Impact of Monthly Radioxenon Source Time-Resolution on Atmospheric Concentration Predictions

The general characterisation of the global radioxenon background is of interest for the verification of the Comprehensive Nuclear-Test-Ban Treaty. Since the major background sources are only a few isotope production facilities, their source term has an emphasized influence on the worldwide monitoring process of radioxenon. In this work, two different datasets of source terms are applied through atmospheric transport modelling, to estimate the concentration at two radioxenon detection stations in Germany and Sweden. One dataset relies on estimated average annual emissions; the other includes monthly resolved measurements from an isotope production facility in Fleurus, Belgium. The quality of the estimations is then validated by comparing them to the radioxenon concentrations that have been sampled at two monitoring stations over the course of 1 year.     

Modeling and visualizing uncertainties of flood boundary delineation: algorithm for slope and DEM resolution dependencies of 1D hydraulic models

As flood inundation risk maps have become a central piece of information for both urban and risk management planning, also a need to assess the accuracies and uncertainties of these maps has emerged. Most maps show the inundation boundaries as crisp lines on visually appealing maps, whereby many planners and decision makers, among others, automatically believe the boundaries are both accurate and reliable. However, as this study shows, probably all such maps, even those that are based on high-resolution digital elevation models (DEMs), have immanent uncertainties which can be directly related to both DEM resolution and the steepness of terrain slopes perpendicular to the river flow direction. Based on a number of degenerated DEMs, covering areas along the Eskilstuna River, Sweden, these uncertainties have been quantified into an empirically-derived disparity distance equation, yielding values of distance between true and modeled inundation boundary location. Using the inundation polygon, the DEM, a value representing the DEM resolution, and the desired level of confidence as inputs in a new-developed algorithm that utilizes the disparity distance equation, the slope and DEM dependent uncertainties can be directly visualized on a map. The implications of this strategy should benefit planning and help reduce high costs of floods where infrastructure, etc., have been placed in flood-prone areas without enough consideration of map uncertainties.     

Calendar time interpolation of amplitude maps from 4D seismic data

A calendar time interpolation method for 2D seismic amplitude maps, done in two steps, is presented. The contour interpolation part is formulated as a quadratic programming problem, whereas the amplitude value interpolation is based on a conditional probability formulation. The method is applied on field data from the Sleipner CO₂ storage project. The output is a continuous image (movie) of the CO₂ plume. Besides visualization, the output can be used to better couple 4D seismic to other types of data acquired. The interpolation uncertainty increases with the time gap between consecutive seismic surveys and is estimated by leaving a survey out (blind test). Errors from such tests can be used to identify problems in understanding the flow and possibly improve the interpolation scheme for a given case. Field‐life cost of various acquisition systems and repeat frequencies are linked to the time‐lapse interpolation errors. The error in interpolated amplitudes increased by 3%‐4% per year of interpolation gap for the Sleipner case. Interpolation can never fully replace measurements.     

Artificial neural networks for removal of couplings in airborne transient electromagnetic data

Modern airborne transient electromagnetic surveys typically produce datasets of thousands of line kilometres, requiring careful data processing in order to extract as much and as reliable information as possible. When surveys are flown in populated areas, data processing becomes particularly time consuming since the acquired data are contaminated by couplings to man‐made conductors (power lines, fences, pipes, etc.). Coupled soundings must be removed from the dataset prior to inversion, and this is a process that is difficult to automate. The signature of couplings can be both subtle and difficult to describe in mathematical terms, rendering removal of couplings mostly an expensive manual task for an experienced geophysicist. Here, we try to automate the process of removing couplings by means of an artificial neural network. We train an artificial neural network to recognize coupled soundings in manually processed reference data, and we use this network to identify couplings in other data. The approach provides a significant reduction in the time required for data processing since one can directly apply the network to the raw data. We describe the neural network put to use and present the inputs and normalizations required for maximizing its effectiveness. We further demonstrate and assess the training state and performance of the network before finally comparing inversions based on unprocessed data, manually processed data, and artificial neural network automatically processed data. The results show that a well‐trained network can produce high‐quality processing of airborne transient electromagnetic data, which is either ready for inversion or in need of minimal manual processing. We conclude that the use of artificial neural network scan significantly reduce the processing time and its costs by as much as 50%.     

Experimental modelling of shallow magma emplacement: Application to saucer-shaped intrusions

Saucer-shaped dolerite and sandstone intrusions are common in sedimentary basins world-wide. We have conducted a series of scaled experiments simulating the process of magma emplacement in sedimentary basins, with particular attention on the formation of saucer-shaped sills. The model materials were (1) cohesive fine-grained silica flour, representing brittle crust; and (2) molten low-viscosity oil, representing magma. The experiments were performed in both homogeneous and layered models. In all the experiments, oil injection resulted in doming of the surface. In the homogeneous models, the injected oil formed cone sheets and sub-vertical dykes. Cone sheets formed for shallow injection (1–3 cm), and vertical dykes formed for deeper injection (4–5 cm). In layered models, the injected oil always formed saucer-shaped intrusions. Our experimental results show that (1) sill intrusion results in the formation of a dome, with melt erupting at the rim; (2) layering controls the formation of sills and saucer-shaped sills; (3) saucer-shaped sills are fed from the bottom and the fluid flows upward and outward; and (4) the diameter of saucer-shaped sills increase with increasing emplacement depth. The systematic relation between domes and sills and the depth-dependence of sill diameters show that saucer-shaped intrusions result from the interaction between a growing flat-lying shallow sill and doming of the free surface. We conclude that saucer-shaped intrusions represent fundamental geometries formed by shallow magma intrusion in stratified basins.     

Wave barrier of lime–cement columns against train-induced ground-borne vibrations

This paper presents a comparison between measured train-induced ground vibrations in the free-field before and after countermeasures had been taken at Kåhög near Gothenburg in Sweden. A wave barrier of lime–cement columns was constructed parallel to the railway in order to reduce the ground-borne vibrations inside nearby buildings. On top of the barrier an embankment was built to reduce air-borne vibrations. Due to the wave barrier design, part of the energy content of the waves was expected to be reflected by the screen and transmitted energy was expected to be partly scattered. Contribution from the noise-embankment was not thought likely but could not be ruled out due to its fairly large mass and its close proximity to the railway. The effect of the mitigating measures resulted in a 67% reduction of the maximum particle velocity at 30 m and 41% at 60 m from the railway. A simple two-dimensional finite element model has been used to study the relative importance of the wave barrier and the noise-embankment as contributors to the mitigation recorded of the ground vibrations in the field. It is concluded with respect to ground vibrations that both the barrier and the embankment had a mitigating effect but that the contribution from the barrier dominated. Furthermore, it is seen from the field results as well as the simulation that the effect of the mitigating action is reduced with increasing distance from the railway.     

Comparison of geotechnical uncertainties linked to different soil characterization methods

One of the essential inputs in settlement prediction models is the soil modulus, which may be obtained from laboratory tests or estimated from in situ measurements. The total uncertainty in predicting the confined modulus of a sandy soil is quantified with data from side-by-side in situ testing using the standard penetration test, the static cone penetration test, the light dynamic probing and the laboratory oedometer test. To estimate transformation errors, correlations are proposed between in situ and laboratory data. The results indicate that similar magnitudes of total uncertainties are associated with the in situ methods, which are approximately twice as high as those from the direct oedometer method. The quantified uncertainties are an important input for reliability-based designs of foundations under similar soil conditions.     

The impacts of a Laki-like eruption on the present Swedish society

In this study, we analyse and discuss the possible impacts on the Swedish society of a volcanic eruption on Iceland, emitting ash particles and large quantities of sulphur dioxide. A scenario was developed, based on the historical Laki eruption of 1783–1784, to describe the content of a potential sulphur fog over time in Sweden. Due to its high complexity and the many uncertainties in the underpinning scientific data, the scenario was developed using a cross-disciplinary approach incorporating experts from different scientific fields. An analysis of the impacts of the hazard on human health, environment and technical equipment was then performed and, finally, representatives from national authorities assessed the overall societal challenges in responding to the consequences of a massive volcanic eruption. The analysis shows that it is the peak concentrations of sulphur dioxide and sulphuric acid rather than the longer periods of moderate concentrations that contribute most to the negative consequences for human health and environment. Altogether, three societal challenges were identified: the ability to compile and disseminate relevant information fast enough, to perform continuous measurements of concentrations of different substances in affected areas and to meet the large demand for medical care.