero-order results. A second-order model is required to compute predictive error variances of hydraulic head (and flux) a posteriori. Conditioning the inversion jointly on conductivity and hydraulic head data results in lesser predictive uncertainty than conditioning on conductivity or head data alone.  相似文献   

Petrology of lavas from the 2004–2005 flank eruption of Mt. Etna,Italy: inferences on the dynamics of magma in the shallow plumbing system     

Rosa Anna Corsaro  Lucia Civetta  Valeria Di Renzo  Lucia Miraglia 《Bulletin of Volcanology》2009,71(7):781-793

Following the 2001 and 2002–2003 flank eruptions, activity resumed at Mt. Etna on 7 September 2004 and lasted for about 6 months. This paper presents new petrographic, major and trace element, and Sr–Nd isotope data from sequential samples collected during the entire 2004–2005 eruption. The progressive change of lava composition allowed defining three phases that correspond to different processes controlling magma dynamics inside the central volcano conduits. The compositional variability of products erupted up to 24 September is well reproduced by a fractional crystallization model that involves magma already stored at shallow depth since the 2002–2003 eruption. The progressive mixing of this magma with a distinct new one rising within the central conduits is clearly revealed by the composition of the products erupted from 24 September to 15 October. After 15 October, the contribution from the new magma gradually becomes predominant, and the efficiency of the mixing process ensures the emission of homogeneous products up to the end of the eruption. Our results give insights into the complex conditions of magma storage and evolution in the shallow plumbing system of Mt. Etna during a flank eruption. Furthermore, they confirm that the 2004–2005 activity at Etna was triggered by regional movements of the eastern flank of the volcano. They caused the opening of a complex fracture zone extending ESE which drained a magma stored at shallow depth since the 2002–2003 eruption. This process favored the ascent of a different magma in the central conduits, which began to be erupted on 24 September without any significant change in eruptive style, deformation, and seismicity until the end of eruption.  相似文献   

SGeMS: A Free and Versatile Tool for Three-Dimensional Geostatistical Applications     

Marco Bianchi  Chunmiao Zheng 《Ground water》2009,47(1):8-12

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A seismic investigation into the geometry and controls upon alluvial architecture in the Walloon Subgroup,Surat Basin,Queensland     

D. Shields  V. Bianchi  J. Esterle 《Australian Journal of Earth Sciences》2017,64(4):455-469

The sedimentology of the Walloon Subgroup (WSG) has been extensively studied; however, gaps exist in our understanding of the succession's alluvial architecture and the mechanisms controlling its complex internal organisation. Successful coal-seam gas development in the Surat Basin requires the construction of predictive facies models, which in turn necessitates a fulsome understanding of the geometry and controls on the spatial and temporal distribution of alluvial sub-environments. To improve our models of WSG facies, this study employs an open-source high-resolution 3D seismic dataset available on the western limb of the Surat Basin. Integration of core, wireline and seismic data has resolved the geometries of four discrete alluvial architectural elements, representing simple channel, channel belt, crevasse splay complexes and peat-mire sub-environments. Channel belts were found to be 1600–2000 m wide, simple channels 400–800 m in width and crevasse splays averaging 3.5 × 5.5 km. Coal bodies mapped from seismic attribute extractions were found to be 4.2 km² on average. The high-resolution dataset has also yielded insight into the geological controls governing the spatial and temporal distribution of these sub-environments, explaining, in part the mechanisms responsible for the complex internal distribution of facies within the WSG. In places within the study area, the WSG's sedimentary organisation appears to be initiated by the rejuvenation of deep-seated tectonic features, the expression of which is propagated upward via the mechanics of compensational stacking.  相似文献   

A New Seismic Data Set on the Depth of the Moho in the Alps     

Irene Bianchi  Michael Behm  Eva Maria Rumpfhuber  Götz Bokelmann 《Pure and Applied Geophysics》2015,172(2):295-308

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Radionuclide Transport Behavior in a Generic Geological Radioactive Waste Repository          下载免费PDF全文

Marco Bianchi  Hui‐Hai Liu  Jens T. Birkholzer 《Ground water》2015,53(3):440-451

We performed numerical simulations of groundwater flow and radionuclide transport to study the influence of several factors, including the ambient hydraulic gradient, groundwater pressure anomalies, and the properties of the excavation damaged zone (EDZ), on the prevailing transport mechanism (i.e., advection or molecular diffusion) in a generic nuclear waste repository within a clay‐rich geological formation. By comparing simulation results, we show that the EDZ plays a major role as a preferential flowpath for radionuclide transport. When the EDZ is not taken into account, transport is dominated by molecular diffusion in almost the totality of the simulated domain, and transport velocity is about 40% slower. Modeling results also show that a reduction in hydraulic gradient leads to a greater predominance of diffusive transport, slowing down radionuclide transport by about 30% with respect to a scenario assuming a unit gradient. In addition, inward flow caused by negative pressure anomalies in the clay‐rich formation further reduces transport velocity, enhancing the ability of the geological barrier to contain the radioactive waste. On the other hand, local high gradients associated with positive pressure anomalies can speed up radionuclide transport with respect to steady‐state flow systems having the same regional hydraulic gradients. Transport behavior was also found to be sensitive to both geometrical and hydrogeological parameters of the EDZ. Results from this work can provide useful knowledge toward correctly assessing the post‐closure safety of a geological disposal system.  相似文献   

BACI design reveals the decline of the seagrass Posidonia oceanica induced by anchoring     

Montefalcone M  Chiantore M  Lanzone A  Morri C  Albertelli G  Nike Bianchi C 《Marine pollution bulletin》2008,56(9):1637-1645

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Microbial food web contributions to bottom water hypoxia in the northern Gulf of Mexico     

Michael Dagg  Riki Sato  Hongbin Liu  Thomas S. Bianchi  Rebecca Green  Rodney Powell 《Continental Shelf Research》2008

Nutrients from the Mississippi/Atchafalaya Rivers greatly stimulate biological production in the ‘classical’ food web on the inner shelf of the northern Gulf of Mexico. Portions of this production, especially large diatoms and zooplankton fecal pellets, sink and decompose in the bottom water, consuming oxygen and contributing to the annual development of an extensive zone of bottom water hypoxia, typically >15,000 km² since 1993. The microbial food web is also active in the Mississippi River plume, but consists of small organisms that sink slowly. This ‘recycling’ food web has not been considered as a significant contributor to vertical flux and hypoxia. However, gelatinous zooplankton, especially pelagic appendicularians such as Oikopleura dioica, mediate the conversion of microbial web organisms to organic particles with high sinking rates. When pelagic appendicularians are abundant in coastal regions of the northern Gulf of Mexico, they stimulate the rapid vertical transfer of microbial web productivity in the surface layer, which is only 5–15 m thick in the coastal hypoxic region, to the sub-pycnocline layer that becomes hypoxic each summer. In this paper we present results from two studies examining the significance of this pathway. In both 2002 and 2004, we observed high production rates of appendicularians in coastal waters. Discarded gelatinous houses and fecal pellets from the appendicularian populations often provided more than 1 g m⁻² d⁻¹ of organic carbon for the establishment and maintenance of hypoxia in the northern Gulf of Mexico. This source of organic matter flux is especially important in regions far from the river plumes and during periods of low river discharge. Autotrophic elements of this food web are primarily supported by recycled inorganic nutrients originating in the Mississippi and Atchafalaya Rivers. Sources of dissolved organic matter (DOM) supporting the heterotrophic components of this microbial food web may include in situ production, the Mississippi/Atchafalaya Rivers, and Louisiana's coastal wetlands. If significant, the latter source provides a possible link between Louisiana's high rates of coastal land loss and the large hypoxic zone observed along the coast during summer. Both of the latter DOM sources are independent of phytoplankton production stimulated by inputs of riverine inorganic nutrients.  相似文献   

The imprint of the equation of state on the axial w-modes of oscillating neutron stars     

Omar Benhar  Emanuele Berti  Valeria Ferrari 《Monthly notices of the Royal Astronomical Society》1999,310(3):797-803

We discuss the dependence of the pulsation frequencies of the axial quasi-normal modes of a non-rotating neutron star upon the equation of state describing the star interior. The continued fraction method has been used to compute the complex frequencies for a set of equations of state based on different physical assumptions and spanning a wide range of stiffness. The numerical results show that axial gravitational waves carry relevant information on both the structure of neutron star matter and the nature of the hadronic interactions.  相似文献   

Probing crustal anisotropy by receiver functions at the deep continental drilling site KTB in Southern Germany     

Irene Bianchi  Götz Bokelmann 《Geophysical Prospecting》2019,67(9):2450-2464

Seismic anisotropy is a unique observational tool for remotely studying deformation and stress within the Earth. Effects of anisotropy can be seen in seismic data; they are due to mineral alignment, fractures or layering. Seismic anisotropy is linked to local stress and strain, allowing modern geophysics to derive geomechanical properties from seismic data for supporting well planning and fracking. For unravelling anisotropic properties of the crust, the teleseismic receiver functions methodology has started to be widely applied recently due to its ability in retrieving the three-dimensional characteristics of the media sampled by the waves. The applicability of this technique is tested here by a field test carried out around the Kontinental Tiefbohrung site in southeastern Germany. We compare our results to previous investigations of the metamorphic rock pile of the Zone Erbendorf-Vohenstrauss, drilled down to 9 km depth, which sampled an alternating sequence of paragneiss and amphibolite, in which a strong foliation has been produced by ductile deformation. The application of the receiver functions reveals the presence of two distinct anisotropic layers within the metamorphic rock pile at 0–4 km and below 6 km depth, with up to 8% anisotropy; the depth of these two layers corresponds to the location of mica-rich paragneiss which show intense foliation, and finally proves the relation between the signal in the receiver functions, rock texture and presence of cracks. We have now the capability of providing insights from passive seismic data on geomechanical properties of the rocks, useful for geological exploration and engineering purposes, which will help influencing expensive drilling decisions thanks to future application of this seismic technique.  相似文献