Contrasting radon background levels in volcanic settings: clues from 220Rn activity concentrations measured during long-term deformation experiments

To better understand the mechanisms leading to different radon background levels in volcanic settings, we have performed two long-term deformation experiments of 16 days using a real-time setup that enables us to monitor any variation of radon activity concentration during rock compression. Our measurements demonstrate that, in the case of highly porous volcanic rocks, the emanating power of the substrate changes as a function of the volcanic stress conditions. Constant magmatic pressures, such as those observed during dike intrusions and hydrothermal fluid injections, can result in pervasive pore collapse that is mirrored by a significant radon decrease until a constant emanation is achieved. Conversely, repeated cycles of stress due to, for example, volcano inflation/deflation cycles, cause a progressive radon increase a few days (but even weeks and months) before rupture. After rock failure, however, the formation of new emanation surfaces leads to a substantial increase of the radon signal. Our results suggest that surface deformation in tectonic and volcanic settings, such as inflation/deflation or constant magmatic pressures, have important repercussions on the emanating power of volcanic substrates.     

Relationships between glacier and rock glacier in the Maritime Alps, Schiantala Valley, Italy

In the Schiantala Valley of the Maritime Alps, the relationship between a till-like body and a contiguous rock glacier has been analyzed using geomorphologic, geoelectric and ice-petrographic methodologies. DC resistivity tomographies undertaken in the till and in the rock glacier show the presence of buried massive ice and ice-rich sediments, respectively. Ice samples from a massive ice outcrop show spherical gas inclusions and equidimensional ice crystals that are randomly orientated, confirming the typical petrographic characteristics of sedimentary ice. The rock glacier formation began after a phase of glacier expansion about 2550 ± 50 ¹⁴C yr BP. Further ice advance during the Little Ice Age (LIA) overrode the rock glacier root and caused partial shrinkage of the pre-existing permafrost. Finally, during the 19th and 20th centuries, the glacial surface became totally debris covered. Geomorphological and geophysical methods combined with analyses of ice structure and fabric can effectively interpret the genesis of landforms in an environment where glaciers and permafrost interact. Ice petrography proved especially useful for differentiating ice of past glaciers versus ice formed under permafrost conditions. These two mechanisms of ice formation are common in the Maritime Alps where many sites of modern rock glaciers were formerly occupied by LIA glaciers.     

The Ñuagapua alluvial fan sequence: Early and Late Holocene human-induced changes in the Bolivian Chaco?

The Quebrada Ñaguapua alluvial fan provides a record of changes that have affected the Bolivian Chaco during the Holocene. The 4th oldest Unit, possibly related to the last glaciation, is restricted to the fan apex; it was deeply dissected during the Early Holocene, with three other units emplaced within the resultant incision. Sandy sediments characterise Unit 1 and 3 while Unit 2 is a forest soil that marks a period of stability. The oldest Unit 1 was deposited just before 6900 years BP. It contains artefacts that represent the earliest evidence of human occupation and suggests that deposition was perhaps induced by deforestation. Anthropogenic deforestation is evident at the base of Unit 3, which contains a wooden plank (140 years BP), charcoal, ash and charred tree-trunks. Some trunks have been burnt in situ while others survived the fire and are still growing, although their roots emanate from Unit 2. Although, similar events slightly to the north have been attributed to climatic changes, the delay in soil erosion in closely spaced areas could be plausibly attributed to human-induced changes. Megafaunal remains in Unit 1 represent the last occurrence of megafauna, including horse, in South America. The faunal association is anomalous because of the concurrent presence of aquatic, forest and open-environment species. We suggest that the last migrated from the southern part of Continent, where ecologic conditions allowed their survival in the Early Holocene, after the widespread clearing of the natural forest and shortly prior to the extinction of the Magafauna.     

Deep 3D thermal modelling for the city of Berlin (Germany)

This study predicts the subsurface temperature distribution of Germany’s capital Berlin. For this purpose, a data-based lithosphere-scale 3D structural model is developed incorporating 21 individual geological units. This model shows a horizontal grid resolution of (500 × 500) m and provides the geometric base for two different approaches of 3D thermal simulations: (1) calculations of the steady-state purely conductive thermal field and (2) simulations of coupled fluid flow and heat transport. The results point out fundamentally different structural and thermal configurations for potential geothermal target units. The top of the Triassic Middle Buntsandstein strongly varies in depth (159–2,470 m below sea level) and predicted temperatures (15–95 °C), mostly because of the complex geometry of the underlying Permian Zechstein salt. The top of the sub-salt Sedimentary Rotliegend is rather flat (2,890–3,785 m below sea level) and reveals temperatures of 85–139 °C. The predicted 70 °C-isotherm is located at depths of about 1,500–2,200 m, cutting the Middle Buntsandstein over large parts of Berlin. The 110 °C-isotherm at 2,900–3,700 m depth widely crosscuts the Sedimentary Rotliegend. Groundwater flow results in subsurface cooling the extent of which is strongly controlled by the geometry and the distribution of the Tertiary Rupelian Clay. The cooling effect is strongest where this clay-rich aquitard is thinnest or missing, thus facilitating deep-reaching forced convective flow. The differences between the purely conductive and coupled models highlight the need for investigations of the complex interrelation of flow- and thermal fields to properly predict temperatures in sedimentary systems.     

A search for the submillimetre counterparts to Lyman break galaxies

We have carried out targeted submillimetre observations as part of a programme to explore the connection between the rest-frame ultraviolet and far-infrared properties of star-forming galaxies at high redshift, which is currently poorly understood. On the one hand, the Lyman break technique is very effective at selecting     galaxies. On the other, 'blank-field' imaging in the submillimetre seems to turn up sources routinely, amongst which some are star-forming galaxies at similar redshifts. Already much work has been done searching for optical identifications of objects detected using the SCUBA instrument. Here we have taken the opposite approach, performing submillimetre photometry for a sample of Lyman break galaxies, the ultraviolet properties of which imply high star formation rates. The total signal from our Lyman break sample is undetected in the submillimetre, at an rms level of ∼0.5 mJy, which implies that the population of Lyman break galaxies does not constitute a large part of the recently detected blank-field submillimetre sources. However, our one detection suggests that with reasonable SCUBA integrations we might expect to detect those few Lyman break galaxies that are far-infrared brightest.     

Dendrogeomorphic reconstruction of past landslide reactivation with seasonal precision: the Bois Noir landslide, southeast French Alps

The purpose of this study was to reconstruct spatiotemporal patterns of past landslide reactivation in a forested area of the Barcelonnette Basin (Bois Noir landslide, Southern French Alps). Analysis of past events was based on tree ring series from 79 heavily affected Mountain pine (Pinus uncinata Mill. ex Mirb) trees growing near or next to the landslide body. Dendrogeomorphic analysis focused on the presence of compression wood and growth reductions, with the first reaction being used for a dating of past reactivations with seasonal precision. A total of 151 growth disturbances were identified in the samples representing eight different stages of reactivation of the landslide body between 1874 and 2008. The spatiotemporal accuracy of the reconstruction is confirmed by historical records from neighboring sites and by aerial photographs. The onset of compression wood formation allows identifying five stages of landslide reactivation during the dormant season or the very beginning of the growing season of trees, i.e., between early October and late May, and three stages toward the end of the growth period. Monthly rainfall data from the HISTALP database demonstrate that the rainfall during four out of the eight reactivations are characterized by summer rainfall totals (July?CAugust) exceeding 200?mm, pointing to the important role of summer rainstorms in the triggering of events at the Bois Noir landslide body.     

Foreword to the special issue on the ITACA strong motion database

The Special Issue of the Bulletin of Earthquake Engineering devoted to the new Italian strong motion database ITACA (ITalian ACelerometric Archive) is introduced in this foreword. An overview of the papers published in this issue is presented, providing an idea of the number of problems encountered in the compilation of a database as rich of information as ITACA, of the solutions adopted and of the possible research and practical applications. Most of the contents, though specifically addressed to ITACA and to its accelerograms, can be usefully thought of as an exemplification of approaches and methods that can be used for, and extended to, similar databases in other countries.     

Quantum-mechanical modeling of minerals at high pressures. The role of the Hamiltonian in a case study: the beryl (Al4Be6Si12O36)

Ab initio calculations of the beryl structure at room and higher pressures, and of its equation of state, have been performed both at the Hartree–Fock (HF) and density functional (DFT) level. In the latter case, three different hybrid HF/DFT Hamiltonians have been employed, in which the exact non-local exchange contribution increases from 20% (B3LYP Hamiltonian, indicated with the symbol F20) to 50% (F50) and 60% (F60). Within the DFT series, the equilibrium volume (V ₀) increases as the HF exchange contribution decreases; with respect to the experimental datum, F20 overestimates V ₀ by 2.9%, whereas F60 underestimates it by 0.9%; F50 (and HF) volume is very close to the experimental datum (error less than −0.1%). All four Hamiltonians overestimate the bulk modulus (K ₀); with respect to the experimental datum (obtained in the present work) [K ₀=179(1) GPa], the F20 Hamiltonian leads to the smallest error (+2.7%); the corresponding errors for the F50, F60 and HF Hamiltonians are +13.2, +16.2 and +16.3%, respectively. In the case of F20, in spite of the small error in K ₀, the relatively large error in V ₀ leads to an incorrect P(V) equation of state, which significantly overestimates the pressure at a given volume, compared to the experimental one at the same volume; the maximum error in the pressure range investigated is at the largest pressure (P _max=26.4 GPa) and amounts to +34.8%. The corresponding errors for the F50, F60 and HF Hamiltonians are +12.9, +5.7 and +15.5%.     

A comparison of surface and underground array measurements of ambient noise recorded in Naples (Italy)

In this study, we describe two experiments of seismic noise measurements carried out in Naples, Italy. The site allowed measurements to be obtained both at the surface and in a tunnel that is 120-m-deep. The main goal was to compare the seismic response evaluated at the surface to the in-tunnel response, through spectral, polarization, and resonance directivity analyses. In the 1 to 20 Hz frequency band, the noise level was up to 15 dB higher at the surface than in the tunnel. The polarization properties and horizontal-to-vertical spectral ratios appear not to be influenced by the tunnel geometry or by the topography. Some preferential alignments were observed in the polarization azimuths computed at the surface, which are likely to be due to local sources, rather than morphological features. The absence of directivity effects and the low noise levels in the tunnel make this site suitable for installing seismic stations. We also studied how the subsoil structure affects the seismic motion at the surface. The dispersive properties of the Rayleigh waves were investigated using the spatial autocorrelation method. A joint inversion of the dispersion data and the horizontal-to-vertical spectral ratios provided the subsurface Vs profile. The derived model has a low velocity contrast at depth, such as to generate moderate and broad H/V spectral ratio peak amplitude. The normalized spectral ratio appears more appropriate to identify the soil-resonance frequencies.