Improved Monte Carlo inversion of surface wave data

Inversion of surface wave data suffers from solution non‐uniqueness and is hence strongly biased by the initial model. The Monte Carlo approach can handle this non‐uniqueness by evidencing the local minima but it is inefficient for high dimensionality problems and makes use of subjective criteria, such as misfit thresholds, to interpret the results. If a smart sampling of the model parameter space, which exploits scale properties of the modal curves, is introduced the method becomes more efficient and with respect to traditional global search methods it avoids the subjective use of control parameters that are barely related to the physical problem. The results are interpreted drawing inference by means of a statistical test that selects an ensemble of feasible shear wave velocity models according to data quality and model parameterization. Tests on synthetic data demonstrate that the application of scale properties concentrates the sampling of model parameter space in high probability density zones and makes it poorly sensitive to the initial boundary of the model parameters. Tests on synthetic and field data, where boreholes are available, prove that the statistical test selects final results that are consistent with the true model and which are sensitive to data quality. The implemented strategies make the Monte Carlo inversion efficient for practical applications and able to effectively retrieve subsoil models even in complex and challenging situations such as velocity inversions.     

Characterizing high energy explosive eruptions at Stromboli volcano using multidisciplinary data: An example from the 9 January 2005 explosion

Stromboli is well known for its persistent, normal explosive activity, consisting of intermittent, mild to moderate, Strombolian explosions that typically occur every 10–20 min. All tephras erupted during this activity usually fall back into the crater terrace, and consist of volatile-poor scoriae fed by Highly Porphyritic (HP) magma. More occasionally, large explosions or “paroxysms” eject a greater quantity of tephra, mainly consisting of HP scoriae and pumice clasts of Low Porphyritic (LP) magma, but also including large lithic blocks. In addition to this activity, between 2004 and 2006 high energy explosions, displaying an intermediate eruptive style between that of normal and paroxysmal explosions in terms of column height, duration and tephra dispersal, were observed to occur at a frequency of one to eight events per year. While many volcanological, geochemical and geophysical studies have focused in the last few years on the two end-members of activity, i.e. normal or paroxysmal, a detailed investigation on these intermediate types of events has not been carried out yet. Here we report of a study on the 9 January 2005 explosion, one of the high energy explosions during which the main fountaining phase lasted nearly a minute causing ejection of coarse bombs up to a height of 120 m, and of ash and lapilli to > 200 m. An accompanying ash plume rose up to 500 m at the end of the explosion. We present a multidisciplinary approach that integrates the results from analysis of live-camera images with compositional and textural characterization of the erupted products. Major element composition of glassy groundmass and 3D views of textures in the erupted scoriae support the hypothesis based on volcanological observations that this explosion falls between normal and paroxysmal activity, for which we use the term “intermediate”. By comparing the video-camera images of the 9 January 2005 explosion with volcanological features of other high energy explosions that occurred at Stromboli between June 2004 and October 2006, we find that three additional events can be considered intermediate explosions, suggesting that this type of activity may be fairly common on this volcano. The results of this study, although preliminary given our limited dataset, clearly indicate that the methodology used here can be successfully applied to better define the range of eruptive styles typifying the normal explosive activity, potentially improving our capability of eruption forecasting and assessing volcanic hazard at Stromboli.     

A geologically-based approach to map arsenic risk in crystalline aquifers:Analysis of the Tampere region,Finland

The study illustrates the critical role of accurate geological structural mapping to delineate crystalline aquifer zones more prone to high health risk due to elevated dissolved As in drinking wells.The analysis revisits the results from more than 1200 groundwater samples collected over ten years from domestic wells across the Tampere region(Finland).It is demonstrated that the highest dissolved As concentrations in the region(up to 2230 μg/L)are exclusively found near major faults and deformation zones(FDZs)detected via geophysical and geological surveys,and that a clear correlation exists between dissolved concentrations and the distance from the FDZs(r).Almost all values exceeding the drinking water limit(10 μg/L)occur at r8 km,while concentrations above 100 μg/L occur at r4 km.Solidphase As concentrations in bedrock show less dependency on FDZ than aqueous concentrations.This behavior is explained considering different mechanisms,which include enhanced sulfide oxidation and fracture connectivity,promoting preferential transport of dissolved As to FDZs and mixing of waters from different redox zones,mobilizing preferentially As(Ⅲ)or As(V).Fe hydro-oxides may also precipitate/dissolve preferentially because of FDZs,while residence time may influence the contact time between water and As-bearing minerals.It is concluded that the accurate mapping of FDZs,and in general of structural geology,provides an important preliminary information to identify where localized,sitespecific characterization of hydrogeology and geochemistry is more urgent to reduce As-related health risk from groundwater intake.     

Shifting styles of basaltic explosive activity during the 2002–03 eruption of Mt. Etna, Italy

The 2002–03 flank eruption of Etna was characterized by two months of explosive activity that produced copious ash fallout, constituting a major source of hazard and damage over all eastern Sicily. Most of the tephra were erupted from vents at 2750 and 2800 m elevation on the S flank of the volcano, where different eruptive styles alternated. The dominant style of explosive activity consisted of discrete to pulsing magma jets mounted by wide ash plumes, which we refer to as ash-rich jets and plumes. Similarly, ash-rich explosive activity was also briefly observed during the 2001 flank eruption of Etna, but is otherwise fairly uncommon in the recent history of Etna. Here, we describe the features of the 2002–03 explosive activity and compare it with the 2001 eruption in order to characterize ash-rich jets and plumes and their transition with other eruptive styles, including Strombolian and ash explosions, mainly through chemical, componentry and morphology investigations of erupted ash. Past models explain the transition between different styles of basaltic explosive activity only in terms of flow conditions of gas and liquid. Our findings suggest that the abundant presence of a solid phase (microlites) may also control vent degassing and consequent magma fragmentation and eruptive style. In fact, in contrast with the Strombolian or Hawaiian microlite-poor, fluidal, sideromelane clasts, ash-rich jets and plumes produce crystal-rich tachylite clasts with evidence of brittle fragmentation, suggesting that high groundmass crystallinity of the very top part of the magma column may reduce bubble movement while increasing fragmentation efficiency.     

Flare forecasting based on sunspot-groups characteristics

Our comprehension of solar flares is still lacking in many aspects and the possibility of observing active regions during the first phases of flare occurrence is limited by our capability of doing accurate flare forecasting. In order to give a contribution to this aspect, we focused our attention on the characteristics that must be fulfilled by sunspot-groups in order to be flare-productive. We addressed this problem using a statistical approach: first, we analyzed sunspot-groups parameters (i.e., Zürich class, magnetic configuration, area, morphology of the penumbra) and evolution; then, we performed a flare forecasting campaign, based on the results obtained in the first phase and on real-time observations. The results obtained by comparing the flare forecasting probability with the number of flares that have actually occurred are quite encouraging; we plan to improve this procedure by including a bigger statistical sampling.     

A stakeholder consultation into hydro-meteorological e-science environments

The purpose of this paper is to report on and analyse an international consultation into hydro-meteorological e-Science environments with the objective of identifying key functions and features together with exploring show-stopping issues and organisational structure. Transatlantic experiences were compared and contrasted. Including strong participation from both Europe and the USA with high quality responses from experienced practitioners, the consultation was undertaken as part of a joint initiative and took the form of an online questionnaire supported by a set of stakeholder interviews and other discussions. Topics included were functions and features such as provision of numerical models and data, usability, and ease of access; show-stopping issues such as flexibility, reliability and longevity; centralised and distributed structures, and funding models. The results demonstrated a broadly similar set of experiences and implied a future as an evolution of that which exists today. The consultation exercise ran alongside the development of the DRIHM e-Infrastructure which had, in itself, already benefitted from the prior DRIHMS consultation. Results were fed in to the development process at appropriate intervals allowing the consultation to shape the resultant services.     

Diatom response to mid-Holocene climate change in Lago di Massaciuccoli (Tuscany,Italy)

A sedimentary sequence from the Mediterranean coastal basin of Lago di Massaciuccoli (Tuscany, Italy) was analyzed for diatoms, covering two periods over the past ca. 7,000 years. The site was selected because it is situated in a sensitive position at the limit between Mediterranean and Central European climates and biomes. Our focus is on the impact of accelerated human activity during the recent past (water uptake in the catchment, sand extraction, wastewater discharge) and on a phase of evident change between 6,600 and 5,400 cal. BP. The diatom record suggests fresh-water conditions and rather high lake levels until ca. 6,000 years ago. The subsequent shift towards brackish conditions peaked at around 5,500 cal. BP. We relate this shift to a pervasive change towards a drier climate that has been observed elsewhere in the Mediterranean and Northern African regions, and stands in contrast to the shift towards a cooler and more humid climate in the nearby Alps (200–350 km distant) and in central Europe. Pollen and charcoal records from a previous study on the same sedimentary sequence were used to gain additional insights about the causes of the changes in the diatom assemblages and apply numerical methods to search for common trends and correlations.