Aspects on the origin of the precursory magnetic anomalies of the Mw 6.4 Aquila earthquake

An anomalous behaviour of the scaling exponent derived from the detrended fluctuation analysis (DFA) of the time series of low frequency variations of the horizontal and vertical magnetic field components has been recently reported as being observed 2 months prior to the Mw 6.3 earthquake on 6 April 2009, close to L’Aquila city, Italy. Here, we suggest a possible physical explanation of this effect based on the experience from similar measurements in Greece. In particular, for example, we compare these observations associated with Aquila earthquake with the ones of the Mw 6.6 earthquake on 13 May 1995 at Kozani-Grevena, Greece where both magnetic field variations and seismic electric signals (SES) were recorded. Almost 1 month before the latter earthquake, anomalous variations in both electric and magnetic field were detected, the time series of that were analysed by means of DFA and led to an exponent close to unity. Similarly, the calculated DFA exponent for the Aquila earthquake time series of the anomalous magnetic field variations 2 months before the main shock was also found close to unity. These results could imply that in the case of Aquila, according to the Maxwell’s laws, one should expect to observe simultaneously with the magnetic signal an associated SES activity, provided that an appropriate station to monitoring the earth’s electric field variations in the same area was available. Hence, it seems that similar underlying non-linear dynamic processes in mechanical and as well as electromagnetic sense, with features of criticality, dominated in both pre-focal areas.     

An integrated approach for evaluating the effectiveness of landslide risk reduction in unplanned communities in the Caribbean

Despite the recognition of the need for mitigation approaches to landslide risk in developing countries, the delivery of ‘on-the-ground’ measures is rarely undertaken. With respect to other ‘natural’ hazards, it is widely reported that mitigation can pay. However, the lack of such an evidence base in relation to landslides in developing countries hinders advocacy amongst decision makers for expenditure on ex-ante measures. This research addresses these limitations directly by developing and applying an integrated risk assessment and cost–benefit analysis of physical landslide mitigation measures implemented in an unplanned community in the Eastern Caribbean. In order to quantify the level of landslide risk reduction achieved, landslide hazard and vulnerability were modelled (before and after the intervention), and project costs, direct and indirect benefits were monetised. It is shown that the probability of landslide occurrence has been substantially reduced by implementing surface-water drainage measures and that the benefits of the project outweigh the costs by a ratio of 2.7–1. This paper adds to the evidence base that ‘mitigation pays’ with respect to landslide risk in the most vulnerable communities—thus strengthening the argument for ex-ante measures. This integrated project evaluation methodology should be suitable for adoption as part of the community-based landslide mitigation project cycle, and it is hoped that this resource, and the results of this study, will stimulate further such programmes.     

SVME: an ensemble of support vector machines for detecting oil spills from full resolution MODIS images

This paper addresses oil spill detection from remotely sensed optical images. In particular, it focuses on the automatic classification of regions of interest (ROIs) in two classes, namely oil spills or look-alikes. Candidate regions and the corresponding boundaries have been manually identified from full resolution Moderate Resolution Imaging Spectroradiometer images, related to the Mediterranean Sea over the years 2008 and 2009. Then, a set of features has been extracted from each ROI, allowing to formulate the oil spill detection problem as a two-class classification task on the provided regions (i.e. using a supervised learning strategy). Since ROI classification is challenging, some desired characteristics for the classification algorithm are first identified, such as accuracy, robustness, etc. Then, a solution (called SVME) is provided: it is based on an ensemble of incremental/decremental cost-oriented Support Vector Machines, aggregated with the Receiving Operating Characteristic (ROC) convex hull method in the ROC space. Such a solution addresses all the desired characteristics. Finally, the results obtained on the collected dataset are shown. The importance of this study is the devising of a powerful classification technique that may have an impact on optical oil spill detection from space, especially if fused with satellite synthetic aperture radar data. Moreover, it is shown how the proposed system can be used as a decision support tool, to help a junior operator in making more reliable detections.     

Integrated evaluation of urban groundwater hydrogeochemistry in context of fractal behaviour of groundwater level fluctuations

The present study was carried out as part of a complex survey of urban groundwater quality and quantity in Szeged, southeast Hungary. The concentrations of 12 inorganic contaminants in 28 shallow groundwater monitoring wells were determined over a 2-year period (2010–2012). The evaluation of concentrations indicates remarkable contamination all over the city. Discriminant analysis (DA) was used to evaluate the spatial changes of groundwater quality. The groundwater levels were measured over a 14-year period (2000–2013). The fractal properties of water level fluctuations time series characterizing the groundwater system and Tisza River were investigated using rescaled range (R/S) analysis. The resulting Hurst exponents clearly showed the persistency and thus long memory effects of both the groundwater and the river flow. Comparison of the results of DA with the results of R/S analysis thus implies that the geological conditions and the changing groundwater quantities are not related to groundwater quality.

EDITOR A. Castellarin

ASSOCIATE EDITOR A. Fiori     

A conceptual hydrogeological model of ophiolitic aquifers (serpentinised peridotite): The test example of Mt. Prinzera (Northern Italy)

The main aim of this study is the experimental analysis of the hydrogeological behaviour of the Mt. Prinzera ultramafic massif in the northern Apennines, Italy. The analysed multidisciplinary database has been acquired through (a) geologic and structural survey; (b) geomorphologic survey; (c) hydrogeological monitoring; (d) physico‐chemical analyses; and (e) isotopic analyses. The ultramafic medium is made of several lithological units, tectonically overlapped. Between them, a low‐permeability, discontinuous unit has been identified. This unit behaves as an aquitard and causes a perched groundwater to temporary flow within the upper medium, close to the surface. This perched groundwater flows out along several structurally controlled depressions, and then several high‐altitude temporary springs can be observed during recharge, together with several perennial basal (i.e., low altitude) springs, caused by the compartmentalisation of the system because of high‐angle tectonic discontinuities.     

Real-time envelope cross-correlation detector: application to induced seismicity in the Insheim and Landau deep geothermal reservoirs

We develop and test a real-time envelope cross-correlation detector for use in seismic response plans to mitigate hazard of induced seismicity. The incoming seismological data are cross-correlated in real-time with a set of previously recorded master events. For robustness against small changes in the earthquake source locations or in the focal mechanisms we cross-correlate the envelopes of the seismograms rather than the seismograms themselves. Two sequenced detection conditions are implemented: After passing a single trace cross-correlation condition, a network cross-correlation is calculated taking amplitude ratios between stations into account. Besides detecting the earthquake and assigning it to the respective reservoir, real-time magnitudes are important for seismic response plans. We estimate the magnitudes of induced microseismicity using the relative amplitudes between master event and detected event. The real-time detector is implemented as a SeisComP3 module. We carry out offline and online performance tests using seismic monitoring data of the Insheim and Landau geothermal power plants (Upper Rhine Graben, Germany), also including blasts from a nearby quarry. The comparison of the automatic real-time catalogue with a manually processed catalogue shows, that with the implemented parameters events are always correctly assigned to the respective reservoir (4 km distance between reservoirs) or the quarry (8 km and 10 km distance, respectively, from the reservoirs). The real-time catalogue achieves a magnitude of completeness around 0.0. Four per cent of the events assigned to the Insheim reservoir and zero per cent of the Landau events are misdetections. All wrong detections are local tectonic events, whereas none are caused by seismic noise.     

Two GUIs-based analysis tool for spectroradiometer data pre-processing

A new graphical user interface (GUI) for pre-processing reflectance spectra, built using MATLAB and expressly designed for the ASD FieldSpec® spectroradiometer, was developed to solve problems that generally affect experimental ASD data. The GUI is characterised by an easily readable, graphic visualisation of spectra, from which the absorption band depth (ABD) can be obtained for a selected wavelength. The output format of the ASD data is a binary file with an .asd extension. The binary file, that provides a single spectrum, can be processed using a software functionality, by means of a GUI, that allows to select one or more binary files to produce a spectral library in a unique .txt file. The spectral reflectance is re-calibrated with the “convex-hull” methodology to eliminate the convex shape, which is typical of reflectance spectra. Different examples of the use of the new GUI are provided.     

Chemical and isotopic equilibrium between CO2 and CH4 in fumarolic gas discharges: Generation of CH4 in arc magmatic-hydrothermal systems

The chemical and isotopic composition of fumarolic gases emitted from Nisyros Volcano, Greece, and of a single gas sample from Vesuvio, Italy, was investigated in order to determine the origin of methane (CH₄) within two subduction-related magmatic-hydrothermal environments.Apparent temperatures derived from carbon isotope partitioning between CH₄ and CO₂ of around 340°C for Nisyros and 470°C for Vesuvio correlate well with aquifer temperatures as measured directly and/or inferred from compositional data using the H₂O-H₂-CO₂-CO-CH₄ geothermometer. Thermodynamic modeling reveals chemical equilibrium between CH₄, CO₂ and H₂O implying that carbon isotope partitioning between CO₂ and CH₄ in both systems is controlled by aquifer temperature.N₂/³He and CH₄/³He ratios of Nisyros fumarolic gases are unusually low for subduction zone gases and correspond to those of midoceanic ridge environments. Accordingly, CH₄ may have been primarily generated through the reduction of CO₂ by H₂ in the absence of any organic matter following a Fischer-Tropsch-type reaction. However, primary occurrence of minor amounts of thermogenic CH₄ and subsequent re-equilibration with co-existing CO₂ cannot be ruled out entirely. CO₂/³He ratios and δ¹³C_CO2 values imply that the evolved CO₂ either derives from a metasomatized mantle or is a mixture between two components, one outgassing from an unaltered mantle and the other released by thermal breakdown of marine carbonates. The latter may contain traces of organic matter possibly decomposing to CH₄ during thermometamorphism.     

The difficult challenge of modelling the non-linear elastic behaviour of soils within a theoretically sound framework

Hypo-elastic relations are often adopted to simulate the recoverable non-linear behaviour of soils within elasto-plastic constitutive models. In reality, they are unable to reproduce the elastic, ie, recoverable, response of materials; hence, they introduce severe inconsistencies in models based on the decomposition of the total strain tensor into its recoverable and permanent parts. Hyper-elasticity should then be used. However, existing models developed within this framework do not satisfy a number of fundamental theoretical requirements. A new hyper-elastic model is proposed, which is rigourously formulated by integrating some of the main relations which emerge from experimental results. The model satisfies all theoretical requirements and also possesses features that are fundamental for its numerical integration. The model can be considered as the correct hyper-elastic version of the classical hypo-elastic constitutive relation adopted in models based on the Critical State framework, such as the Modified Cam-Clay, with a constant Poisson's ratio.