Role of the backstop-to-cover thickness ratio on vergence partitioning in experimental thrust wedges

The ratio between the thickness of the sedimentary sequences offscraped from the subducting plate ( H _c) and the average thickness of the backstop ( H _b) is expected to significantly influence vergence partitioning in thrust wedges. A series of simple sandbox experiments was performed to study the role of the H _c/ H _b ratio in model thrust wedges. The results obtained show that thrust wedges with H _c/ H _b values lower than 1 are essentially pro-ward verging, with minor retro-ward faulting; H _c/ H _b values greater than 1 imply an increase of vergence partitioning. When a threshold value is exceeded, fully partitioned, doubly vergent thrust wedges develop. Comparison with natural submarine thrust wedges suggests that these experimental results may provide useful insights on the evolution of structural architecture at convergent margins.     

LIDAR monitoring of mass wasting processes: The Radicofani landslide, Province of Siena, Central Italy

The Radicofani Basin, stretching about 30 km NW–SE, is an intra-Central Apennine basin connected to Pliocene–Pleistocene extensional tectonics. It consists of an Early to Middle Pliocene succession including essentially shelf pelites. In the Radicofani area, province of Siena (Tuscany region), morphodynamic processes are very frequent with widespread badlands and rapidly evolving mudflows. In order to evaluate the general instability of the Radicofani area, geological and geomorphological surveys were carried out. The 1954, 1990 and 2003 aerial surveys allowed a comparison of the changes in the various morphological aspects of the study area, which suggested an increase in slope instability with time. A new complex translational landslide evolving into mudflows, activated during the winter of 2003, was monitored using an experimental system based on terrestrial LIDAR (Light Detection and Ranging) and GPS (Global Positioning System) technologies. This system allowed the monitoring of the morphologic and volumetric evolution of the landslide. A comparison of the monitoring data of October 2004, June 2005, May 2006 and May 2007 points out that the evolution is characterised by the sliding of displaced materials. A volume of about 1300 m³ of materials was removed during the period 2004–2005, 300 m³ for 2005–2006, and 400 m³ for 2006–2007. The greater initial mass movement probably reflects a greater static imbalance during the early period of landslide movement and increased rainfall. Therefore, the proposed monitoring system methodology allows the numerical evaluation of the landslide morphological evolution and to validate the landslide evolution model based on geological and geomorphological field surveys.     

Seismic response of multi‐span simply supported bridges to a spatially varying earthquake ground motion

This paper carries out a parametrical study of the pounding phenomenon associated with the seismic response of multi‐span simply supported bridges with base isolation devices. In particular, the analyses focus on the causal relationship between pounding and the properties of a spatially varying earthquake ground motion. In order to include the effect of the torsional component of pounding forces on the seismic response of the whole structure, a three‐dimensional (3D) finite element model has been defined and 3D non‐linear time‐history analyses have been performed. A parametrical study on the size of the gaps between adjacent bridge decks has highlighted that the pounding effects are amplified when the spatially varying ground motion time histories at each support are considered. Because of a spatially varying input, the pounding forces can assume values 3–4 times larger than those derived by a conventional seismic analysis with uniform input or with spatial input but considering ground motion wave passage effect only. The numerical results show that in order to achieve an acceptably safe structural performance during seismic events, a correct design of the isolation devices should take into account the relative displacements calculated by means of a non‐linear time‐history analysis with multi‐support excitation. Copyright © 2002 John Wiley & Sons, Ltd.     

Neotectonics and seismic hazard assessment in Hengchun Peninsula,southern Taiwan

Neotectonic data may indicate whether stored elastic energy will be dissipated or released destructively. The Hengchun Peninsula of Taiwan is the southern extremity of the Central Range of Taiwan and thus an emergent part of the accretionary wedge resulting from subduction of Eurasia beneath the Philippine Sea plate at the Manila Trench. Radiocarbon dating of fossil shorelines on the peninsula shows that it has been uplifted at an average rate of 3.8 mm/yr during the Holocene. About $1/3$ of the uplift is due to deformation along the Hengchun reverse fault but, in contrast with the Chelungpu and other low angle reverse faults west of the Central Range, it accommodates strain principally by aseismic creep. To cite this article: C. Vita-Finzi, J.-C. Lin, C. R. Geoscience 337 (2005).     

A New Ionosphere Monitoring Technology Based on GPS

Although global positioning system (GPS) was originally planned as a satellite-based radio-navigation system for military purposes, civilian users have significantly increased their access to the system for both, commercial and scientific applications. Almost 400 permanent GPS tracking stations have been stablished around the globe with the main purpose of supporting scientific research. In addition, several GPS receivers on board of low Earth orbit satellites fitted with special antennas that focus on Earth's horizon, are tracking the radio signals broadcasted by the high-orbiting GPS satellites, as they rise and set on Earth horizon. The data of these ground and space-born GPS receivers, readily accessible through Internet in a ‘virtual observatory’ managed by the International GPS Service, are extensively used for many researches and might possibly ignite a revolution in Earth remote sensing. By measuring the changes in the time it takes for the GPS signals to arrive at the receiver as they travel through Earth's atmosphere, scientists can derive a surprising amount of information about the Earth's ionosphere, a turbulent shroud of charged particles that, when stimulated by solar flares, can disrupt communications around the world. This contribution presents a methodology to obtain high temporal resolution images of the ionospheric electron content that lead to two-dimensional vertical total electron content maps and three-dimensional electron density distribution. Some exemplifying results are shown at the end of the paper.     

Global nature of the Paleoproterozoic Lomagundi carbon isotope excursion: A review of occurrences in Brazil,India, and Uruguay

Positive carbon isotope excursion is reported from Paleoproterozoic carbonates of the Aravalli Supergroup (northwestern India), the Minas Supergroup (Brazil), and new sections of the Paso Severino Formation (Uruguay). The 2.42 Ga Gandarela Formation, Minas Gerais, Brazil, contains red carbonate-facies BIF grading into dolostones and limestones and yielding δ¹³C values ranging from −1.6 to +0.4‰ V-PDB. The positive C-isotope excursion (up to + 11‰ V-PDB) in marine shallow-water carbonates in India and Brazil (Jhamarkotra Formation in northwestern India, and Cercadinho and Fecho do Funil formations in Minas Gerais State, Brazil) is comparable to that observed in 2.22–2.1 Ga carbonate successions worldwide that were deposited during the Lomagundi excursion. In Uruguay, δ¹³C values up to +11.6‰ V-PDB in the deep-water Paso Severino Formation of the Piedra Alta Terrane are compatible with deposition at ca. 2.15 Ga, as indicated by the 2146 ± 7 Ma U–Pb age of dacites occurring at the top of the unit. Negative δ¹³C values are also present in carbonates of the Paso Severino Formation, but an origin related to organic-matter remineralization cannot be ruled out. Thin carbonate beds in the Rio Itapicuru greenstone belt, Bahia State, Brazil, are associated, as in the Paso Severino Formation, with deep-water black shales and have carbon isotope values up to +9‰ V-PDB. High metamorphic grade carbonates of the Jacurici terrane in the Medrado-Ipueira area, Bahia, Brazil, have carbon isotope values up to +6.9‰ V-PDB, consistent with their minimum age of 2085 ± 5 Ma inferred from the intrusive contact with and the age of the Medrado norite. No evidence was found in India, Brazil, or Uruguay for Paleoproterozoic glacial events recognized in the 2.45–2.22 Ga sedimentary successions worldwide. Unconformities between the Gandarela and Cercadinho formations in Brazil and the banded gneissic Complex and the Lower Aravalli Supergroup in India might explain the absence of glacial record. Compositional and isotopic data presented here for studied Paleoproterozoic carbonate successions allow their integration into the global record of the Paleoproterozoic evolution as well as correlation with other successions of similar age. The study highlights the global nature of the Lomagundi excursion. Furthermore, it indicates that the Lomagundi excursion is recorded in both shallow-water (Aravalli and Minas supergroups) and deep-water carbonates (Paso Severino Formation and Rio Itapicuru greenstone belt) negating a significant impact of stromatolite productivity and hypersaline conditions on carbon isotope values of carbonates deposited in shallow-water, open-marine and isolated basins.     

Improving school children’s understanding of water scarcity with a co-produced book on groundwater in Central Chile

Water scarcity is a critical issue worldwide, and Chile is no exception. Since 2010, Central Chile has been enduring an ongoing water crisis due to the coupled effects of a severe drought and the overuse of water resources, especially groundwater. Rural communities have been strongly impacted, mainly because wells from which drinking water is supplied show a dramatic drop in water levels, and some have even dried up. The water scarcity scenario requires the integration of actors and disciplines to increase awareness of groundwater; however, how to make this valuable element visible in society is an issue that remains open to debate. This paper describes and reflects on the process of making educational material about groundwater and water scarcity for children to promote public awareness. Based on transdisciplinary and co-designing processes, this work describes the social perceptions of groundwater among children and community leaders, as well as how scientific information and local knowledge of water scarcity could be integrated into a book for the young population. This research finds that educational projects on groundwater resources increase people’s awareness of the role of this hidden resource in the water cycle. Such projects encourage the creation of grounded and contextualised materials that incorporate the knowledge and experience already present in the communities, increasing public awareness of the role of groundwater and associated water scarcity issues, thereby integrating academia and society. This approach could be a tool to lay the foundations for successfully addressing the water crisis in Chile over generations.

     

Flotation of galena. Influence of grain size,of pulp deoxygenation,and of cleaning with ammonium acetate

The flotation of < 10, 10–20, and 20–40 μm galena fractions was studied. For uncleaned galena a given collector coverage produced better floatability with increasing grain size. Nitrogen had a detrimental effect only for the < 10 μm fraction, producing at a given collector coverage a recovery smaller than that obtained with air.Galena cleaned with 400 g/l ammonium acetate had very poor floatability, although xanthate abstraction was fairly high; this confirms that strong xanthate adsorption is necessary for flotation. Formation of monothiocarbonate was small in all cases, which points to a very minor influence, if any, of this compound in the flotation process.In blank flotation tests, or for very low residual xanthate concentrations, a peak at 208 nm and a shoulder at 255 nm were observed. The former was assigned to the uncomplexed Pb²⁺ ion, and the latter was tentatively attributed to the PbOH⁺ ion.Lead in solution results from dissolution of the oxidation products of galena, as galena itself has an exceedingly low solubility. The curve for total lead in solution vs. initial xanthate concentration, had a minimum for an initial xanthate concentration of 10^?5M, the further increase in dissolved lead is attributed to formation of complexes such as PbX⁺ (X = xanthate). Dissolved lead concentrations were nearly as high for cleaned as for uncleaned galena, which indicates a high oxidation rate of the mineral.     

The seismogenic thickness in Italy: constraints on potential magnitude and seismic hazard

The thickness of the seismogenic layer is a key parameter for seismic hazard, since it can be used to constrain the maximum depth of faulting and the potential magnitude. In this study, we compute the seismogenic thickness in the Italian region by defining the lower seismicity cut‐off, using high‐quality hypocentral locations of earthquakes that occurred in the past decade. Along the eastern Alps, the seismogenic thickness is about 12–14 km, laterally homogeneous along the entire south‐verging thrust front. In the Apennines extensional belt, lateral changes in seismogenic thickness are evident, and correlate with changes in the seismic energy released by past earthquakes. The potential magnitude is larger in the southern Apennines where the seismogenic thickness is greater (16–18 km) than in the northern Apennines where it is less (6–10 km) and seismic energy is partially released by the creeping of faults.