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1.
The rapid decrease of the acceleration spectral amplitude at high frequencies has widely been modeled by the spectral decay factor kappa (κ). Usually, the path-corrected component of κ, often called κ0, is believed to be a local and frequency-independent site characteristic, in turn representing attenuation related to waves propagating vertically through the very shallow layers beneath the study site. Despite the known relevance of κ0 in a wide range of seismological applications, most methods for its calculation do not fully consider the influence of the scattering component. To account for the scattering component, we present a summary of statistical observations of the seismic wavefield at sites of the Swiss seismic networks. The intrinsic properties of the wavefield show a clear dependency on the local shallow subsoil conditions with differences in the structural heterogeneity of the shallow subsoil layers producing different scattering regimes. Such deviations from the ballistic behavior (i.e., direct waves that sample only distinct directions) are indicative for local structural heterogeneities and the associated level of scatter. Albeit the attenuation term related to scattering depends nonlinearly on the intrinsic term, the results indicate that the commonly used explanation for the high-frequency decay spectrum might not be appropriate but involving the amount of scattering might allow better constrained estimates of κ0. 相似文献
2.
Spatio-temporal estimation of precipitation over a region is essential to the modeling of hydrologic processes for water resources management. The changes of magnitude and space–time heterogeneity of rainfall observations make space–time estimation of precipitation a challenging task. In this paper we propose a Box–Cox transformed hierarchical Bayesian multivariate spatio-temporal interpolation method for the skewed response variable. The proposed method is applied to estimate space–time monthly precipitation in the monsoon periods during 1974–2000, and 27-year monthly average precipitation data are obtained from 51 stations in Pakistan. The results of transformed hierarchical Bayesian multivariate spatio-temporal interpolation are compared to those of non-transformed hierarchical Bayesian interpolation by using cross-validation. The software developed by [11] is used for Bayesian non-stationary multivariate space–time interpolation. It is observed that the transformed hierarchical Bayesian method provides more accuracy than the non-transformed hierarchical Bayesian method. 相似文献
3.
Correlations of seismic noise are commonly used to monitor temporal variations of relative seismic velocity in period ranges from 1 s up to 100 s. Of particular interest is the detection of small changes in the order of 0.01–0.1 % in propagation speeds. Measuring such small differences can, however, be significantly biased by temporal variations in the properties of the noise sources within the corresponding frequency band. Using synthetic data, we show that apparent relative velocity variations might appear only due to changes in the amplitude and frequency content caused by source variations. Removing such unwanted effects by applying narrow bandpass filters in the preprocessing restricts the high-resolution analysis of any signal due to Gabor’s uncertainty limit, i.e., the correlation function suffers a limited resolution to time delay estimates for small correlation times, low-frequency ranges, and in narrow frequency bands. Better understanding of spatiotemporal noise source properties and the theoretical limitations of time–frequency analysis is critical for accurate and reliable passive monitoring. 相似文献
4.
A. Myrttinen V. Becker M. Nowak M. Zimmer P. Pilz J. A. C. Barth 《Environmental Earth Sciences》2012,67(2):473-479
Baseline monitoring at the proposed enhanced gas recovery site in Altmark (Germany) was carried out in combination with theoretical and laboratory investigations to describe and predict the principles of expected stable carbon isotope and dissolved inorganic carbon (DIC) trends during CO2 injection in reservoirs. This provides fundamental data for site-specific characterisation for monitoring purposes. Baseline ??13C values at the Altmark site ranged between ?1.8 and ?11.5??? and DIC values were about 2?mmol?L?1. These baseline values form the basis for a theoretical study on the influences of the ambient reservoir conditions on the state of geochemical and isotope equilibrium of the reservoir fluids. Transferring this theoretical study to the Altmark site enables predictions on geochemical trends during potential injection. Assuming that CO2 would be injected at the Altmark site to pCO2?=?100?bar and with a ??13C of ?30???, at isotopic and geochemical equilibrium, ??13CDIC values would approach this end-member, and DIC concentrations of 1,000?mmol L?1 would be expected. Laboratory experiments were conducted at low pCO2 levels (4?C35?bars) to mimic the approach of a CO2 plume at a monitoring well. These results support field investigations from other sites: that ??13CDIC is a sensitive tool for monitoring CO2 migration in the subsurface and simultaneously allows quantification of geochemical trapping of CO2. 相似文献
5.
Michael Kühn Maja Tesmer Peter Pilz Robert Meyer Kurt Reinicke Andrea F?rster Olaf Kolditz Dirk Sch?fer 《Environmental Earth Sciences》2012,67(2):311-321
The joint research project CLEAN was conducted in the years 2008?C2011 by a German research and development (R&D) alliance of 16 partners from science and industry. The project was set-up as pilot project to investigate the processes relevant to enhanced gas recovery (EGR) by the injection of CO2 into a subfield of the almost depleted Altmark natural gas field. Despite the setback that permission for active injection was not issued by the mining authority during the period of the project, important results fostering the understanding of processes linked with EGR were achieved. Work carried out led to a comprehensive evaluation of the EGR potential of the Altmark field and the Altensalzwedel subfield in particular. The calculated safety margins emphasize that technical well integrity of the 12 examined boreholes is given for EGR without a need for any further intervention. The laboratory and field tests confirm that the Altensalzwedel subfield is suitable for the injection of 100,000?t of CO2. Numerical simulations provide sound predictions for the efficiency and safety of the EGR technology based on the CO2 injection. The development and testing of different monitoring techniques facilitate an improved surveying of CO2 storage sites in general. The CLEAN results provide the technological, logistic and conceptual prerequisites for implementing a CO2-based EGR project in the Altmark and provide a benchmark for similar projects in the world. 相似文献
6.
The increasing physical and technical demands placed on construction materials, especially as they are being used more and
more up to the limits of their mechanical strength, has led the aggregates industry to search for more efficient methods of
quality control. Information from theoretical work on rock spectra in near-infrared and mid-infrared light as well as achievements
gained in signal processing can all be used to improve quality control in an economically acceptable manner. As engineering
properties of aggregates are to a great extent determined by the petrological composition of the rock aggregates, the question
is, whether a statistical classification rule for identification of rock aggregates can be developed. However, the classification
of rocks is complicated by the fact that the optical behavior of minerals forming the rock often appears muted. In addition,
minor constituents may dominate the spectrum. Furthermore, the relevant spectra form high dimensional data that are extremely
difficult to analyze statistically, especially when curves are very similar. In this paper, support vector machines for classification
of rock spectra are investigated, since they are appropriate in classifying highly dimensional data such as spectra. 相似文献
7.
F. Bergamaschi G. Cultrera L. Luzi R. M. Azzara G. Ameri P. Augliera P. Bordoni F. Cara R. Cogliano E. D��Alema D. Di Giacomo G. Di Giulio A. Fodarella G. Franceschina F. Galadini M. R. Gallipoli S. Gori P. Harabaglia C. Ladina S. Lovati S. Marzorati M. Massa G. Milana M. Mucciarelli F. Pacor S. Parolai M. Picozzi M. Pilz S. Pucillo R. Puglia G. Riccio M. Sobiesiak 《Bulletin of Earthquake Engineering》2011,9(3):697-715
A temporary network of 33 seismic stations was deployed in the area struck by the 6th April 2009, Mw 6.1 (Scognamiglio et?al. in Seism Res Lett 6/81, 2010), L??Aquila earthquake (central Italy), with the aim to investigate the site amplification within the Aterno river Valley. The seismograms of 18 earthquakes recorded by 14 of the 33 stations were used to evaluate the average horizontal to vertical spectral ratio (HVSR) for each site and the standard horizontal spectral ratio (SSR) between a site and a reference station. The obtained results have been compared to the geological and geophysical information in order to explain the resonance frequencies and the amplification levels with respect to surface geology of the valley. The results indicate that there is no uniform pattern of amplification, because of the complex geologic setting, as the thickness and degree of cementation of the deposits is highly variable. 相似文献
8.
9.
Bernd Wiese Martin Zimmer Martin Nowak Linda Pellizzari Peter Pilz 《Environmental Earth Sciences》2013,70(8):3709-3726
In order to detect hydraulic and geochemical impact on the groundwater directly above the CO2 storage reservoir at the Ketzin pilot site continuous monitoring using an observation well is carried out. The target depth (446 m below ground level, bgl.) of the well is the Exter formation (Upper Triassic, Rhaetian) which is the closest permeable stratigraphic overlying formation to the CO2 storage reservoir (630–636 m bgl. at well location). The monitoring concept comprises evaluation of hydraulic conditions, temperature, water chemistry, gas geochemistry and δ13C values. This is achieved by a tubing inserted inside the well with installed pressure sensors and a U-tube sampling system so that pumping tests or additional wireline logging can be carried out simultaneously with monitoring. The aquifer was examined using a pump test. The observation well is hydraulically connected to the regional aquifer system and the permeability of about 1.8 D is comparatively high. Between Sept. 2011 and Oct. 2012, a pressure increase of 7.4 kPa is observed during monitoring under environmental conditions. Drilling was carried out with drilling mud on carbonate basis. The concentration of residual drilling mud decreases during the pump test, but all samples show a residual concentration of drilling mud. The formation fluid composition is recalculated with PHREEQC and is comparable to the literature values for the Exter formation. The gas partial pressure is below saturation at standard conditions and the composition is dominated by N2 similar to the underlying storage reservoir prior to CO2 injection. The impact of residual drilling mud on dissolved inorganic carbon and the respective δ13C values decreases during the monitoring period. The pristine isotopic composition cannot be determined due to calcite precipitation. No conclusive results indicate a leakage from the underlying CO2 storage reservoir. 相似文献
10.
Spatial sampling design and covariance-robust minimax prediction based on convex design ideas 总被引：2，自引：2，他引：0
Gunter Spöck Jürgen Pilz 《Stochastic Environmental Research and Risk Assessment (SERRA)》2010,24(3):463-482
This paper presents new ideas on sampling design and minimax prediction in a geostatistical model setting. Both presented
methodologies are based on regression design ideas. For this reason the appendix of this paper gives an introduction to optimum
Bayesian experimental design theory for linear regression models with uncorrelated errors. The presented methodologies and
algorithms are then applied to the spatial setting of correlated random fields. To be specific, in Sect. 1 we will approximate an isotropic random field by means of a regression model with a large number of regression functions
with random amplitudes, similarly to Fedorov and Flanagan (J Combat Inf Syst Sci: 23, 1997). These authors make use of the
Karhunen Loeve approximation of the isotropic random field. We use the so-called polar spectral approximation instead; i.e.
we approximate the isotropic random field by means of a regression model with sine-cosine-Bessel surface harmonics with random
amplitudes and then, in accordance with Fedorov and Flanagan (J Combat Inf Syst Sci: 23, 1997), apply standard Bayesian experimental
design algorithms to the resulting Bayesian regression model. Section 2 deals with minimax prediction when the covariance function is known to vary in some set of a priori plausible covariance
functions. Using a minimax theorem due to Sion (Pac J Math 8:171–176, 1958) we are able to formulate the minimax problem as
being equivalent to an optimum experimental design problem, too. This makes the whole experimental design apparatus available
for finding minimax kriging predictors. Furthermore some hints are given, how the approach to spatial sampling design with
one a priori fixed covariance function may be extended by means of minimax kriging to a whole set of a priori plausible covariance
functions such that the resulting designs are robust. The theoretical developments are illustrated with two examples taken
from radiological monitoring and soil science. 相似文献