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51.
52.
The performance of the Ensemble Kalman Filter method (EnKF) depends on the sample size compared to the dimension of the parameters
space. In real applications insufficient sampling may result in spurious correlations which reduce the accuracy of the filter
with a strong underestimation of the uncertainty. Covariance localization and inflation are common solutions to these problems.
The Ensemble Square Root Filters (ESRF) is also better to estimate uncertainty with respect to the EnKF. In this work we propose
a method that limits the consequences of sampling errors by means of a convenient generation of the initial ensemble. This
regeneration is based on a Stationary Orthogonal-Base Representation (SOBR) obtained via a singular value decomposition of
a stationary covariance matrix estimated from the ensemble. The technique is tested on a 2D single phase reservoir and compared
with the other common techniques. The evaluation is based on a reference solution obtained with a very large ensemble (one
million members) which remove the spurious correlations. The example gives evidence that the SOBR technique is a valid alternative
to reduce the effect of sampling error. In addition, when the SOBR method is applied in combination with the ESRF and inflation,
it gives the best performance in terms of uncertainty estimation and oil production forecast. 相似文献
53.
Slope instability induced by volcano-tectonics as an additional source of hazard in active volcanic areas: the case of Ischia island (Italy) 总被引:1,自引:0,他引:1
Marta Della Seta Enrica Marotta Giovanni Orsi Sandro de Vita Fabio Sansivero Paola Fredi 《Bulletin of Volcanology》2012,74(1):79-106
Ischia is an active volcanic island in the Gulf of Naples whose history has been dominated by a caldera-forming eruption (ca.
55 ka) and resurgence phenomena that have affected the caldera floor and generated a net uplift of about 900 m since 33 ka.
The results of new geomorphological, stratigraphical and textural investigations of the products of gravitational movements
triggered by volcano-tectonic events have been combined with the information arising from a reinterpretation of historical
chronicles on natural phenomena such as earthquakes, ground deformation, gravitational movements and volcanic eruptions. The
combined interpretation of all these data shows that gravitational movements, coeval to volcanic activity and uplift events
related to the long-lasting resurgence, have affected the highly fractured marginal portions of the most uplifted Mt. Epomeo
blocks. Such movements, mostly occurring since 3 ka, include debris avalanches; large debris flows (lahars); smaller mass
movements (rock falls, slumps, debris and rock slides, and small debris flows); and deep-seated gravitational slope deformation.
The occurrence of submarine deposits linked with subaerial deposits of the most voluminous mass movements clearly shows that
the debris avalanches impacted on the sea. The obtained results corroborate the hypothesis that the behaviour of the Ischia
volcano is based on an intimate interplay among magmatism, resurgence dynamics, fault generation, seismicity, slope oversteepening
and instability, and eruptions. They also highlight that volcano-tectonically triggered mass movements are a potentially hazardous
phenomena that have to be taken into account in any attempt to assess volcanic and related hazards at Ischia. Furthermore,
the largest mass movements could also flow into the sea, generating tsunami waves that could impact on the island’s coast
as well as on the neighbouring and densely inhabited coast of the Neapolitan area. 相似文献
54.
This article presents a method for the direct displacement-based design of steel moment resisting frames, with specific consideration of beam-to-column joint characteristics. The method can be used for steel frames having any type of beam-to-column joints, from rigid and full-strength to semi-rigid and partial-strength. The plastic rotation capacity of the joints is explicitly taken into account within the performance criteria for the design. To assess the accuracy of the method in controlling performance, case study structures were first designed and subsequently analysed using non-linear dynamic analysis with a set of real accelerograms. For all cases, the mean of peak inter-storey drift demands and the mean of peak plastic rotation demands on joints were controlled in accordance with the limits set during design. The results obtained demonstrate that the proposed method is appropriate for the performance-based seismic design of steel moment resisting frames with different joint typologies. 相似文献
55.
Gianluca Iezzi Zhenxian Liu Giancarlo Della Ventura 《Physics and Chemistry of Minerals》2009,36(6):343-354
The high-pressure behavior of three synthetic amphiboles crystallized with space group P21/m at room conditions in the system Li2O–Na2O–MgO–SiO2–H2O has been studied by in situ synchrotron infrared absorption spectroscopy. The amphiboles have compositions ANa B(Na
x
Li1 − x
Mg1) CMg5 Si8 O22(OH)2 with x = 0.6, 0.2 and 0.0, respectively. The high-P experiments up to 32 GPa were carried out on the U2A beamline at Brookhaven National Laboratory (NY, USA) using a diamond
anvil cell under non-hydrostatic or quasi-hydrostatic conditions. The two most intense absorption bands in the OH-stretching
infrared spectra can be assigned to two non-equivalent O–H dipoles in the P21/m structure, bonded to the same local environment M1M3Mg3–OH–ANa, and pointing toward two differently kinked tetrahedral rings. In all samples these bands progressively merge to give a
unique symmetrical absorption with increasing pressure, suggesting a change in symmetry from P21/m to C2/m. The pressure at which the transition occurs appears to be linearly correlated to the aggregate B-site dimension. The infrared
spectra collected for amphibole B(Na0.2Li0.8Mg1) in the frequency range 50 to 1,400 cm−1 also show a series of changes with increasing pressure. The data reported here support the inference of Iezzi et al. (Am
Miner 91:479–482, 2006a) regarding a new high-pressure amphibole polymorph. 相似文献
56.
Gas hydrates and active mud volcanism on the South Shetland continental margin, Antarctic Peninsula 总被引:1,自引:0,他引:1
During the Antarctic summer of 2003–2004, new geophysical data were acquired from aboard the R/V OGS Explora in the BSR-rich area discovered in 1996–1997 along the South Shetland continental margin off the Antarctic Peninsula. The
objective of the research program, supported by the Italian National Antarctic Program (PNRA), was to verify the existence
of a potential gas hydrate reservoir and to reconstruct the tectonic setting of the margin, which probably controls the extent
and character of the diffused and discontinuous bottom simulating reflections. The new dataset, i.e. multibeam bathymetry,
seismic profiles (airgun and chirp), and two gravity cores analysed by computer-aided tomography as well as for gas composition
and content, clearly shows active mud volcanism sustained by hydrocarbon venting in the region: several vents, located mainly
close to mud volcanoes, were imaged during the cruise and their occurrence identified in the sediment samples. Mud volcanoes,
vents and recent slides border the gas hydrate reservoir discovered in 1996–1997. The cores are composed of stiff silty mud.
In core GC01, collected in the proximity of a mud volcano ridge, the following gases were identified (maximum contents in
brackets): methane (46 μg/kg), pentane (45), ethane (35), propane (34), hexane (29) and butane (28). In core GC02, collected
on the flank of the Vualt mud volcano, the corresponding data are methane (0 μg/kg), pentane (45), ethane (22), propane (0),
hexane (27) and butane (25). 相似文献
57.
58.
59.
F. Bella P. F. Biagi M. Caputo E. Cozzi G. Della Monica A. Ermini W. Plastino V. Sgrigna 《Pure and Applied Geophysics》1998,153(1):179-194
—The Gran Sasso chain (Central Apennines, Italy) contains one of the largest aquifers of Central Italy. From 1970–1986 the massif was tunnelled through in order to build up a highway and an international underground laboratory for nuclear physics research. These works have strongly modified the hydrogeological situation of the chain, as shown by the decrease in flow rate that occurred in many springs located at the border of the carbonatic structure, along the boundary between the permeable limestone of the massif and the surrounding aquicludes. The analysis of the seismicity (M≥ 3.0) that occurred in the Gran Sasso area from 1956 to 1995 suggests that after the tunnelling works both the number of earthquakes has increased and epicenters have migrated, gathering at the northwestern border zone. The foremost events which occurred in this zone in recent years took place on May 5, 1992 (M = 3.1), August 25, 1992 (M = 3.9) and March 13, 1994 (M = 3.5). The flow rate data of four springs and water level data of an underground karst pool located at the border of the carbonatic structure of the massif show clear anomalies before the occurrence of the quoted earthquakes. Regardless, these anomalies can be explained by the rapid melting of the thick mantle of snow on the Gran Sasso chain, due to sudden increases of mean temperatures. In this paper we present and discuss the possibility that the quoted earthquakes are induced by the irregular variations of the Gran Sasso aquifer, evidenced by the quoted anomalies in the flow rate and water level. 相似文献
60.
M. Della Valle M. Kissler-Patig J. Danziger & J. Storm 《Monthly notices of the Royal Astronomical Society》1998,299(1):267-276
We have determined the absolute magnitude at maximum light of SN 1992A by using the turnover magnitude of the globular cluster luminosity function of its parent galaxy, NGC 1380. A recalibration of the peak of the turnover magnitude of the Milky Way clusters using the latest Hipparcos results has been made with an assessment of the complete random and systematic error budget. The following results emerge: a distance to NGC 1380 of 18.6 ± 1.4 Mpc, corresponding to ( m − M ) 31.35 ± 0.16, and an absolute magnitude of SN 1992A at maximum of M B (max) −18.79 ± 0.16. Taken at face value, SN 1992A seems to be more than half a magnitude fainter than the other SNe Ia for which accurate distances exist. We discuss the implications of this result and present possible explanations. We also discuss the Phillips relationship between rate of decline and the absolute magnitude at maximum, on the basis of nine SNe Ia, the individual distances of which have been obtained with Cepheids and the globular cluster luminosity function. The new calibration of this relationship, applied to the most distant SNe of the Calan–Tololo survey, yields H 0 = 62 ± 6 km s−1 Mpc−1 . 相似文献