Deep-seated Gravitational Slope Deformation Research Articles

Large landslide stress states calculated during extreme climatic and tectonic events on El Hierro, Canary Islands

Composed volcanic edifices are particularly prone to large-scale failures—these often result from the acceleration of preexisting deep-seated gravitational slope deformations. Consequently, a complete understanding of the kinematic behaviour of such slope deformations would represent an important step towards mitigating against human casualties or fatalities and damage to critical infrastructure. In this manuscript, a 9-month time series of three-dimensional fault displacement measurements has been used to determine the stress states of the San Andres Landslide on El Hierro in the Canary Islands. These stress states have been calculated on the basis of single-displacement events using a novel approach which only requires information about the magnitude of the movement vector and its orientation. The analysis focused on four specific periods: a reference period in November 2013; an extreme rainfall event at the beginning of December 2013; and two endogenous impulses at the end of December 2013 and during the middle of March 2014. On the basis that the direction of principal stress represents a marker for the direction of landslide mass movement, it has been possible to define six landslide activity modes which correspond to specific stress states. The response of the landslide to the extreme rainfall event was immediate and reflected increasing saturation of the porous landslide mass. The response of the landslide to the endogenous impulses was more complicated as compressional pulses often alternated with gravitational relaxation. In this study, it is demonstrated that the landslide stress state can be determined on the basis of a single-displacement event whenever fault displacements are monitored in three dimensions. This innovative approach may represent a valuable step towards a complete understanding of the kinematic behaviour of potentially catastrophic slope deformations, particularly those which are in a critical stability state.

Large bedrock slope failures in a British Columbia, Canada fjord: first documented submarine sackungen

Very large (>60×106 m3) sackungen or deep-seated gravitational slope deformations occur below sea level along a steep fjord wall in central Douglas Channel, British Columbia. The massive bedrock blocks were mobile between 13 and 11.5 thousand radiocarbon years BP (15,800 and 13,400 BP) immediately following deglaciation. Deformation of fjord sediments is apparent in sedimentary units overlying and adjacent to the blocks. Faults bound the edges of each block, cutting the glacial section but not the Holocene sediments. Retrogressive slides, small inset landslides as well as incipient and older slides are found on and around the large failure blocks. Lineations, fractures and faults parallel the coastline of Douglas Channel along the shoreline of the study area. Topographic data onshore indicate that faults and joints demarcate discrete rhomboid-shaped blocks which controlled the form, size and location of the sackungen. The described submarine sackungen share characteristic geomorphic features with many montane occurrences, such as uphill-facing scarps, foliated bedrock composition, largely vertical dislocation and a deglacial timing of development.

Activity and kinematic behaviour of deep-seated landslides from PS-InSAR displacement rate measurements

Large landslides and deep-seated gravitational slope deformations (DSGSD) represent an important geo-hazard in relation to the deformation of large structures and infrastructures and to the associated secondary landslides. DSGSD movements, although slow (from a few millimetres to several centimetres per year), can continue for very long periods, producing large cumulative displacements and undergoing partial or complete reactivation. Therefore, it is important to map the activity of such phenomena at a regional scale. Ground surface displacements at DSGSD typically range close to the detection limit of monitoring equipment but are suitable for synthetic aperture radar (SAR) interferometry. In this paper, permanent scatterers (PSInSAR™) and SqueeSAR™ techniques are used to analyse the activity of 133 DSGSD, in the Central Italian Alps. Statistical indicators for assigning a degree of activity to slope movements from displacement rates are discussed together with methods for analysing the movement and activity distribution within each landslide. In order to assess if a landslide is active or not, with a certain degree of reliability, three indicators are considered as optimal: the mean displacement rate, the activity index (ratio of active PS, displacement rate larger than standard deviation, overall PS) and the nearest neighbor ratio, which allows to describe the degree of clustering of the PS data. According to these criteria, 66% of the phenomena are classified as active in the monitored period 1992–2009. Finally, a new methodology for the use of SAR interferometry data to attain a classification of landslide kinematic behaviour is presented. This methodology is based on the interpretation of longitudinal ground surface displacement rate profiles in the light of numerical simulations of simplified failure geometries. The most common kinematic behaviour is rotational, amounting to 41 DSGSDs, corresponding to the 62.1% of the active phenomena.

Kinematic Reconstruction of a Deep-Seated Gravitational Slope Deformation by Geomorphic Analyses

On 4 November 2010, a deep-seated gravitational slope deformation (North Italy) reactivated with sudden ground movement. A 450,000 m2 mountainous area moved some metres downslope, but the undeniable signs were only connected to the triggering of a debris flow from the bulging area’s detrital cover and the presence of a continuous perimeter fracture near the crown area. Based on two detailed LiDAR surveys (2 m × 2 m) performed just a few days before and after the event, a quantitative topographic analysis was performed in a GIS environment, integrating morphometric terrain parameters (slope, aspect, surface roughness, hill shade, and curvature). The DEMs analysis highlighted some morphological changes related to deeper as well as shallow movements. Both global and sectorial displacements were widely verified and discussed, finally inferring that the geometry, persistence, and layout of all movements properly justify each current morphostructure, which has the shape of a typical Sackung-type structure with impulsive kinematics. Moreover, a targeted field survey allowed specific clues to be found that confirmed the global deduced dynamics of the slope deformation. Finally, thanks to a ground-based interferometric radar system (GB-InSAR) that was installed a few days after the reactivation, the residual deep-seated gravitational slope deformation (DSGSD) movements were also monitored. In the landslide lower bulging area, a localized material progression of small entities was observed for some months after the parossistic event, indicating a slow dissipation of forces in sectors more distant from the crown area.

Tectonically Induced Deep-Seated Gravitational Slope Deformations and Large Landslides in the Central Adriatic Coastal Belt (Southern Marche-Abruzzi, Italy)

Tectonically Induced Deep-Seated Gravitational Slope Deformations and Large Landslides in the Central Adriatic Coastal Belt (Southern Marche-Abruzzi, Italy)

Coastal cliffs, rock-slope failures and Late Quaternary transgressions of the Black Sea along southern Crimea

Rock-slope failures represent a significant hazard along global coastlines, but their chronology remains poorly documented. Here, we focus on the geomorphology and chronology of giant rockslides affecting the Crimean Mountains along the Black Sea coast. Geomorphic evidence suggests that high (>100 m) limestone cliffs flanking the southern slopes of the Crimean Mountains are scarps of rockslides nested within larger deep-seated gravitational slope deformations (DSGSDs). Such pervasive slope failures originated due to lateral spreading of intensively faulted Late Jurassic carbonate blocks moving atop weak/plastic Late Triassic flysch and tuff layers. By introducing a dating strategy relying on the combination of the uranium-thorium dating (U-Th) of exposed calcareous speleothems covering the landslide scarps with the 36Cl exposure dating of rock walls, we are able to approximate the time interval between the origin of incipient crevices and the final collapse of limestone blocks that exposed the cliff faces. For the three representative large-scale rockslides between the towns of Foros and Yalta, the initiation of the DSGSDs as evidenced by the widening of crevices and the onset of speleothem accumulation was >300 ka BP, but the recent cliff morphology along the coast is the result of Late Pleistocene/Holocene failures spanning ∼20–0.5 ka BP. The exposures of rockslide scarps occurred mostly at ∼20–15, ∼8, ∼5–4 and ∼2–0.5 ka, which substantially coincide with the last major Black Sea transgressions and/or more humid Holocene intervals. Our study suggests that before ultimate fast and/or catastrophic slope failures, the relaxation of rock massifs correlative with karstification, cracks opening, and incipient sliding lasted on the order of 104–105 years. Rapid Late Glacial/Holocene transgressions of the Black Sea likely represented the last impulse for the collapse of limestone blocks and the origin of giant rockslides, simultaneously affecting the majority of the SW coast of the Crimean Peninsula.

GB-InSAR monitoring of slope deformations in a mountainous area affected by debris flow events

Abstract. Diffuse and severe slope instabilities affected the whole Veneto region (north-eastern Italy) between 31 October and 2 November 2010, following a period of heavy and persistent rainfall. In this context, on 4 November 2010 a large detrital mass detached from the cover of the Mt. Rotolon deep-seated gravitational slope deformation (DSGSD), located in the upper Agno River valley, channelizing within the Rotolon Creek riverbed and evolving into a highly mobile debris flow. The latter phenomena damaged many hydraulic works, also threatening bridges, local roads, and the residents of the Maltaure, Turcati, and Parlati villages located along the creek banks and the town of Recoaro Terme. From the beginning of the emergency phase, the civil protection system was activated, involving the National Civil Protection Department, Veneto Region, and local administrations' personnel and technicians, as well as scientific institutions. On 8 December 2010 a local-scale monitoring system, based on a ground-based interferometric synthetic aperture radar (GB-InSAR), was implemented in order to evaluate the slope deformation pattern evolution in correspondence of the debris flow detachment sector, with the final aim of assessing the landslide residual risk and managing the emergency phase. This paper describes the results of a 2-year GB-InSAR monitoring campaign (December 2010–December 2012) and its application for monitoring, mapping, and emergency management activities in order to provide a rapid and easy communication of the results to the involved technicians and civil protection personnel, for a better understanding of the landslide phenomena and the decision-making process in a critical landslide scenario.

SH-wave seismic reflection at a landslide (Patigno, NW Italy) integrated with P-wave

The aim of this paper is to present the acquisition and processing up to the depth migrated section of an SH-wave reflection seismic profile. This experience is conducted on a deep-seated gravitational slope deformation located in the Northern Apennines in Italy. The SH-wave depth-migrated image in the investigated area provides a detailed description of the small reactivation slip surfaces delineating minor landslides at shallow depths, which are responsible for the major damages observed. These results are integrated with a recently acquired P-wave seismic reflection profile investigating the same slope and delineating the highly deformed layer at depth, liable for the deep-seated gravitational slope deformation. The combined use of P-waves and SH-waves allows to gain a deeper knowledge of the landslide internal setting that is necessary to mitigate the risk associated with the mass movement.

Evolving slope instability zone at Mt. Turzyna (Sudetes, SW Poland) – An example of incipient deep-seated gravitational slope deformation

Evolving slope instability zone at Mt. Turzyna (Sudetes, SW Poland) – An example of incipient deep-seated gravitational slope deformation

Gravitational slope-deformation of a resurgent caldera: New insights from the mechanical behaviour of Mt. Nuovo tuffs (Ischia Island, Italy)

Ischia Island (Italy) is an impressive example of the rare phenomenon of caldera resurgence. The emplacement and replenishment of magmas at shallow depth resulted in a vertical uplift of about 900m, concentrated in the western portion of Mt. Epomeo (789m a.s.l.). As a consequence of this uplift, the island has experienced several slope instabilities at different scales since the Holocene, from shallow mass movements to large rock and debris avalanches. These mass wasting events, which mobilised large volumes of greenish alkali-trachytic tuff (the Mt. Epomeo Green Tuff, MEGT), were strictly related to volcano-tectonic activity and the interaction between the volcanic slopes and the hydrothermal system beneath the island. Deep-Seated Gravitational Slope Deformation (DSGSD) at Mt. Nuovo, located adjacent to densely populated coastal villages, is an ongoing process that covers an area of 1.6km2. The Mt. Nuovo DSGSD involves a rock mass volume of 190Mm3 and is accommodated by a main shear zone and a series of sub-vertical fault zones associated with high-angle joint sets. To improve our understanding of this gravity-induced process, we performed a physical (porosity and permeability) and mechanical (uniaxial and triaxial deformation experiments) characterisation of two ignimbrite deposits - both from the MEGT - that form a significant component of the NW sector of Mt. Epomeo. The main conclusions drawn from our experiments are twofold. First, the presence of water dramatically reduces the strength of the tuffs, suggesting that the movement of fluids within the hydrothermal system could greatly impact slope stability. Second, the transition from brittle (dilatant) to ductile (compactant) behaviour in the tuffs of the MEGT occurs at a very low effective pressure, analogous to a depth of a couple of hundred metres, and that this transition is likely moved closer to the surface in the presence of water. We hypothesise that compactant (porosity decreasing) behaviour at the base of the layer could therefore facilitate slope instability. Although our results show that transient exposure to 300°C does not influence the short-term strength of the tuff, we speculate that the high in-situ temperature could increase the efficiency of brittle and compactant creep and therefore increase the rate of slope deformation. Taken together, our experimental data highlight a potentially important role for the hydrothermal system (that reaches a minimum depth of ~1km) in dictating the DSGSD at Mt. Nuovo. An understanding of this deformation process is not only important for the proximal coastal villages, at risk of engulfment by a large debris avalanche, but also for the towns and cities along the coast of the Gulf of Naples that are at risk to a secondary consequence of such an avalanche - a tsunami wave.

Impact of massive deep-seated rock slope failures on mountain valley morphology in the northern Cottian Alps (NW Italy)

ABSTRACTDeep-seated rock slope failures represent effective mechanisms of natural rock mass-wasting, able to radically change mountain-valley morphology. In the northern Cottian Alps, an extraordinary concentration of instability phenomena occurs in extensive areas of the Susa and Chisone valleys. In the Main Map, at a scale of 1:30,000, a new representation of these deep-seated rock slope failures is proposed. Major effort has been invested in properly distinguishing between sackung-type deep-seated gravitational slope deformations and large landslides. Gravitational phenomena have affected the mountain landscape, with the development of impressive morphostructural features such as multiple-crested ridges and ridge top depressions. In the middle and distal portions of the slopes, sagging and toe bulging impose a marked change in the valley-slope profiles, in turn inducing secondary slope instabilities. Furthermore, mature deep-seated gravitational deformations and large landslides have, in some cases, made a significant impact on valley bottom morphology due to a partial or complete valley dam.

Geology and mass movements of the Licetto River catchment (Calabrian Coastal Range, Southern Italy)

ABSTRACTThe paper presents a detailed mass movement inventory map of the Licetto River basin, an intermountain catchment of 50 km2 formed during the Quaternary in response to extensional tectonics dissecting fold-and-thrust belts of the Calabrian Coastal Range (Southern Italy). The map (Main Map) is the result of both an integration between geological and morphological data derived from the visual analysis of aerial photographs at different times and scales, and the collection of new data obtained from multi-temporal field surveys. The study area is affected by a total of 824 mass movements, frequently made by superimposed bodies of different types, states of activity and sizes, including some kilometre-scale Deep-Seated Gravitational Slope. The majority of the mapped landslides, mainly of slide type, involve low-grade metamorphic rocks which also show the exclusive presence of deep-seated gravitational slope deformations. Analysis of the inventory map revealed that 40% of the mapped landslides, often attributable to very slow-moving landslides, can be considered active. The Main Map represents a useful tool for territorial planning and engineering – geological and environmental purposes in this complex geo-structural area, providing a useful contribution for quantitative landslide risk analyses and the design of appropriate risk-mitigation measures.

Coupling fluvial processes and landslide distribution toward geomorphological hazard assessment: a case study in a transient landscape in Japan

This study quantified the relationship among deep-seated gravitational slope deformations (DGSDs), landslides, and river rejuvenation in the upper reaches of the Kumano River in the Kii Mountains of Japan, an area of frequent bedrock landslides. River profiles and hillslope landforms were examined, and high-resolution digital elevation models (DEMs) were used to identify DGSDs and landslides. Many of the deep-seated landslides were associated with rainstorms in 1889 and 2011. Landslide volumes were related to landslide areas on the basis of 52 deep-seated landslides that failed during the 2011 rainfall, providing basic data for landscape denudation and sediment yield. River rejuvenation occurred stepwise, incising moderate relief paleosurfaces and forming two series of knickpoints and V-shaped inner gorges that are up to 400-m deep. More than 65% of DGSDs and 75% of the landslides were located in association with the incised inner gorges along the peripheries of the paleosurfaces or were entirely contained within the inner gorges. DGSDs and landslides associated with the incised inner valley slopes tended to be larger than those developed within the paleosurfaces and may be long-term transient hillslope responses to river incision. Hillslope undercutting caused by rejuvenated river incision may play an important role in long-term slope stability and distribution of mass movements, and could serve as an indicator of landslide hazard.

From incipient slope instability through slope deformation to catastrophic failure — Different stages of failure development on the Ivasnasen and Vollan rock slopes (western Norway)

The long-term evolution of rock slope failures involves different stages, from incipience of slope instability to catastrophic failure, through a more or less long-lasting slope deformation phase that also involves creeping or sliding. Topography, lithology, and structural inheritance are the main intrinsic factors that influence this evolution. Here, we investigate the role of these intrinsic factors on the rock slope failure development of the Ivasnasen and Vollan rock slopes (Sunndal Valley, western Norway) using a multitechnique approach that includes geomorphologic and structural field mapping, kinematic analysis, terrestrial cosmogenic nuclide exposure dating, topographic reconstruction, and deformation quantification. Ivasnasen is a rock slope failure complex with several past rock slope failures and a present unstable rock slope, located on a cataclinal NW-facing slope and developed in augen gneiss. Vollan on the opposite valley side is a deep-seated gravitational slope deformation (DSGSD) affecting the whole mountainside, developed in quartzite in the upper part and micaschist in the lower part. These different lithologies belong to different nappe complexes that were emplaced and folded into a series of syn- and anticlines during the Caledonian orogeny. These folds lead to different lithologies being exposed in different structural orientations on the opposite valley flanks, which in turn leads to different types and evolution of rock slope failures. At Ivasnasen the 45°–55° NW-dipping ductile foliation allowed for a fairly simple planar sliding mechanism for the 1.2millionm3 post-glacial rock slope failure. Failure occurred ca. 3.3ka ago after a short period of prefailure deformation. For the present 2.2millionm3 unstable rock slope at Ivasnasen, a steepening of the foliation at the toe impedes such a mechanism and up to 10m of displacement has not lead to a catastrophic failure yet. The Vollan DSGSD is characterized by a steep major back scarp with its up to 130-m-wide graben, which opened along the subvertical foliation in the quartzite, and a conspicuous array of counter-scarps in the micaschist. The morphologic features are explained by a flexural toppling mechanism in the micaschist, which likely initiated in the lower slope section and propagated retrogressively until reaching the massive quartzite at the back scarp. Flexural toppling cannot solely explain the total along-slope displacement of up to 200m, i.e., an elongation of 28%. Creep along a basal shear zone, which may have developed in the hinge zone of the flexural toppling, combined with shallow valley-dipping joints, likely accounts for the large elongation. Implications of this study for the hazard assessment of unstable rock slopes in Norway include the relatively rapid development of instabilities in cataclinal slopes and the important insights on long-term displacement rates gained from cosmogenic nuclide dating for a better understanding of the evolution of unstable rock slopes.

The Acheron Dorsum on Mars: A novel interpretation of its linear depressions and a model for its evolution

The Acheron Dorsum north of Olympus Mons on Mars is a unique 800 km-long arcuate ridge apparently unrelated to other adjacent morphologies. Acheron Dorsum is crossed by deep and wide fractures (“fossae”, here referred to also as Linear Depressions or “LDs”), commonly interpreted as grabens formed by local lithosphere stress in response to endogenous mantle upwelling. We suggest an alternate view that the linear depressions may result from gravitational self-adjustment of a loose deposit similar to the Deep-Seated Gravitational Slope Deformations (DSGSD or Sackung), a kind of slow mass movement well documented on Earth. Numerical simulations based on a finite difference numerical model devised for terrestrial DSGSDs reproduce the timing and position of LDs reasonably well provided that the viscosity of the viscoplastic layer is between ≈71015 and ≈1017 Pas. While rock masses typically exhibit much higher values, based on comparison with glacial examples, we find that these viscosities could be compatible to a rock–ice mixture.This leads to the hypothesis that the rock underneath Acheron Dorsum may be highly fragmented and that ice might have been involved in its deformation. Our hypothesis could shed light on the puzzling stress pattern on Acheron Dorsum, which follows approximately the ridge, without requiring the presence of hypothetical small-scale, endogenous currents.

Clustering sediment connectivity maps to distinguish hillslope processes

The availability of increasingly higher resolution Digital Terrain Models (DTMs) allows to perform a detailed characterization of the morphological features on selected areas of interest. There is a growing interest, within the scientific community, for automatic DTM-based procedures to extract geomorphological features or to model surface processes. Among these, the Index of sediment Connectivity (IC), which estimates the degree of linkage that controls sediment fluxes throughout landscape, and, in particular, between sediment sources and downstream areas, has proved to be a powerful morphometric tool. In particular, IC may be used to better portray and highlight sediment dynamics and pathways at catchment scale. In this work, we compare IC maps for two alpine areas. The first area is a typical debris-flow catchment, while the second areais characterized by the presence of a large deep-seated gravitational slope deformation. Two types of numerical analysis are presented:i) the aggregation and normalization of the IC values and ii) cluster analysis. Our preliminary results show that the spatial information, which is maintained in the cluster analysis and lost in the aggregate procedure, is extremely valuable for the identification and the clustering of areas that are affected by the same predominant geomorphological process.

The nature of annual lamination in carbonate flowstones from non-karstic fractures, Vinschgau (northern Italy)

The Vinschgau is an inneralpine valley in the Southern Alps, whose steep flanks are composed of strongly sheared gneisses and schists affected by deep-seated gravitational slope deformations. Fractures generated by these movements host a groundwater system characterised by high amounts of dissolved solids, which reflect long residence times and water-rock interactions driven by sulphide oxidation. This, in combination with high air and soil temperatures on the south-facing slope (Sonnenberg) of the valley favoured the deposition of calcite and aragonite flowstone in shallow parts of this fractured, non-karstic aquifer. About 5% of these speleothems exhibit well-developed regular lamination, whose annual origin was confirmed by radiometric dating. A stable isotope, petrographic and trace element study combined with U-Th dating was undertaken to disentangle the processes controlling lamina formation. A succession of darker and lighter laminae forms distinct macroscopic couplets (0.2–2mm wide) in three of the samples, while one sample comprises alternating white and translucent laminae. Microscopically, the darker and white laminae show a higher abundance of opaque particles, whose organic origin is confirmed by their strong epifluorescence. The crystal fabric is dominated by the fascicular-optic type. The calcite shows regular δ18O oscillations with an amplitude of up to 1.2‰. With the exception of one sample, δ13C lacks such a regular pattern, and only shows smaller variations which do not correlate with δ18O in a consistent way. All samples exhibit regular, low-amplitude Mg, Sr, Ba and U cycles. In three samples Mg shows oscillations similar to the δ18O cycles in their frequency, but opposite in phasing. δ18O and Mg oscillations are primarily attributed to surface temperature variations that are transmitted to the shallow subsurface by thermal conduction. Low-amplitude trace element cycles (Mg, Sr, Ba and U) are most probably driven by intra-annual variations in the degree of prior aragonite precipitation in the seepage path which relates to seasonal changes in evaporation.

The Benner pass rock avalanche cluster suggests a close relation between long-term slope deformation (DSGSDs and translational rock slides) and catastrophic failure

In mountain ranges deep-seated gravitational slope deformations (DSGSDs) and extremely rapid mass wastings of rock >105m3 in volume (catastrophic rock-slope failures, CRF) are present, yet their mutual relation is poorly documented. Near the Brenner Pass (1370m asl) in the eastern Alps, five catastrophic rock-slope failures of medium- to high-grade metamorphites are clustered (‘Brenner Pass Cluster’; BPC), and three of them are related to DSGSDs. The catastrophic rock-slope failures involved volumes from 12 to 110Mm3 and show fahrboeschung angles of 10–27°. Numerical dating (14C, 234U/230Th) suggests that all catastrophic slope failures of the BPC occurred between ≤13.5 and 6.2ka. Three of the CRF events may have occurred during the Younger Dryas (12.7–11.7ka), whereas two events occurred during the Holocene. Backwater basins dammed up by the CRFs range from 2.5km2 (Ridnaun rock avalanche) to 15.5km2 (Stilfes rock avalanche).Three of the catastrophic rock-slope failures are associated with and developed as a partial failure of a DSGSD. This suggests that progressively slow deformation of slopes ultimately exceeded a stability threshold, resulting in catastrophic rock-slope failures. The initial kinematic mechanisms of failure vary between large-scale toppling, wedge sliding, and planar sliding and are strongly controlled by the structural setting of the slopes.A direct connection of catastrophic mass wasting with specific palaeoclimatic conditions (e.g., phases of enhanced precipitation) is not indicated; however, this does not exclude specific meteorological situations (e.g., occurrence of short-term heavy rainfall) that may have expedited slope instability and perhaps even triggered catastrophic events.Attempts to correlate catastrophic rock-slope failures with specific palaeoclimatic regimes are still encumbered by substantial methodical uncertainties and imprecisions as well as the scarcity of dated CRF events. The mapped distribution of CRFs unequivocally indicates that structural predisposition is the most significant long-term control in forming CRF clusters.

The August 24th 2016 Accumoli earthquake: surface faulting and Deep-Seated Gravitational Slope Deformation (DSGSD) in the Monte Vettore area

<p>On August 24th 2016 a Mw=6.0 earthquake hit central Italy, with the epicenter located at the boundaries between Lazio, Marche, Abruzzi and Umbria regions, near the village of Accumoli (Rieti, Lazio). Immediately after the mainshock, this geological survey has been focused on the earthquake environmental effects related to the tectonic reactivation of the previously mapped active fault (i.e. primary), as well as secondary effects mostly related to the seismic shaking (e.g. landslides and fracturing in soil and rock).This paper brings data on superficial effects and some preliminary considerations about the interaction and possible relationship between surface faulting and the occurrence of Deep-Seated Gravitational Slope Deformation (DSGSD) along the southern and western slope of Monte Vettore.</p>

An example of active DSGSD in the Carnian Alps (NE Italy)

In the northern part of Friuli Venezia Giulia Region (Italy), in the Carnic Alps, above the Cercevesa stream, an active mass movement has been recently identified and classified as Deep Seated Gravitational Slope Deformation (DSGSD). The phenomenon covers an area of about 0.5 km2 and involves limestones overlying sandstones and mudstones. The most evident morphological feature of the Cercevesa DSGSD is a double-crested ridge on the top of the slope. The first measurements, recorded since June 2008, show a constant opening rate of about 58 cm/yr, a really rare value for gravitational phenomena in the Alps. To detect the triggering factor, geomorphological data, meteorological time series (rainfall, snowfall and temperature) and seismological data have been analyzed. The comparative analysis highlighted that the persistent rainfall of mid-November 1990 can be identified as the root cause of the phenomenon.