Giovanni Gigli

The ground-based InSAR monitoring system at Stromboli volcano: linking changes in displacement rate and intensity of persistent volcanic activity

Stromboli volcano (Aeolian Archipelago, Southern Italy) experienced an increase in its volcanic activity from late December 2012 to March 2013, when it produced several lava overflows, major Strombolian explosions, crater-wall collapses pyroclastic density currents and intense spatter activity. An analysis of the displacement of the NE portion of the summit crater terrace and the unstable NW flank of the volcano (Sciara del Fuoco depression) has been performed with a ground-based interferometric synthetic aperture radar (GBInSAR) by dividing the monitored part of the volcano into five sectors, three in the summit vents region and two in the Sciara del Fuoco. Changes in the displacement rate were observed in sectors 2 and 3. Field and thermal surveys revealed the presence of an alignment of fumaroles confirming the existence of an area of structural discontinuity between sectors 2 and 3. High displacement rates in sector 2 are interpreted to indicate the increase in the magmastatic pressure within the shallow plumbing systems, related to the rise of the magma level within the conduits, while increased displacement rates in sector 3 are connected to the lateral expansion of the shallow plumbing system. The increases and decreases in the displacement rate registered by the GBInSAR system in the upper part of the volcano have been used as a proxy for changes in the pressure conditions in the shallow plumbing system of Stromboli volcano and hence to forecast the occurrence of phases of higher-intensity volcanic activity.

Landslide inventory map for the Briga and the Giampilieri catchments, NE Sicily, Italy

On 1 October 2009, a high intensity storm hit the Ionian coast of Sicily, SW of Messina, Italy. The Santo Stefano di Briga rain gauge, located 2 km W of the Ionian coast, recorded 225 mm of rain in seven hours. The intense rainfall event triggered abundant slope failures, and resulted in widespread erosion and deposition of debris along ephemeral drainage channels, extensive inundation, and local modifications of the coastline. Landslides occurred in a territory prone to slope failures, due to the local geological and geomorphological settings. Many landslides were related to the presence of roads lacking adequate drainage. Abandoned terraced slopes lacking proper drainage, and unmaintained dry walls were also related to slope failures. Damage was particularly severe in small villages and at several sites along the transportation network. The shallow landslides and the inundation resulted in 37 fatalities, including 31 deaths and six missing persons, and innumerable injured people. After the event, an accurate landslide inventory map was prepared for the Briga and the Giampilieri catchments. The map shows: (i) the distribution of the event landslides triggered by the 1 October 2009 rainfall event; (ii) the distribution of the pre-existing slope failures; and (iii) other geomorphological features related to fluvial processes and slope movements. The landslide inventory map was prepared at 1:10,000 scale through a combination of field surveys and photo-interpretation of pre-event and post-event, stereoscopic and pseudo-stereoscopic, aerial photography. Different types of aerial photographs were analysed visually to prepare the landslide inventory map. The event landslides were mapped through the interpretation of pseudo-stereoscopic colour photographs taken shortly after the event at 1:3500 scale, combined with digital stereoscopic photographs at approximately 1:4500 scale, taken in November 2009. The pre-event landslides and the associated geomorphological features were mapped using 1:33,000 scale aerial photographs flown in 1954, 1955, and 2005. The event and pre-existing landslides were checked in the field in the period October–November 2009.

Exploitation of Amplitude and Phase of Satellite SAR Images for Landslide Mapping: The Case of Montescaglioso (South Italy)

Pre- event and event landslide deformations have been detected and measured for the landslide that occurred on 3 December 2013 on the south-western slope of the Montescaglioso village (Basilicata Region, southern Italy). In this paper, ground displacements have been mapped through an integrated analysis based on a series of high resolution SAR (Synthetic Aperture Radar) images acquired by the Italian constellation of satellites COSMO-SkyMed. Analysis has been performed by exploiting both phase (through multi-image SAR interferometry) and amplitude information (through speckle tracking techniques) of the satellite images. SAR Interferometry, applied to images taken before the event, revealed a general pre-event movement, in the order of a few mm/yr, in the south-western slope of the Montescaglioso village. Highest pre-event velocities, ranging between 8 and 12 mm/yr, have been recorded in the sector of the slope where the first movement of the landslide took place. Speckle tracking, applied to images acquired before and after the event, allowed the retrieval of the 3D deformation field produced by the landslide. It also showed that ground displacements produced by the landslide have a dominant SSW component, with values exceeding 10 m for large sectors of the landslide area, with local peaks of 20 m in its central and deposit areas. Two minor landslides with a dominant SSE direction, which were detected in the upper parts of the slope, likely also occurred as secondary phenomena as consequence of the SSW movement of the main Montescaglioso landslide.

3-D geomechanical rock mass characterization for the evaluation of rockslide susceptibility scenarios

An integrated methodology based on traditional field and remote surveys such as terrestrial laser scanning and terrestrial infrared thermography is proposed, with the aim of defining susceptibility scenarios connected to rock slopes affected by instability processes. The proposed methodology was applied to a rock slope threatening a coastal panoramic roadway located in western Elba Island (Livorno district, central Italy). The final aim of the methodology was to obtain an accurate three-dimensional rock mass characterization in order to detect the potentially more hazardous rock mass portions, calculate their volume, and collect all the required geomechanical and geometrical parameters to perform a detailed stability analysis. The proposed approach proved to be an effective tool in the field of engineering geology and emergency management, when it is often urgently necessary to minimize survey time when operating in dangerous environments and gather all the required information as fast as possible.

Guidelines on the use of inverse velocity method as a tool for setting alarm thresholds and forecasting landslides and structure collapses

Predicting the time of failure is a topic of major concern in the field of geological risk management. Several approaches, based on the analysis of displacement monitoring data, have been proposed in recent years to deal with the issue. Among these, the inverse velocity method surely demonstrated its effectiveness in anticipating the time of collapse of rock slopes displaying accelerating trends of deformation rate. However, inferring suitable linear trend lines and deducing reliable failure predictions from inverse velocity plots are processes that may be hampered by the noise present in the measurements; data smoothing is therefore a very important phase of inverse velocity analyses. In this study, different filters are tested on velocity time series from four case studies of geomechanical failure in order to improve, in retrospect, the reliability of failure predictions: Specifically, three major landslides and the collapse of an historical city wall in Italy have been examined. The effects of noise on the interpretation of inverse velocity graphs are also assessed. General guidelines to conveniently perform data smoothing, in relation to the specific characteristics of the acceleration phase, are deduced. Finally, with the aim of improving the practical use of the method and supporting the definition of emergency response plans, some standard procedures to automatically setup failure alarm levels are proposed. The thresholds which separate the alarm levels would be established without needing a long period of neither reference historical data nor calibration on past failure events.

Combined Finite-Discrete Numerical Modeling of Runout of the Torgiovannetto di Assisi Rockslide in Central Italy

AbstractThe combined finite–discrete-element method (FDEM) is an advanced and relatively new numerical modeling technique that combines the features of the FEM with those of the discrete-element method. It simulates the transition of brittle geomaterials from continua to discontinua through fracture growth, coalescence, and propagation. With FDEM, it is possible to simulate landslides from triggering to runout and carry out landslide scenario analyses, the results of which can be successively adopted for cost-effective early warning systems. The purpose of this paper is to describe the results of the FDEM simulations of the triggering mechanism and the evolution scenarios of the Torgiovannetto di Assisi rockslide (central Italy), a depleted limestone quarry face where a rock wedge with an approximate volume of 182,000 m3 lies in limit equilibrium conditions, posing relevant issues in terms of civil protection. The results obtained demonstrate that the FDEM is able to realistically simulate the different p...

Landslide hazard, monitoring and conservation strategy for the safeguard of Vardzia Byzantine monastery complex, Georgia

This paper reports preliminary results of a feasibility project developed in cooperation with National Agency for Cultural Heritage Preservation of Georgia, and aimed at envisaging the stability conditions of the Vardzia monastery slope (rupestrian city cave in the south-western Georgia). The aim is the implementation of a low-impact monitoring system together with long-term mitigation/conservation policies. A field analysis was conducted to reconstruct geometry of the rocky cliff, characteristics of discontinuities, main failure modes, and volume of potential unstable blocks and geomechanical parameters. Instability processes are the combination of causative factors such as the following: lithology, frequency and orientation of discontinuities, slope orientation, physical and mechanical characteristics of slope-forming materials, and morphological and hydrological boundary conditions. The combined adoption of different survey techniques (e.g., 3D laser scanner, ground-based radar interferometry) could be the best solution in the interdisciplinary field of cultural heritage preservation policies. The collected data will be the basis for future activities to be completed in collaboration with local authorities for a complete hazard and risk characterization for the monastery site and the development of an early warning system to allow safe exploitation for touristic activities and for historical site preservation.

A new appraisal of the Ancona landslide based on geotechnical investigations and stability modelling

On the night of 13 December 1982, Ancona experienced the catastrophic reactivation of an old and large landslide located along the coast to the west of the city. The outcomes of past and new geotechnical investigations and the data from the 30 year readings of the monitoring instruments have been integrated to redefine and update the actual location of the sliding surfaces. According to the new analysis, the landslide involves four main sliding surfaces with different extents and depths. The deepest surfaces converge at depth in a shear band and their toes are positioned near or beyond the coast. Numerical and analytical modelling of the landslide has been carried out using the newly derived sliding surface geometries. The numerical modelling has allowed a qualitative assessment of the deformation pattern, confirming the geometry of the sliding surfaces derived from the geotechnical investigations. The stability analyses have been performed applying the limit equilibrium method to quantify the instability conditions of the landside. The analyses have been carried out for five stratigraphic–geotechnical scenarios. All of these scenarios show a stability condition near the limit equilibrium.

Event scenario analysis for the design of rockslide countermeasures

The Torgiovannetto quarry (Assisi municipality, central Italy) is an example of a site where the natural equilibrium was altered by human activity, causing current slope instability phenomena which threaten two roadways important for the local transportation. The quarry front, having a height of about 140 m, is affected by a 182,000 m3 rockslide developed in intensely fractured limestone and is too large to be stabilized. In 2003 some tension cracks were detected in the vegetated area above the quarry upper sector. From then on, several monitoring campaigns were carried out by means of different instrumentations (topographic total station, extensometers, inclinometers, ground-based interferometric radar, laser scanner and infrared thermal camera), allowing researchers to accurately define the landslide area and volume. The latter’s major displacements are localized in the eastern sector. The deformational field appears to be related to the seasonal rainfall. The landslide hazard associated with the worst case scenario was evaluated in terms of magnitude, intensity and triggering mechanism. For the definition of the possible runout process the DAN 3D code was employed. The simulation results were used in order to design and construct a retaining embankment. Furthermore, in order to preserve both the safety of the personnel involved in its realization and of the roadways users, an early warning system was implemented. The early warning system is based on daily-averaged displacement velocity thresholds. The alarm level is reached if the prediction based on the methods of Saito (1969) and Fukuzono (1985) forecasts an imminent rupture.

Monitoring the rapid-moving reactivation of earth flows by means of GB-InSAR: The April 2013 Capriglio Landslide (Northern Appennines, Italy)

This paper presents the main results of the GB-InSAR (ground based interferometric synthetic aperture radar) monitoring of the Capriglio landslide (Northern Apennines, Emilia Romagna Region, Italy), activated on 6 April 2013. The landslide, triggered by prolonged rainfall, is constituted by two main adjacent enlarging bodies with a roto-translational kinematics. They activated in sequence and subsequently joined into a large earth flow, channelizing downstream of the Bardea Creek, for a total length of about 3600 m. The displacement rate of this combined mass was quite high, so that the landslide toe evolved with velocities of several tens of meters per day (with peaks of 70–80 m/day) in the first month, and of several meters per day (with peaks of 13–14 m/day) from early May to mid-July 2013. In the crown area, the landslide completely destroyed a 450 m sector of provincial roadway S.P. 101, and its retrogression tendency exposed the villages of Capriglio and Pianestolla, located in the upper watershed area of the Bardea Creek, to great danger. Furthermore, the advancing toe seriously threatened the Antria bridge, representing the “Massese” provincial roadway S.P. 665R transect over the Bardea Creek, the only strategic roadway left able to connect the above-mentioned villages. With the final aim of supporting local authorities in the hazard assessment and risk management during the emergency phase, on 4 May 2013 aerial optical surveys were conducted to accurately map the landslide extension and evolution. Moreover, a GB-InSAR monitoring campaign was started in order to assess displacements of the whole landslide area. The versatility and flexibility of the GB-InSAR sensors allowed acquiring data with two different configurations, designed and set up to continuously retrieve information on the landslide movement rates (both in its upper slow-moving sectors and in its fast-moving toe). The first acquisition mode revealed that the Capriglio and Pianestolla villages were affected by minor displacements (at an order of magnitude of a few millimeters per month). The second acquisition mode allowed to acquire data every 28 seconds, reaching very high temporal resolution values by applying the GB-InSAR technique.