A statistical-based approach for determining the intensity of unrest phases at Stromboli volcano (Southern Italy) using one-step-ahead forecasts of displacement time series

The evaluation of the intensity of unrest phases at active volcanoes is a crucial topic in volcano hazard studies. This is particularly troublesome in the case of persistently active volcanoes like Stromboli (Southern Italy), where intense eruptive summit activity (overflows, strong spattering, powerful explosions) has in some cases anticipated a flank eruption. In this context, a new approach for the analysis of displacement data is introduced. Daily displacements of the Stromboli crater terrace measured between January 1, 2010, and August 7, 2014, by a ground-based interferometric synthetic aperture radar system were compared, in retrospect, to displacement predictions provided by an autoregressive integrated moving average-based model. The methodology consisted in assessing when the actual displacements exceeded a fixed probability threshold for the forecasts (*95 %). Two sets of data were consequently produced: (1) series of residuals between actual displacements and model threshold (‘‘anomalies’’) and (2) series of normalized residuals between actual displacements and model threshold (‘‘normalized anomalies’’). This permitted to statistically identify and quantify the anomalous deformation at the crater terrace over the reference time interval of the analysis. Anomalies started to occur before each period of intense volcanic activity, highlighting the possibility to discern between background activity and unrest. Moreover, results indicated that the inflation of the crater terrace during the preparatory phase of the 2014 flank eruption was characterized by the greatest amount of anomalous deformation

Geophysical surveys integrated in the "Il Piano" area (Isola d'Elba, Italy) to goal census and cataloging cavities anthropic origin

Numerosi sprofondamenti si sono verificati nell’ultimo decennio in un’area di fondovalle compresa nel territorio di Rio Marina all’Isola d’Elba (località Il Piano), ed hanno interessato abitazioni, aree agricole e la strada di collegamento tra Rio Marina e Rio nell’Elba, la SP26. Nell’intorno affi ora la formazione del Calcare Cavernoso dove si è sviluppato un sistema caveale, la “Grotta di San Giuseppe”; inizialmente ciò faceva ipotizzare anche la presenza di cavità all’interno del substratocarbonatico. L’integrazione di diversi metodi geofisici indiretti ha evidenziato invece un altro motivo causale di origine antropica nella formazioni di questi sinkhole. Gli obiettivi dello studio sono stati ottenere un modello geologico e idrogeologico della zona; individuare possibili cavità e/o carenze di massa/densità che sarebbero potute evolvere in sprofondamenti; valutare la suscettibilità della zona agli sprofondamenti. Tra i risultati delle indagini geofisiche integrate: a) i modelli gravimetrici 2D e 3D hanno fornito informazioni sulla distribuzione spaziale delle densità nel sottosuolo; b) la 3D-ERT ha caratterizzato il comportamento elettrico dei materiali; c) il metodo H/V ha permesso di stimare lo spessore medio delle alluvioni. Le indagini geofisiche integrate, unite ad un’accurata ricostruzione della trasformazione ambientale dell’area, hanno consentito una caratterizzazione geomorfologica e idrogeologica del territorio. L’interpretazione di questi dati ha permesso di comprendere l’innesco dei fenomeni di sprofondamento e di redarre mappe delle aree a rischio.Published81-907A. Geofisica per il monitoraggio ambientale7SR AMBIENTE – Servizi e ricerca per la societàJCR Journa

MORFEO enters final design phase

MORFEO (Multi-conjugate adaptive Optics Relay For ELT Observations, formerly MAORY), the MCAO system for the ELT, will provide diffraction-limited optical quality to the large field camera MICADO. MORFEO has officially passed the Preliminary Design Review and it is entering the final design phase. We present the current status of the project, with a focus on the adaptive optics system aspects and expected milestones during the next project phase

A new method to identify impending failure in rock slopes

Assessing when an unstable slope is at the point of critical equilibrium is one of the main points of research and discussion in the field of rock mechanics. The topic has great relevance especially in the mining industry, as significant economic benefits derive from the ability to safely prolong works in areas where rock deformation is underway. Mining near an unstable slope requires strong confidence that a failure of the excavated area will not happen in the relatively immediate future; achieving this goal determines a more efficient and profitable extraction of the mineral resources. An effective monitoring program, able to provide notice of slope instability through the accurate and timely measurement of precursors to failure, clearly represents an essential benefit for the safety and productivity of the mine operation. Adequate anticipation of events of slope failure allows mine operators to plan and implement response actions with sufficient advance to minimize the effects of the failure on personnel safety and mine productivity. As a consequence, in most of the large surface mine operations around the world, extensive slope monitoring programs are undertaken nowadays as part of the mine performance monitoring system, by integrating various instruments such as slope stability radar, robotic total stations and geotechnical sensors. Detailed datasets of surface and underground displacements are thus collected and their analysis can provide valuable information for the understanding of the behavior of rock slopes approaching failure. Once accurate monitoring data are acquired in near-real time, the most challenging task for the site staff in charge of risk management is the set-up of suitable alarms representing when slope failure is impending. Without entering into their details, a number of “phenomenological” failure criteria (i.e. based solely on datasets of displacement measurements versus time) have been proposed in the past to forecast the time of slope failure; among these the inverse velocity method, derived from the accelerating creep theory, is the most common tool used to predict the time of failure of progressively accelerating slopes. Failure criteria often provide very useful descriptions of the risk associated with the ongoing deformation, but are also characterized by several limitations. Most notably, universal laws used to describe the displacements of failing slopes do not take into account the specific physical aspects of the phenomenon under investigation, such as the mechanical properties of the material and the influence that these have on the development of the landslide.4 With reference to the inverse velocity method another important limitation is that this assumes that velocity at failure is infinite, whereas the velocity of slopes is evidently never infinite. It follows that failure-time predictions must be regarded just as general estimations and that the inverse velocity method (and failure criteria in general) should be used with caution; the margin of error (i.e. the time difference between actual and predicted failure) can in fact range from few hours up to several days. In other cases predictions cannot be performed with adequate confidence. As a result, the issue of determining when slope failure may be impending is still of great concern. According to a different approach, other methods are instead based on the review of databases of failure case histories in order to identify characteristic conditions for slope failure occurrence. Rather than providing failure-time predictions, the aim is to define recurrent correlations between certain variables in close proximity to the instant of failure. In the framework of the ACARP (Australian Coal Association Research Program) C17023 project, Cabrejo and Harries analyzed a large database of deformation data acquired by Slope Stability Radar (SSR) devices in several undisclosed Australian open-cut coal mines and reviewed 78 case histories of mine slope failure, which were all anticipated by progressive accelerations. Parameters associated to both displacement and velocity at different stages of the failure process were considered by the authors, but reliable mathematical expressions able to comprehensively characterize the observed events could not be found. In this work further in-depth analysis of this database is presented. In particular, the average accelerations during different sub-sets of time prior to the instant of failure have been studied and highlighted the presence of a common behavior of the slope failures in the database

A simple method to help determine landslide susceptibility from spaceborne InSAR data: the Montescaglioso case study

On December 3, 2013, a large complex landslide was triggered SW of the town of Montescaglioso (Southern Italy), causing the destruction of roads, commercial buildings and private dwellings, as well as several direct and indirect economic losses. A set of interferometric ground measurements acquired by the Cosmo-SkyMed satellite constellation and processed by means of the SqueeSAR algorithm was used to study the pre-event slope displacements in the entire Montescaglioso municipal area. Data span from January 30, 2012, to December 2, 2013, and show average line-of-sight velocities of 1–10 mm/year in the slope sector ultimately affected by the collapse. In retrospect, a time series analysis of the radar targets was performed in order to identify and characterize all the slope instabilities in proximity of the town. This was based on the setup of characteristic thresholds of displacement. The procedure permitted to locate several areas which recurrently exceeded these previously established thresholds, in consistency with the amount of precipitation. In particular, the major source of potential hazard in the area was indeed found where the December 3, 2013, landslide eventually occurred. The results of this quick data processing technique were validated through comparison with two independently developed landslide maps. This simple method, which is not supposed to diminish the importance of geomorphologic field surveys, could improve both the accuracy and the update rate of landslide susceptibility maps. Not relying on arbitrary or empirically derived approaches, it has the advantage of computing statistically based thresholds specific for each time series. By indicating the slope sectors in higher need of deeper in situ investigation, more support could be provided to administrative bodies for the processes of risk assessment and management

On the monitoring and early-warning of brittle slope failures in hard rock masses: Examples from an open-pit mine

The management of unstable slopes is one of the most critical issues when dealing with safety in open-pit mines. Suitable notice of impending failure events must be provided, and at the same time the number of false alarms must be kept to a minimum to avoid financial losses deriving from unnecessary outages of the production works. Comprehensive slope monitoring programs and early warning systems are usually implemented to this aim. However, systematic procedures for their tuning are lacking and several key factors are often overlooked. Therefore the mitigation of slope failure risk is still a topic of great concern, especially in open-pit mines excavated through hard rock masses featuring markedly brittle behavior, which supposedly provide little or no measurable precursors to failure. In this paper, 9 instabilities occurred at an undisclosed open-pit mine, and monitored by ground-based radar devices, were reviewed with the goal of characterizing the typical slope deformation behavior and defining the appropriate strategy for the setup of alarms. The estimated mass of the case studies ranged from 1500 t to 750,000 t. 5 instabilities culminated to failure, whereas the other 4, although showing considerable amounts and rates of movement, ultimately did not fail. The analysis provided critical insights into the deformation of hard rock masses of high geomechanical quality, and allowed the identification of â\u80\u9csignatureâ\u80\u9d parameters of the failure events. General operative recommendations for effective slope monitoring and early warning were consequently derived

Displacement of a landslide retaining wall and application of an enhanced failure forecasting approach

The 10-mile Slide is contained within an ancient earthflow located in British Columbia, Canada. The landslide has been moving slowly for over 40 years, requiring regular maintenance work along where a highway and a railway track cross the sliding mass. Since 2013, the landslide has shown signs of retrogression. Monitoring prisms were installed on a retaining wall immediately downslope from the railway alignment to monitor the evolution of the retrogression. As of September 2016, cumulative displacements in the horizontal direction approached 4.5 m in the central section of the railway retaining wall. After an initial phase of acceleration, horizontal velocities showed a steadier trend between 3 and 9 mm/day, which was then followed by a second acceleration phase. This paper presents an analysis of the characteristics of the surface displacement vectors measured at the monitoring prisms. Critical insight on the behavior and kinematics of the 10-mile Slide retrogression was gained. An advanced analysis of the trends of inverse velocity plots was also performed to assess the potential for a slope collapse at the 10-mile Slide and to obtain further knowledge on the nature of the sliding surface