Daniela Piacentini

Late Quaternary episodic displacement on a sackung scarp in the central Spanish Pyrenees. Secondary paleoseismic evidence

A sackung scarp has been investigated by trenching in the central Spanish Pyrenees. This feature is located 18 km to the SW of the North Maladeta Fault, which is the most probable source of the Mw 5.3 Vielha earthquake of 1923. Three displacement events have been inferred for the trenched sackung based on colluvial wedge stratigraphy and fault truncation. The increasing amount of deformation in each successive faulting event may be related to the progressive weakening of the slope through time. A minimum vertical slip rate of 0.19 mm/yr has been calculated for the sackung scarp. Several arguments suggest that the episodic displacement of the analysed sackung is controlled by strong seismic shaking: (a) Spatial association of the sackung features with the North Maladeta Fault; (b) Episodic displacement with a millennial recurrence (5.6 kyr) consistent with the expectable earthquake recurrence interval for a low slip rate fault, like the neighbouring North Maladeta Fault. Demonstrating in future investigations that the sackung features in the area constitute archives of large paleoearthquakes would be of great interest for seismic hazard assessments. They might help to improve the catalogue of paleoearthquakes and might provide information on earthquake recurrence intervals and the age of the most recent event (MRE).

A multidisciplinary approach for rock spreading and block sliding investigation in the north-western coast of Malta

Landslides are widespread along the north-western coast of the Island of Malta and are strictly linked to the structural setting. Exemplary cases of rock spreading and block sliding phenomena characterise this stretch of coast. They are favoured by the overposition of two different geological units widely outcropping there, the Blue Clay Formation and the Upper Coralline Limestone Formation. The latter forms a wide plateau, bordered by vertical cliffs. At the foot of the cliffs, clayey terrains crop out and develop gentle slopes covered by large blocks detached and moved by rock spreading and block sliding phenomena. These mass movements are favoured by the fragile behaviour of limestones, which cap clays, otherwise characterised by visco-plastic properties. In order to investigate the kinematics and the evolution of these types of coastal landslides, a multidisciplinary and multitechnical approach was applied on a study site, named Il-Prajjet, which provides a spectacular case of rock spreading evolving into block sliding. This paper illustrates the results achieved by means of different engineering geological and geophysical techniques allied with traditional detailed geomorphological survey and mapping. In particular, the surface displacements of the landslides were determined using long-term GPS observations, acquired approximately every 6 months, over a 4.5-year period. A network of GPS benchmarks were distributed on the edge of a limestone plateau affected by rock spreading and on a series of displaced blocks making up a large block slide, finally enabling the definition of the state of activity and the rates of movement to be performed. In addition, the results deriving from two continuous fissurimeters more recently installed at the edge of two persistent joints over the block sliding area are outlined, with reference to the correlation between variations of crack apertures and precipitation input. In order to identify main structural discontinuities and to reconstruct variability of underground surface contact between clays and overlying limestones, Resistivity Tomography profiles and GPR investigations were carried out. Finally, the results obtained by combining the outputs of geophysical surveys and different field monitoring activities can be considered a first step on which numerical models can be developed and validated, in order to assess landslide hazard and risk of this stretch of Maltese coastline.

Geomorphological map of the NW Coast of the Island of Malta (Mediterranean Sea)

This paper presents the results of geomorphological investigations carried along the north-western coast of the Island of Malta. Field surveys, accompanied by aerial photo-interpretation, have led to the production of a geomorphological map at 1:7500 scale which outlines the main processes and related landforms. The latter are the result of the complex interplay of structural, gravitational, coastal and karst processes. Particular attention was devoted to the recognition, identification and mapping of landslides which affect large coastal sectors of the study area, locally giving rise to hazardous conditions.

Landslide susceptibility modeling assisted by Persistent Scatterers Interferometry (PSI): an example from the northwestern coast of Malta

Abstract Persistent Scatterers Interferometry (PSI) techniques are widely employed in geosciences to detect and monitor landslides with high accuracy over large areas, but they also suffer from physical and technological constraints that restrict their field of application. These limitations prevent us from collecting information from several critical areas within the investigated region. In this paper, we present a novel approach that exploits the results of PSI analysis for the implementation of a statistical model for landslide susceptibility. The attempt is to identify active mass movements by means of PSI and to avoid, as input data, time-/cost-consuming and seldom updated landslide inventories. The study has been performed along the northwestern coast of Malta (central Mediterranean Sea), where the peculiar geological and geomorphological settings favor the occurrence of a series of extensive slow-moving landslides. Most of these consist in rock spreads, evolving into block slides, with large limestone blocks characterized by scarce vegetation and proper inclination, which represent suitable natural radar reflectors for applying PSI. Based on geomorphometric analyses and geomorphological investigations, a series of landslide predisposing factors were selected and a susceptibility map created. The result was validated by means of cross-validation technique, field surveys and global navigation satellite system in situ monitoring activities. The final outcome shows a good reliability and could represent an adequate response to the increasing demand for effective and low-cost tools for landslide susceptibility assessment.

Landslides Along the North-West Coast of the Island of Malta

The paper shows the results of geomorphological and engineering-geological investigations carried out along the north-western coast of the Island of Malta, with special emphasis on landslides. Field surveys and aerial-photo interpretation allowed the recognition, identification and mapping of a series of landslides of different type and size, some of which showing evidence of activity. Coastal instability in the studied area is deeply controlled by structural factors, such as tectonic and stratigraphic ones. The research envisaged a multidisciplinary approach, which also included landslide monitoring in specific sites which were selected for detailed investigations, owing to the peculiarity of the instability processes occurring and for the related hazard and risk conditions. The paper outlines the research phases and the results achieved which proved to be fruitful thanks to the application of different methodologies for the study of coastal landslides. Particular attention has been paid to rock spreading phenomena, which are widespread along the north-western coast of Malta due to the superimposition of limestones over clayey terrains.

Advanced SAR Interferometric Analysis to Support Geomorphological Interpretation of Slow-Moving Coastal Landslides (Malta, Mediterranean Sea)

An advanced SAR interferometric analysis has been combined with a methodology for the automatic classification of radar reflectors phase histories to interpret slope-failure kinematics and trend of displacements of slow-moving landslides. To accomplish this goal, the large dataset of radar images, acquired in more than 20 years by the two European Space Agency (ESA) missions ERS-1/2 and ENVISAT, was exploited. The analysis was performed over the northern sector of Island of Malta (central Mediterranean Sea), where extensive landslides occur. The study was assisted by field surveys and with the analysis of existing thematic maps and landslide inventories. The outcomes allowed definition of a model capable of describing the geomorphological evolution of slow-moving landslides, providing a key for interpreting such phenomena that, due to their slowness, are usually scarcely investigated.

Coastline at Risk: Methods for Multi-Hazard Assessment

ABSTRACT SOLDATI, M., MAQUAIRE, O., ZEZERE, J. L., PIACENTINI, D and LISSAK, C, 2011. Coastline at Risk: Methods for Multi-Hazard Assessment. In: Micallef, A. (ed.), MCRR3–2010 Conference Proceedings, Journal of Coastal Research, Special Issue, No. 61, pp. 335–339. Grosseto, Tuscany, Italy, ISSN 0749-0208. In recent years the interest for coastal hazards has increased significantly due to extreme events, sometimes related to climate change, that frequently occur in different parts of the world, often inducing high risk situations. This paper outlines the objectives, perspectives and preliminary results of a research project entitled “Coastline at risk: Methods for multi-hazard assessment” which aims at providing useful knowledge for the mitigation of coastal instability. The project is managed by the European Centre on Geomorphological Hazards (Centre Européen sur les Risques Geomorphologiques, CERG) and funded by the EUR-OPA Major Hazards Agreement. Investigations are focused on coastal landslides in three different morpho-climatic European environments: Malta (Mediterranean coastline), Lower Normandy (Channel coastline) and Central Portugal (Atlantic coastline). The research outputs are expected to provide a significant opportunity for scientific discussion based on the comparison of data regarding instability situations in the context of multi-hazards assessment. The latter has until now dealt slightly with the coasts of Malta, Normandy and Portugal on which the investigations will be focused, despite significant risk issues present there, as evidenced from a series of accidents and damages recorded after landslide events. The aims of the project will be pursued through multidisciplinary investigations which foresee geomorphological and engineering-geological approaches. Integrated avant-garde research techniques, both traditional and innovative, will be applied with special reference to mapping, monitoring and modelling of coastal instability phenomena. The final objective is to propose a method for coastal multi-hazard assessment that can be used to face and manage coastal hazards.

Rockfall runout, Mount Cimone area, Emilia-Romagna Region, Italy

Numerous mass movements of different typology characterize both mountainous and piedmont sectors of the Emilia-Romagna Region (Apennine chain, North Italy). Although a less spatially frequent landslide typology within the region, rock falls represent severe threats to buildings, roads and persons due to their high propagation velocity. This paper presents an extract of the Emilia-Romagna regional map of the rock fall runout areas at a scale of 1:25,000. The analysis of rock fall runout areas was based upon a three-dimensional morphological method (TDM). The zone presented in the Main Map encompasses the area surrounding Mount Cimone, in the Emilia-Romagna Region. The proposed regional map of rockfall runout is noteworthy for planning actions and strategies aimed at the prevention and reduction of landslide risk at a regional scale.

Stream Length-Gradient Index Mapping as a Tool for Landslides Identification

The Stream Length-Gradient (SL) index is used to detect knickpoints potentially related to surface and sub-surface deformation processes. In this work, the SL index has been calculated along streams draining the southern sector of the Emilia-Romagna Region within the Northern Apennines (Italy), to detect knickpoints associated with active landslides. The methodology allowed the rapid analysis of an area of ca. 2300 km\(^{2}\). Approximately thirty hillslopes potentially affected by landslides were identified studying the SL index outlier values. Field survey confirmed the presence of large deep-seated landslides associated with 90 % of the observed anomalies. This study illustrates that stream profiles metrics may have a high potential in different geological studies covering wide areas in a short time and investing limited resources.

Integrated Monitoring of Lateral Spreading Phenomena Along the North-West Coast of the Island of Malta

Landslides, and especially lateral spreading, are responsible for the main landforms observable along the north-western coast of the Island of Malta. A series of rock spreading phenomena, and associated mass movements, have been recognised in this area and the most significant cases have been investigated by means of a multi-technical approach which envisaged geomorphological survey and mapping, geophysical analyses and monitoring of displacements. The aim of the study was to define whether rock spreading phenomena are active along the investigated coastal stretch and, possibly, to determine the rate of movement of the most relevant cases. In this framework, a multidisciplinary approach was used and different techniques were tested and applied on a specific site, which was selected for the presence of an extensive rock spread phenomenon which may induce hazard conditions. The site is located at Il-Prajjet (Anchor Bay), a narrow inlet where a tourist attraction is located. Research activities have been carried out at Il-Prajjet since 2006 when a GPS network of eight benchmarks was installed. This technique was chosen because it proved to be a powerful tool in the study of similar ground deformation in coastal and mountain areas, showing high accuracy and reliability. Once GPS monitoring had showed that rock spreading was active, further techniques were applied in order to achieve an in-depth knowledge of the instability processes occurring at Il-Prajjet. The paper illustrates the results so far achieved thanks to GPS monitoring, tape extensometer measurements, SAR interferometric analyses and GPR investigations.