1,088 research outputs found
Identification of lateral discontinuities via multi-offset phase analysis of surface wave data
Surface wave methods are based on the inversion of observed Rayleigh wave phase-velocity dispersion curves. The goal is to estimate mainly the shear-wave velocity profile of the investigated site. The model used for the interpretation is 1D, hence results obtained wherever lateral variations are present cannot be considered reliable.In this paper, we study four synthetic models, all with a lateral heterogeneity. When we process the entire corresponding seismograms with traditional f-. k approach, the resulting 1D profiles are representative of the subsurface properties averaged over the whole length of the receivers lines. These results show that classical analysis disregards evidences of sharp lateral velocity changes even when they show up in the raw seismograms.In our research, we implement and test over the same synthetic models, a novel robust automated method to check the appropriateness of 1D model assumption and locate the discontinuities. This new approach is a development of the recent multi-offset phase analysis with the following further advantages: it does not need previous noise evaluation and more than one shot.Only once the discontinuities are clearly identified, we confidently perform classical f-k dispersion curve extraction and inversion separately on both sides of the discontinuity. Thus the final results, obtained by putting side by side the 1D profiles, are correct 2D reconstructions of the discontinuous S-wave distributions obtained without any additional ad-hoc hypotheses
Focusing inversion techniques applied to electrical resistance tomography in an experimental tank
We present an algorithm for focusing inversion of electrical resistivity
tomography (ERT) data. ERT is a typical example of ill-posed problem.
Regularization is the most common way to face this kind of problems; it
basically consists in using a priori information about targets to reduce the
ambiguity and the instability of the solution. By using the minimum gradient
support (MGS) stabilizing functional, we introduce the following geometrical
prior information in the reconstruction process: anomalies have sharp
boundaries. The presented work is embedded in a project (L.A.R.A.) which aims
at the estimation of hydrogeological properties from geophysical
investigations. L.A.R.A. facilities include a simulation tank (4 m x 8 m x 1.35
m); 160 electrodes are located all around the tank and used for 3-D ERT.
Because of the large number of electrodes and their dimensions, it is important
to model their effect in order to correctly evaluate the electrical system
response. The forward modelling in the presented algorithm is based on the
so-called complete electrode model that takes into account the presence of the
electrodes and their contact impedances. In this paper, we compare the results
obtained with different regularizing functionals applied on a synthetic model.Comment: 4 pages, 7 figures, to appear in the Proceedings of Int. Assoc. for
Mathematical Geology XI International Congres
Focusing inversion techniques applied to electrical resistance tomography in an experimental tank
We present an algorithm for focusing inversion of electrical resistivity
tomography (ERT) data. ERT is a typical example of ill-posed problem. Regularization is the
most common way to face this kind of problems; it basically consists in using a priori
information about targets to reduce the ambiguity and the instability of the solution. By using
the minimum gradient support (MGS) stabilizing functional, we introduce the following
geometrical prior information in the reconstruction process: anomalies have sharp boundaries.
The presented work is embedded in a project (L.A.R.A.) which aims at the estimation of
hydrogeological properties from geophysical investigations. L.A.R.A. facilities include a
simulation tank (4 m x 8 m x 1.35 m); 160 electrodes are located all around the tank and used
for 3-D ERT. Because of the large number of electrodes and their dimensions, it is important
to model their effect in order to correctly evaluate the electrical system response. The forward
modelling in the presented algorithm is based on the so-called complete electrode model that
takes into account the presence of the electrodes and their contact impedances.
In this paper, we compare the results obtained with different regularizing functionals applied
on a synthetic model
Focusing inversion technique applied to radar tomographic data
Traveltime tomography is a very effective tool to reconstruct acoustic,
seismic or electromagnetic wave speed distribution. To infer the velocity image
of the medium from the measurements of first arrivals is a typical example of
ill-posed problem. In the framework of Tikhonov regularization theory, in order
to replace an ill-posed problem by a well-posed one and to get a unique and
stable solution, a stabilizing functional (stabilizer) has to be introduced.
The stabilizer selects the desired solution from a class of solutions with a
specific physical and/or geometrical property; e.g., the existence of sharp
boundaries separating media with different petrophysical parameters. Usually
stabilizers based on maximum smoothness criteria are used during the inversion
process; in these cases the solutions provide smooth images which, in many
situations, do not describe the examined objects properly. Recently a new
algorithm of direct minimization of the Tikhonov parametric functional with
minimum support stabilizer has been introduced; it produces clear and focused
images of targets with sharp boundaries. In this research we apply this new
technique to real radar tomographic data and we compare the obtained result
with the solution generated by the more traditional minimum norm stabilizer.Comment: 4 pages, 1 figur
Multiple-point statistical simulation for hydrogeological models: 3D training image development and conditioning strategies
Most studies about the application of geostatistical simulations based on multiple-point statistics (MPS) to hydrogeological modelling focus on relatively fine-scale models and concentrate on the estimation of facies-level, structural uncertainty. Much less attention is paid to the use of input data and optimal construction of training images. For instance, even though the training image should capture a set of spatial geological characteristics to guide the simulations, the majority of the research still relies on 2D or quasi-3D training images. In the present study, we demonstrate a novel strategy for 3D MPS modelling characterized by: (i) realistic 3D training images, and (ii) an effective workflow for incorporating a diverse group of geological and geophysical data sets. The study covers an area of 2810 km2 in the southern part of Denmark. MPS simulations are performed on a subset of the geological succession (the lower to middle Miocene sediments) which is characterized by relatively uniform structures and dominated by sand and clay. The simulated domain is large and each of the geostatistical realizations contains approximately 45 million voxels with size 100 m × 100 m × 5 m. Data used for the modelling include water well logs, high-resolution seismic data, and a previously published 3D geological model. We apply a series of different strategies for the simulations based on data quality, and develop a novel method to effectively create observed sand/clay spatial trends. The training image is constructed as a small 3D voxel model covering an area of 90 km2. We use an iterative training image development strategy and find that even slight modifications in the training image create significant changes in simulations. Thus, the study underlines that it is important to consider both the geological environment, and the type and quality of input information in order to achieve optimal results from MPS modelling. In this study we present a possible workflow to build the training image and effectively handle different types of input information to perform large-scale geostatistical modellin
Seismic vulnerability analysis for masonry hospital structures: Expeditious and detailed methods
Measuring and modeling water-related soil-vegetation feedbacks in a fallow plot
Abstract. Land fallowing is one possible response to shortage of water for irrigation. Leaving the soil unseeded implies a change of the soil functioning that has an impact on the water cycle. The development of a soil crust in the open spaces between the patterns of grass weed affects the soil properties and the field-scale water balance. The objectives of this study are to test the potential of integrated non-invasive geophysical methods and ground-image analysis and to quantify the effect of the soil–vegetation interaction on the water balance of fallow land at the local- and plot scale. We measured repeatedly in space and time local soil saturation and vegetation cover over two small plots located in southern Sardinia, Italy, during a controlled irrigation experiment. One plot was left unseeded and the other was cultivated. The comparative analysis of ERT maps of soil moisture evidenced a considerably different hydrologic response to irrigation of the two plots. Local measurements of soil saturation and vegetation cover were repeated in space to evidence a positive feedback between weed growth and infiltration at the fallow plot. A simple bucket model captured the different soil moisture dynamics at the two plots during the infiltration experiment and was used to estimate the impact of the soil vegetation feedback on the yearly water balance at the fallow site
How workers' emotional dissonance explains the association between customers' relations, burnout and health in an Italian supermarket chain
Economic Uncertainty and Fertility in Europe: Narratives of the Future
Background: In the last decade fertility rates have declined in most European countries, and explanations have tended to focus on the rise of economic uncertainty after the Great Recession. The empirical demographic tradition operationalized the forces of economic uncertainty through objective indicators of individuals’ labor market situation; for example, holding a temporary contract or being unemployed. However, contemporary European fertility trends are not comprehensively captured by these traditional indicators and statistical models, because fertility decisions are not a mere “statistical shadow of the past”. Objective: We propose a novel framework on economic uncertainty and fertility. This framework proffers that the conceptualization and operationalization of economic uncertainty needs to take into account that people use works of imagination, producing their own “narrative of the future” – namely, imagined futures embedded in social elements and their interactions. Narratives of the future allow people to act according to or in spite of the uncertainty they face, irrespective of structural constraints and their subjective perceptions. Contribution: In this reflection we suggest that the focus of contemporary fertility studies should partly shift to assessing how people build their narratives of the future. To this end, we propose several methodological strategies to empirically assess the role of narratives for fertility decisions. Future studies should also take into account that personal narratives are shaped by the “shared narratives” produced by several agents of socialization, such as parents and peers, as well as by the narratives produced by the media and other powerful opinion formers
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