Forward logistic regression for earth-flow landslide susceptibility assessment in the Platani river basin (southern Sicily,Italy)

Forward logistic regression has allowed us to derive an earth-flow susceptibility model for the Tumarrano river basin, which was defined by modeling the statistical relationships between an archive of 760 events and a set of 20 predictors. For each landslide in the inventory, a landslide identification point (LIP) was automatically produced as corresponding to the highest point along the boundary of the landslide polygons, and unstable conditions were assigned to cells at a distance up to 8 m. An equal number of stable cells (out of landslides) was then randomly extracted and appended to the LIPs to prepare the dataset for logistic regression. A model building strategy was applied to enlarge the area included in training the model and to verify the sensitivity of the regressed models with respect to the locations of the selected stable cells. A suite of 16 models was prepared by randomly extracting different unoverlapping stable cell subsets that have been appended to the unstable ones. Models were finally submitted to forward logistic regression and validated. The results showed satisfying and stable error rates (0.236 on average, with a standard deviation of 0.007) and areas under the receiver operating characteristic (ROC) curve (AUCs) (0.839 for training and 0.817 for test datasets) as well as factor selections (ranks and coefficients). As regards the predictors, steepness and large-profile and local-plan topographic curvatures were systematically selected. Clayey outcropping lithology, midslope drainage, local and midslope ridges, and canyon landforms were also very frequently (from eight to 15 times) included in the models by the forward selection procedures. The model-building strategy allowed us to produce a performing earth-flow susceptibility model, whose model fitting, prediction skill, and robustness were estimated on the basis of validation procedures, demonstrating the independence of the regressed model on the specific selection of the stable cells.     

Morphodynamics and sedimentary structures of bedforms under supercritical‐flow conditions: New insights from flume experiments

Supercritical‐flow phenomena are fairly common in modern sedimentary environments, yet their recognition and analysis remain difficult in the stratigraphic record. This fact is commonly ascribed to the poor preservation potential of deposits from high‐energy supercritical flows. However, the number of flume data sets on supercritical‐flow dynamics and sedimentary structures is very limited in comparison with available data for subcritical flows, which hampers the recognition and interpretation of such deposits. The results of systematic flume experiments spanning a broad range of supercritical‐flow bedforms (antidunes, chutes‐and‐pools and cyclic steps) developed in mobile sand beds of variable grain sizes are presented. Flow character and related bedform patterns are constrained through time‐series measurements of bed configurations, flow depths, flow velocities and Froude numbers. The results allow the refinement and extension of some widely used bedform stability diagrams in the supercritical‐flow domain, clarifying in particular the morphodynamic relations between antidunes and cyclic steps. The onset of antidunes is controlled by flows exceeding a threshold Froude number. The transition from antidunes to cyclic steps in fine to medium‐grained sand occurs at a threshold mobility parameter. Sedimentary structures associated with supercritical bedforms developed under variable aggradation rates are revealed by means of combining flume results and synthetic stratigraphy. The sedimentary structures are compared with examples from field and other flume studies. Aggradation rate is seen to exert an important control on the geometry of supercritical‐flow structures and should be considered when identifying supercritical bedforms in the sedimentary record.     

Using beryllium-7 to evaluate soil erosion processes in agricultural lands in semiarid regions of Central Argentina

This work presents the results of a soil erosion study using the ⁷Be technique. This technique estimates the water erosion/deposition from the comparison between ⁷Be soil content of a reference site and an eroded or sedimented site. The soil samples were collected from an agricultural area of the semiarid region of Argentina near San Luis City, which has a marked rainfall season. The area has been used for crop cultivation, being subjected to plowing practices. The ⁷Be in the Reference Site was in the first centimeter of soil, showing the typical exponential decreasing of ⁷Be soil content with depth, with the ⁷Be inventories value being 340?±?50 Bq m^?2 for the dry season and 571?±?48 Bq m^?2 for the rainy season. The ⁷Be technique was applied to a potential eroded site subjected to traditional tillage practices (plowing). A net soil erosion value of 13.5 t ha^?1 (1.35 kg m^?2) was obtained. From the assumptions of the applied technique, we can draw the inference that this erosion was caused by rains produced in the month prior to the date of soil sampling.     

Quantitative analysis of consequences to masonry buildings interacting with slow-moving landslide mechanisms: a case study

Quantitative analysis of consequences (in terms of expected monetary losses) induced by slow-moving landslide mechanisms to buildings or infrastructure networks is a key step in the landslide risk management framework. It can influence risk mitigation policies as well as help authorities in charge of land management in addressing/prioritizing interventions or restoration works. This kind of analysis generally requires multidisciplinary approaches, which cannot disregard a thorough knowledge of landslide mechanisms, and rich datasets that are seldom available as testified by the limited number of examples in the scientific literature. With reference to the well-documented case study of Lungro town (Calabria region, southern Italy)—severely affected by slow-moving landslides of different types—the present paper proposes and implements a multi-step procedure for monetary loss forecasting associated with different landslide kinematic/damage scenarios. Procedures to typify landslide mechanisms and physical vulnerability analysis, previously tested in the same area, are here appropriately merged to derive both kinematic and damage scenarios to the exposed buildings. Then, the outcomes are combined with economic data in order to forecast monetary loss at municipal scale. The proposed method and the obtained results, once further validated, could stand as reference case for other urban areas in similar geo-environmental contexts in order to derive useful information on expected direct consequences unless slow-moving landslide risk mitigation measures are taken.     

A study on the effects of seismicity on subsidence in foreland basins: An application to the Venice area

Foreland basins are flat elongated areas occurring along subduction and collision zones worldwide. We show that, in such basins, subsidence can be induced by earthquakes generated along bordering thrust faults due to coseismic displacement, postseismic displacement and liquefaction-induced compaction.As an example, the potential effects of earthquakes on the subsidence of Venice, which is located in the Po Plain foreland basin, are discussed. It is generally assumed that natural subsidence of Venice is continuous and that subsidence rates are rather constant through time. However, catastrophic pulses of subsidence cannot be ruled out as taught by the sudden disappearance of the island of Malamocco at the beginning of the XII century.The results of numerical models specifically run suggest that the risk of subsidence accelerations in Venice due to coseismic displacements is negligible. Modelling results from literature suggest that postseismic subsidence could be of the order of 1 cm. Although the effects of a single event should be improbably detectable, such a subsidence is not a priori negligible considering the number of seismogenic sources located within 100 km from the town.Historical sources are utilized to discuss the feasibility of liquefaction-induced subsidence in Venice. It is shown that the destruction and sinking of ancient Malamocco is roughly coincident with a strong earthquake cycle that was associated to phenomena that can be explained with liquefaction of sandy layers. Although the historical documents do not permit to establish a clear causal link between the earthquake and land subsidence, it is concluded that liquefaction-induced subsidence cannot be ruled out as a potential source for local subsidence acceleration.     

A population of high-redshift type 2 quasars – I. Selection criteria and optical spectra

We discuss the relative merits of mid-infrared and X-ray selection of type 2 quasars. We describe the mid-infrared, near-infrared and radio selection criteria used to find a population of redshift   z ∼ 2  type 2 quasars which we previously argued suggests that most supermassive black hole growth in the Universe is obscured. We present the optical spectra obtained from the William Herschel Telescope, and we compare the narrow emission-line luminosity, radio luminosity and maximum size of jets to those of objects from radio-selected samples. This analysis suggests that these are genuine radio-quiet type 2 quasars, albeit the radio-bright end of this population. We also discuss the possibility of two different types of quasar obscuration, which could explain how the ∼2–3:1 ratio of type 2 to type 1 quasars preferred by modelling our population can be reconciled with the ∼1:1 ratio predicted by unified schemes.     

The Mid-Carboniferous to Lowermost Permian succession of Spiti (Po Group and Ganmachidam Formation; Tethys Himalaya,Northern India): Gondwana glaciation and rifting of Neo-Tethys.

Abstract

The upper Lower Carboniferous to lowermost Permian terrigenous succession of the Spiti Valley can be subdivided into five formations (Thabo Formation, Fenestella Shale, Kabjima Quartzarenite, Chichong Formation and Ganmachidam Diamictite), here described in detail and subdivided into members or lithozones.

The Po Group, overlying the platform carbonates and gypsum deposits of the Lipak Formation, records an increase of subarkosic to quartzarenitic terrigenous detritus derived from uplift and erosion of continental blocks in the south during the initial stage of Neo-Tethyan rifting. Increasing mineralogic stability through the Thabo Formation broadly coincides with a climate change from tropical arid to temperate humid conditions during the Visean-Serpukhovian. The Fenestella Shale, containing rich brachiopod associations of Bashkirian age, documents a stage of widespread subsidence and transgression, followed by the regressive Kabjima Quartzarenite, which records recycling of quartzose sedimentary sequences in the south.

The Chichong Formation marks another transgressive event, associated with a significant increase of granitoid detritus, partly from nearby Lesser to High Himalayan source areas. Chaetetid, cephalopod and brachiopod faunas hint at a Moscovian age for the “Chaetetid beds”, at the top of which varve-like lamination and scattered pebbles suggest glacially influenced deposition. The overlying glacio-fluvial (?) cobble conglomerates (“Pebbly beds”) reflect onset of rapid tectonic uplift.

Abundant detritus from sedimentary rocks characterizes the overlying Ganmachidam Diamictite, deposited in glacio-marine environments; cold-water marine faunas of Asselian age occur in its middle part. Erosion of progressively older pre-rift sedimentary successions is ascribed to basin inversion, associated with unroofing of anatectic granitoids of the Lesser and High Himalayas. Basaltic to rhyolitic volcanic detritus documents alkalic magmatism at the climax of continental rifting.     

A geometrical method for quantifying endmembers' fractions in three-component groundwater mixing

We present a new geometrical method capable of quantifying and illustrating the outcomes of a three-component mixing dynamics. In a three-component mixing scenario, classical algebraic equations and endmember mixing analysis (EMMA) can be used to quantify the contributions from each fraction. Three-component mixing of natural waters, either in an element–element plot or by using the EMMA mixing subspace is described by a triangular shaped distribution of sample points where each endmember is placed on an apex, while each side corresponds to the mixing function of the two endmembers placed at the apex, considering the third endmembers' contribution equal to zero. Along each side, the theoretical mixing fractions can be computed using mass balance equations. Samples with contributions from three endmembers will plot inside the triangle, while the homogeneous barycentric coordinate projections can be projected onto the three sides. The geochemistry observed in the mineralized Ferrarelle aquifer system (southern Italy) results from three-component mixing of groundwater, each with diagnostic geochemical compositions. The defined boundary conditions allow us to parameterize and validate the procedures for modelling mixing, including selection of suitable geochemical tracers.     

Copper emissions from antifouling paint on recreational vessels

Trace metals, especially copper, are commonly occurring contaminants in harbors and marinas. One source of copper to these environs is copper-based antifouling coatings used on vessel hulls. The objective of this study was to measure dissolved copper contributions from recreational vessel antifouling coatings for both passive leaching and hull cleaning activities. To accomplish this goal, three coating formulations, including hard vinyl, modified epoxy and a biocide free bottom paint were applied on fiberglass panels and placed in a harbor environment. In situ measurements of passive leaching were made using a recirculating dome system. Monthly average flux rates of dissolved copper for the hard vinyl and modified epoxy coatings were 3.7 and 4.3 microg/cm(2)/day, respectively, while flux rates for the biocide free coating was 0.2 microg/cm(2)/day. The highest passive flux rates were measured initially after cleaning activities, rapidly decreasing to a baseline rate within three days, regardless of copper-based coating formulation. Hull cleaning activities generated between 8.6 and 3.8 microg dissolved copper/cm(2)/event for the modified epoxy and hard vinyl coatings, respectively. Aggressive cleaning using an abrasive product doubled the copper emissions from the modified epoxy coating, but produced virtually no change in the much tougher hard vinyl coating. When compared on a mass basis, roughly 95% of copper is emitted during passive leaching compared to hull cleaning activities over a monthly time period for a typical 9.1 m power boat.