Sibillini Mts Research Articles

DIGITAL INVESTIGATION OF LAMNIFORM SHARK VERTEBRAE FROM THE SIBILLINI MTS. (NORTHERN APENNINES, ITALY)

During the sampling of a stratigraphic section along the shore of the Fiastra Lake (Carg Project - Sheet 313 “Camerino” of the Geological Map of Italy at 1:50 000 scale), a small rock boulder with partially exposed bony material was discovered at the base of a small cliff at the northern termination of the Sibillini Mts. In this area, the classical facies of Umbria-Marche stratigraphic succession are well exposed. The Oligocene-Miocene portion of the succession is represented by the ~200 m-thick Scaglia Cinerea Formation, passing upwards to the ~100 m-thick Bisciaro Formation. The microfossil assemblage has allowed the specimen to be constrained to the lower Burdigalian. The skeletal remains were examined using a CT-SCAN, a non-invasive method that has proven to be highly performing. The analysis revealed some articulated vertebrae, deformed by lithostatic compaction, which are attributed to a shark of the Order Lamniformes. Subsequently, the vertebrae were digitally isolated, extracted from the surrounding matrix, and rendered into three-dimensional prints. Through digital retro-deformation, the body length of the lamniform shark was estimated to be approximately 4 metres. Further considerations on the vertebrae allowed us to infer that the studied shark had similarities to either Isurus oxyrinchus Rafinesque, 1810 or Carcharodon carcharias Linnaeus, 1758. The development of a dead-fall microbial community likely facilitated the preservation of the vertebrae. The studied specimen represents the first occurrence of a lamniform shark in the Lower Miocene of the Umbria-Marche Domain and represents one of the very rare recorded occurrences of lamniforms from the Lower Miocene of Italy.

Co-Occurrence of Earthquake and Climatic Events on Groundwater Budget Alteration in a Fractured Carbonate Aquifer (Sibillini Mts.—Central Italy)

The combination of several factors related both to human pressure as well as natural issues could lead to a marked alteration of the groundwater budget terms and a decrease in groundwater availability. The basal aquifer of the Sibillini Mts. is a strategic resource of drinking water in the central sector of Apennine (Italy). The seismic sequence that occurred in this area in 2016 induced transient and sustained modifications in the aquifer settings. Springs located on the western side of the Sibillini Mts. were characterized by an increased discharge, while in contrast, the eastern springs suffered an intense drop in their groundwater discharge. In 2017, a drought period started immediately after the exhaustion of the seismic sequence effect. The comparison between the recharge and discharge of the major springs in the 2000–2020 period allowed the definition of the different responses of the aquifer to the co-occurrence of earthquakes and climatic events. The hydrodynamic alteration triggered by the earthquake induced a huge depletion of the groundwater stored in the eastern sector of the basal aquifer (at least 50 × 106 m3). The scarce recharge occurring in the following drought period (more than 30% of the average annual value) was not enough to restore the groundwater resources, causing a serious drinking water supply crisis in the main tapped springs in the eastern sector of the aquifer.

Architecture and permeability structure of the Sibillini Mts. Thrust and influence upon recent, extension-related seismicity in the central Apennines (Italy) through fault-valve behavior

The central Apennines are a fold-thrust belt currently affected by post-orogenic extensional seismicity. To constrain the influence that the inherited thrust-related structures exert on the present seismic behavior of the belt, we provide the high-resolution structural and hydraulic characterization of one of the most external exposed thrust fault systems of the central Apennines, the Sibillini Mts. Thrust Front (STF). We integrate structural mapping, multiscale structural analysis, and in situ air permeability on the brittle structural facies of the thrust zone. We also performed K-Ar dating of selected fault rocks to better constrain structural inheritance. The STF is defined by a complex, ∼300-m-thick deformation zone involving Meso-Cenozoic marl and limestone that results from the accommodation of both seismic and aseismic slip during shortening. Permeability measurements indicate that the low permeability (10−2 ÷ 10−3 D) of the marly rich host rock diminishes within the thrust zone, where the principal slip surfaces and associated S-C structures represent efficient hydraulic barriers (permeability down to ∼3 × 10−10 D) to sub-vertical fluid flow. Field data and K-Ar dating indicate that the STF began its evolution ca. 7 Ma (early Messinian). We suggest that the studied thrust zone may represent a barrier for the upward migration of deep fluids at the hypocentral depth of present-day extensional earthquakes. We also speculate on the influence that similar deformation zones may have at depth on the overall regional seismotectonic pattern by causing transient fluid overpressures and, possibly, triggering cyclic extensional earthquakes on normal faults prone to slip while crosscutting the earlier thrust zones (as per a classic fault valve behavior). This mechanism may have controlled the origin of the 2016−2017 central Apennines devastating earthquakes.

A Holistic Approach to Study Groundwater-Surface Water Modifications Induced by Strong Earthquakes: The Case of Campiano Catchment (Central Italy)

Carbonate aquifers are characterised by strong heterogeneities and their modelling is often a challenging aspect in hydrological studies. Understanding carbonate aquifers can be more complicated in the case of strong seismic events which have been widely demonstrated to influence groundwater flow over wide areas or on a local scale. The 2016–2017 seismic sequence of Central Italy is a paradigmatic example of how earthquakes play an important role in groundwater and surface water modifications. The Campiano catchment, which experienced significant discharge modifications immediately after the mainshocks of the 2016–2017 seismic sequence (Mmax = 6.5) has been analysed in this study. The study area is within an Italian national park (Sibillini Mts.) and thus has importance from a naturalistic and socio-economic standpoint. The research strategy coupled long-period artificial tracer tests (conducted both before and after the main earthquakes), geochemical and discharge analyses and isotope hydrology with hydrogeological cross-sections. This study highlights how the seismic sequence temporarily changed the behaviour of the normal faults which act predominantly as barriers to flow in the inter-seismic period, with water flow being normally favoured along the fault strikes. On the contrary, during earthquakes, groundwater flow can be significantly diverted perpendicularly to fault-strikes due to co-seismic fracturing and a consequent permeability increase. The interaction between groundwater and surface water is not only important from the point of view of scientific research but also has significant implications at an economic and social level.

New hydrogeological results on the Groundwater Dependent Ecosystem of the Pilato Lake (Sibillini Mts, Central Italy)

Located at an altitude of about 1950 m a.s.l. in a glacial cirque of Mount Vettore (Monti Sibillini National Park - Central Italy), Pilato Lake is one of the few glacial lakes existing in the Apennines. Due to the endemic presence of the crustaceous Chirocephalus marchesonii, the Pilato Lake was in the past mainly studied from the biological viewpoint, but hydrogeological information on this groundwater dependent ecosystem is scarce. Furthermore, for investigating the lake drying in the recent 2017, 2019 and 2020 summers, the seasonal lowering of lake levels during 2010, 2012 and 2014-2020 was reconstructed. It resulted that in the preseismic years, the lake emptying was slower than in the post-seismic time. It is then supposed that seismic quaking induced an increase in permeability and, consequently, increased infiltration velocity through the lake sustaining surficial (detrital and glacial) and/or bedrock deposits towards the subsurface. More frequent summer dryings of the lake are then supposed for the next future. The hydrogeological conceptual model of the study area showed that the refilling process of the lake is driven by snow and rain precipitations. The air temperatures during 2017-2020 and their effects on evaporation from lake and on actual evapotranspiration were estimated. The infiltration through sustaining sediments was calculated and the estimation with time of lake wet surface and lake volume variations, and then bulk permeability of sustaining sediments, were evaluated as well.

Fractured carbonate aquifers of Sibillini Mts. (Central Italy)

ABSTRACT The aim of the present map is to illustrate a detailed pre-earthquake hydrogeological conceptual model of the Sibillini Mts. This area was struck by a prolonged seismic sequence of up to Mw 6.5 in 2016. Geological, tectonic, and hydrogeological data were collected from the literature before 2016, subsequently standardized and re-interpretated with the aim of presenting a hydrogeological map (1:50,000 scale) of the Sibillini Mts. carbonate system (Central Italy). The map is supported by 11 hydrogeological both cross and longitudinal sections, which show the underground spatial relationship between aquifers, aquicludes, and tectonic elements. This Map provides a model of comparison for the new hydrogeological conditions emerging from the post-seismic research.

Geological map of the Mt. Vettoretto–Capodacqua area (Central Apennines, Italy) and cross-cutting relationships between Sibillini Mts. Thrust and Mt. Vettore normal faults system

We present the results of a geological mapping project performed in the southern portion of the Sibillini Mts., aimed at defining the structural relationships between the Sibillini Mts. Thrust front and the Mt. Vettore normal fault system, reactivated during the 2016-2017 central Italy seismic sequence. The Sibillini Mts. Thrust is characterised by a hanging wall where the Meso-Cenozoic Umbria-Marche succession crops out, while the footwall is represented by the Messinian Laga foredeep unit. The Mt. Vettore extensional fault system is formed by two main normal faults, the Castelluccio Plain and Mt. Vettoretto faults. Being the cross-cutting relationships between the structural elements hidden by a thick debris cover, they have been reconstructed analyzing the geometries of the hanging wall anticline of the Sibillini Mts. Thrust and other field constrains. This allowed us to conclude that the Sibillini Mts. Thrust was displaced by the Castelluccio Plain normal fault with a max throw of ~ 250 m. Both the Castelluccio Plain normal fault and the Sibillini Mts. Thrust are subsequently cut by the Mt. Vettoretto fault, which is inferred to reuse in part the inverted Sibillini Mts. Thrust plane.

Geomorphological evidence of debris flows and landslides in the Pescara del Tronto area (Sibillini Mts, Marche Region, Central Italy)

ABSTRACT In this paper, a geomorphological map of Pescara del Tronto area (Sibillini Mts, Marche Region) is presented. The work focuses on the geomorphological analysis performed in a zone strongly struck by the 2016–2017 seismic sequence of Central Apennines. The geomorphological map (1:7,500 scale) was obtained through an integrated approach that incorporates geological-geomorphological field mapping and geomorphological profile drawing, supported by air-photo interpretation and GIS analysis. The main purpose of the work is to describe a geomorphological approach for representing and mapping the evidence of several debris flows and landslides recognized in the framework of seismic microzonation (SM) activities. Finally, in order to elevate geomorphological maps into effective tools for land management and risk reduction, it could provide a scientific and methodological basis to demonstrate that accurate mapping provides important information, readily available for local administrations and decision-makers, for the implementation of sustainable territorial planning and loss-reduction measures.

Sustained post‐seismic effects on groundwater flow in fractured carbonate aquifers in Central Italy

AbstractA sustained increase in spring discharges was monitored after the 2016 Central Italy seismic sequence in the fractured carbonate aquifer of Valnerina–Sibillini Mts. The groundwater surplus recorded between August 2016 and November 2017 was determined to be between 400 and 500 × 106 m3. In fractured aquifers, the post‐seismic rise in spring discharges is generally attributed to an increase in bulk permeability caused by the fracture cleaning effect, which is induced by pore pressure propagation. In the studied aquifers, the large amount of additional discharge cannot only be attributed to the enhanced permeability, which was evaluated to be less than 20% after each main seismic event. A detailed analysis of the spring discharge hydrographs and of the water level at five gauging stations was carried out to determine the possible causes of this sudden increase in groundwater outflow. Taking into account the geological and structural framework, a conceptual model of a basin‐in‐series has been adopted to describe the complex hydrogeological setting, where the thrusts and extensional faults have clearly influenced the groundwater flow directions before and after the seismic sequence. The prevalent portion of the total post‐seismic discharge surplus not explained by the increase in permeability has been attributed to changes in the hydraulic gradient that caused seismogenic fault rupture and the disruption in the upgradient sector of the aquifer. The additional flow calculated through the breach of the pre‐existing hydrostructural barrier corresponds to approximately 470 × 106 m3. This value is consistent with the total discharge increase measured in the whole study area, validating the proposed conceptual model. Consequently, a shift in the piezometric divide of the hydrogeological system has been induced, causing a potentially permanent change that lowers the discharge amount of the eastern springs.

Mapping the geology of the 2016 Central Italy earthquake fault (Mt. Vettore – Mt. Bove fault, Sibillini Mts.): geological details on the Cupi – Ussita and Mt. Bove – Mt. Porche segments and overall pattern of coseismic surface faulting

We present the results of a field survey performed in the centralnorthern portion of the Mt. Vettore – Mt. Bove normal fault(VBF), reactivated during the 2016 central Italy earthquake sequence (24 August, Mw 6.0; 26 October Mw5.4 and Mw 5.9; 30 October Mw 6.5). The field survey was carried out by means of digital mapping techniques, and traditional methods on 1:10,000-scale topographic maps. The field work had two main aims: 1) to detail the geology of the central-northern VBF, and to constrain the segmentation and displacement distribution of the entire VBF system; and 2) to map in detail the ruptures of the 26 and 30 October events, filling in the gaps left by previous studies, and provide constraints on the coseismic parameters of the 2016 earthquakes.The results are summarized in a composite geological map, organized in 8 frames showing: the structural architecture in map view of the VBF system (frames 1 and 2); 1:25,000-scale geological maps of the Cupi-Ussita (frame 3) and Mt. Bove – Mt. Porche (frame 4) sectors of the VBF; twelve 1:25,000-scale geological sections for computing the geological displacements (frame 5); a summary of the coseismic parameters of the 2016 earthquakes (diagrams of net displacement, throw and opening; Surface Rupture Length, SRL; Maximum Displacement, MD and Average Displacement, AD) (frame 6); a comparison of the 2016 coseismic parameters with normal faulting earthquakes occurred globally (frame 7); and a computation of the morphological displacement (post-Last Glacial Maximum, LGM) across the VBF, a comparison among geological, morphological and coseismic displacements, and a quantification of the tectonic back-tilting in the area of maximum coseismic displacement (frame 8). Some implications are discussed in this accompanying note, such as the role of fault segmentation deduced from structural geology and tectonic geomorphology in controlling the coseismic displacement, the role of back-tilting in amplifying the coseismic displacement and the limits of empirical regressionsin predicting the relations between rupture parameters and Mw in case of segmented normal faults.

Quaternary negative tectonic inversion along the Sibillini Mts. thrust zone: the Arquata del Tronto case history (Central Italy)

Geological and geophysical investigations have been carried out in the surroundings of the villages of Pretare and Piedilama, in the Central Apennines. This area, located at the footwall of the prominent NNE–SSW oriented Sibillini thrust front, was struck by the August 24th 2016 Mw 6 earthquake. The results of the geological field survey combined with geological and geophysical subsurface investigations are here illustrated by a detailed geological map and by two significant cross-sections. The studied area is crossed by the Fosso di Morricone valley that, entrenched within the Messinian pelitic-arenaceous succession of the Laga formation, hosts a Late Pleistocene palaeo-landslide. The study evidences the occurrence of a N 10° oriented west dipping normal fault, here named Pretare–Piedilama fault, that controlled the left side of the Fosso di Morricone valley, producing a vertical displacement of the palaeo-landslide deposits of about 50 m. The geological, geomorphological and geophysical data indicate that the fault was active during the Late Pleistocene and part of the Holocene thus constraining a minimum vertical displacement-rate of 0.4 mm/a in the last 125 ka. The geometry of the deformed Laga formation cut by the fault suggests to relate it to the Late Quaternary negative tectonic inversion of a previous thrust plane located in the footwall of the Sibillini thrust front. The Pretare–Piedilama fault would represent the easternmost tectonic expression of this main potentially active structure. Future researches could be addressed to detail the age and the actual motion-rate of the structure and to define its seismic hazard assessment.

Fault Segmentation as Constraint to the Occurrence of the Main Shocks of the 2016 Central Italy Seismic Sequence

AbstractWe perform the finite‐extent fault inversion of the three main events of the 2016 Central Italy seismic sequence using near‐source strong motion records. We demonstrate that both earthquake nucleation and rupture propagation were controlled by segmentation of the (N)NW‐(S)SE trending Quaternary normal faults. The first shock of the sequence (24 August,Mw6.0) ruptured at the relay zone between the Laga Mts (LF) and the Cordone del Vettore (CVF) normal faults. The second shock (26 October,Mw5.9) nucleated at a minor relay zone within the Mt. Vettore‐Mt. Bove fault (VBF), while the third and largest one (30 October,Mw6.5) initiated at the relay zone between the VBF and CVF, triggering the multiple rupture of the VBF, CVF, and probably LF. We show that this latter relay zone corresponds to the deeper, high‐angle, fault zone of the Sibillini Mts cross structure, a thrust‐ramp inherited from the Miocene‐Pliocene contractional phase of the Apennines. This structure acted as a barrier to rupture propagation of the first two events thus defining an area of large stress concentration until it acted as the initiator of the rupture originating the largestMw6.5 event that crossed the barrier itself. We suggest that the “young” CVF have started to cut through the barrier acting as a soft‐linkage between the two long‐lived LF and VBF. The evidence that coseismic cumulative slip shows a maximum at the CVF, provided by both slip inversion and original surface rupture data, suggests that the CVF is growing faster than the adjacent faults.

Stratigraphic and structural features of the Sibillini Mountains (Umbria-Marche Apennines, Italy)

In this paper we illustrate the stratigraphic and structural features of the Sibillini Mountains on the basis of a 1:40.000 geological map. Following the “Foglio 132 Norcia” (Geological Map of Italy at 1:100.000 scale; [Scarsella, 1941][1]), this new geological map is the first cartographic document that covers the whole area of the Sibillini Mts. This area is key for understanding the geological evolution of the external zones of the Apennine orogen, mostly owing to the pronounced structural elevation of the Apennine ridge at the Sibillini Mts. area. This allowed us to: a ) carry out stratigraphic and structural analyses for the Umbria-Marche sedimentary cover to the oldest units; b ) analyze the paleotectonic setting of this sector of the Afro-Adriatic continental margin and the behavior of pre-existing structures during the subsequent deformation events; c ) investigate in depth the major Apennine thrust front (“Sibillini Mountains Thrust”) exposed in several sites (Fiastrone, Ambro, Tenna and Tronto valley) and its relationship with the units of the adjacent Messinian foredeep. Inherited (pre-thrusting) structures played an important role on the tectonic evolution of the study area. In addition to those of Jurassic age, associated to thinning of the Adriatic continental margin (the most frequent), there are also some Cretaceous-Eocene extensional faults and others probably related to Miocene foreland deformation. These extensional faults show very limited, or none, reversal of slip during contractional neogenic deformation. Usually they were tilted and, subsequently, displaced by thrust faults; locally they were deformed by buttressing processes. The paleotectonic setting also influenced the development of minor folds, as is evident in the Mt. Bove anticlinorium. Shortening-related structures are mainly represented by asymmetric, northeast-verging thrust-related anticlines involving Mesozoic-Tertiary sedimentary successions. Among these structures, the most important and well-known is the Sibillini Mts. Thrust, which bounds the Apennine mountain front, separating it from the Marche-Abruzzi foothills. This major fault affects the eastern, vertical to overturned, limb of the arcuate shaped Mt. Fiegni-Mt. Vettore anticline, which shows several complications, mostly due to the occurrence of minor thrust splays forming isolated lens-shaped tectonic slices up to several kilometers-long. The geological cross sections show that in the southernmost part of the Sibillini Mts. Thrust the displacement is partly buried and forms a detachment located at the base of the Laga Fm. Much of the Neogene compressional structures has been dissected by NNW-SSE trending Quaternary normal and oblique-slip faults, some of which reactivated older extensional structures. These faults do not seem to crosscut the Sibillini Mts. Thrust. Some of them show fresh fault scarps in the substrate and/or affect recent continental deposits and are considered responsible for the intense seismic activity of the area. [1]: #ref-141

A proposal for compiling quantitative hydrogeological maps.

An innovative approach to hydrogeological mapping based on quantitative analysis is shown in this paper. It gives some cartographical solutions for an immediate evaluation of the groundwater resources and their spatial distribution.All relevant aquifers, springs and their regime, geological and structural setting and their hydraulic role should be shown in several understandable and clear hydrogeological maps where all hydrogeological information is reported in detail in the Hydrogeological experimental Map composed by a. Hydrogeological Complexes and Natural Springs Map, b. Surface Hydrology Map, c. Conceptual Hydrogeological Model and d. Hydrogeological sections.The cartographical solutions adopted for representing all these documents are proposed in this paper. Some graphical solutions have been proposed for improving the Italian official guidelines of hydrogeological mapping at scale 1:50.000, explain the legends symbols and illustrate the structure of a hydrogeological GIS database. An application of this approach has been carried out in north-western sector of Sibillini Mts. (Marche, Italy).

Structural inheritance of pre- and syn-orogenic normal faultson the arcuate geometry of Pliocene-Quaternary thrusts:Examples from the Central and Southern Apennine Chain

n the frontal sector of the Central-Southern Apennines, surface geological data integrated with seismic line interpretation provide new constraints into the reconstruction of the structural inheritance of Mesozoic pre-orogenic and Messinian-Pliocene syn-orogenic normal faults on the salient geometry of the Pliocene-Quaternary thrust system.In the Umbria-Marche-Abruzzi area, pre-orogenic normal faults commonly juxtapose the complete Jurassic succession (about 900 metres in thickness) onto coeval condensed successions (about 50 metres in thickness) deposited over structural highs. In the Sibillini Mts and Gran Sasso area, pre-orogenic normal faults are truncated and rotated into Pliocene thrust-sheets according to simple short-cut trajectories. In particular the foreland-dipping Jurassic normal faults in the Sibillini Mts area have been rotated and reactivated during the thrust propagation forming high-angle blind-thrusts in the east verging overturned folds.The Maiella anticline, which involves the Mesozoic-Miocene Apulian carbonate succession and the related slope deposits, joins the Central Apennine fold-and-thrust system to the Apulian Chain buried below the allochthonous Units of the Southern Apennines. Seismic line interpretation allowed us to reconstruct the three-dimensional pattern of the Apulian thrusts, oriented N-S, NNW-SSE and E-W, that are parallel to normal faults related to the Pliocene-Quaternary flexural extension in the foreland. Detailed reconstruction of the Setteporte and Monte Taburno structures shows main N-S/NNE-SSW trending thrusts, branching into NW-SE/E-W trending minor thrusts and back-thrusts, characterized by push-up geometry, typically referable to a transpressive deformation and/or to the positive reactivation of normal faults. Moreover, the sharp westward deepening of the base of the Apulian sedimentary succession (from 4.5 to 6.0 sec in TWT), based on the interpretation of the CROP 11 seismic reflection profile, and the concomitant increase in thickness of the Triassic sequence along the Maiella-Casoli transect, suggest the existence of west-dipping (?)Permian-Triassic normal faults that strongly controlled the distribution and thickness variation of syn-rifting sediments. An inversion of the deepest low angle portions of the pre- and syn-orogenic normal faults is in agreement with surface data (i.e., the structural elevation of the carbonate succession in the Casoli-Bomba anticline) and seismic line interpretation (i.e., deep seated location of the base of Apulian sedimentary succession below the same anticline).In the reconstructed inversion tectonics model, the N-S trending pre-thrusting normal faults are fully inverted as N-S transpressive segments of the salient structures of the chain, whereas, the NW-SE trending thrusts inverted the low angle portion of pre-thrusting normal faults in the middle-lower crust and displaced with a short-cut the normal faults in the upper portion of the crust. As a result, the pattern of the pre-existing normal faults is inherited on the salient structures of the Central and Southern Apennine Chain.

Clay mineral assemblages and vitrinite reflectance in the Laga Basin (Central Apennines, Italy): What do they record?

AbstractTemperature-dependent clay mineral assemblages and vitrinite reflectance data have been used to investigate levels of diagenesis from the Messinian Laga Basin in the Central Apennines developed at the footwall of the Sibillini Mts. and the Gran Sasso Massif. Data are from stratigraphic units forming the main siliciclastic basin fill up to Middle Messinian gypsum-arenites and its pre-orogenic substratum. Specifically, the largest Rom% values and percentages of illite layers in illite-smectie (I-S) are found in the basin depocenter and at the footwall of the main carbonate thrust sheets. Smaller Rom% values, and percentage of illite layers in I-S characterize less subsided sectors surrounding the depocenter.The X-ray diffraction data were treated using decomposition methods and the peaks identified were rationalized in terms of discrete and/or mixed-layer phases. Complex clay mineral assemblages were found in the Laga Fm. including three sub-populations of illitic material corresponding to authigenic and detrital components. I-S mixed layers record the maximum paleotemperature the Laga Fm. experienced, which is directly related to its burial history. Kübler index (KI) data, however, suggest higher temperatures related to detrital K-micas inherited from the uplift of the Alpine-Apennines chain.A tentative calculation of paleotemperatures from selected data of organic and inorganic parameters is also proposed and compared with recent sedimentological, stratigraphic and structural data. We conclude that the Laga Basin fill never experienced temperatures of >100–110°C, generally due to variable sedimentary loading, whereas localized anomalous heating is due to the effect of the tectonic emplacement and subsequent local erosion of the Sibillini and Gran Sasso thrust sheets.

Climatic influence on slope dynamics and shoreline variations: examples from Marche region (Central Italy)

The present work aims to establish relationships between shoreline historical variations (close to the river mouths) and slope dynamics on mountain and hilly areas: these are considered as fundamental physiographic units of the Adriatic central Italy. The study deals about the deltaic system of the Chienti river, which is representative of the deltaic systems of the main Marchean rivers. Goal is to recognize possible geomorphological indicators of climatic variations during late Holocene. Debris flows on the Sibillini Mts were analysed and interpreted. Their activation can be associated with: late Pleistocene-early Holocene deglaciation, with regard to the oldest phenomena; agricultural, forestry and grazing activities during the Late Middle Ages, even though evidence of climatic conditioning is also present. Moreover, some important landslide phenomena on the high hilly areas were examined: historical data demonstrated an intense post-Middle Age activity (XVth-XVIIIth centuries) related to the strong rainfall increase as a consequence of climatic worsening.

Methods for determining the Pleistocene–Holocene component of displacement on active faults reactivating pre-Quaternary structures: examples from the Central Apennines (Italy)

In the tectonically active fault system of the Central Apennines Ridge (Italy) several normal/transtensive faults mapped as Quaternary structures show evidence of pre-Neogene thrusting activity. Therefore, determining the amount of fault-slip during Pleistocene–Holocene times is crucial for seismic hazard assessment. Three principal lines of evidence have been used in this study for estimating the pre-Quaternary activity of extensional fault systems in the Central Apennines. The first is the geological and stratigraphic record (i.e. thickness and facies variations) for pre-Quaternary successions. The second is the widespread structural analysis evidence of extensional faults involved in Neogene thrust tectonics; whether considering a passive role (e.g. fault carried and tilted above a thrust-sheet) or inversion (e.g. positive inversion and related minor structures). The third is the geomorphological evidence, particularly erosion surface analysis, which permits the understanding of the relief generated by tectonics after the formation of post-thrusting erosional surfaces. Preliminary results from some faults which belong to the Sibillini Mts. and the Norcia extensional fault zones show clear evidence of Quaternary reactivations.

Geomorphological evidence for anti-Apennine faults in the Umbro-Marchean Apennines and in the peri-Adriatic basin, Italy

The Apennines are a relatively recent mountain chain which has been affected by uplift movements since the Upper Pliocene. In fact the remnants of an “erosional surface”, reduced close to base level, is preserved at the top of the relief. There is no general agreement on the geodynamic stress field and mechanisms which are creating the chain. However, it is largely accepted that uplift occurred together with the activation, on the western side of the chain, of extensive faults, oriented in the Apennine direction (NW-SE), which have been linked to the opening of the Tyrrhenian sea. A great debate is going on about the presence and significance of anti-Apennine faults (NE-SW) which have been observed by some authors but completely denied by others. The main evidence is represented by[ (1) block faulting of the remnants of the “erosional surface”. Along the Marchean Ridge, more elevated relief, delimiting relatively depressed areas, was created in correspondence with the Sibillini Mts. and Mt. S. Vicino. Similar evidence has been found in the Umbro-Marchean Ridge. Locally more than 1500 metres of displacement have been observed between more and less uplifted remnants. (2) Block faulting of fan deltas and related beaches, of Sicilian to Crotonian age, with more elevated sediments preserved between the Tronto and Tenna rivers and between the Musone and Esino rivers. Maximum displacement along a transect parallel to the coast is 200 metres. (3) fault-scarps affecting the Middle Pleistocene river terraces, as observed along the Esino, the Tronto, the Chienti and the Tenna river valleys. Maximum displacements are in the order of 50 metres. (4) Faulting of horizontal karst galleries and reorientation of the cave network, as in the Frasassi Gorge. Maximum displacements are about 100 metres. (5) Captures and alignments in the drainage network of the main river courses. (6) Large-scale gravitational movements, as in the Ancona landslide, and along the Chienti and Esino rivers. Their activation occurred in most cases after the Lower Pleistocene and although their displacements may be of relatively limited extent, dispite their recent activity, they played a major role in the modelling of the landscape. These faults display transtensive, extensional and trascurrent movements. Apart from the controversial geodynamic significance of these faults, from a geomorphological point of view they must be considered transverse elements of the stress field from blocks more or less uplifted along the Apennine chain. The importance and timing of activity of these faults in the Quaternary geomorphological evolution of the Umbria-Marchean Apennines is demonstrated using evidence usually underestimated by structural geologists, which can contribute to a debate based on a multidisciplinary approach.

Fault‐generated mountain fronts in the central apennines (Central Italy): Geomorphological features and seismotectonic implications

AbstractThe morphotectonic framework of the Central Apennines is given by faulted blocks bounded by normal faults, mostly trending NW–SE, NNW–SSE and NE–SW, which cut previous compressive structures. Such a structural setting is consistent with the focal mechanisms of the earthquakes which often occur in this area.In this paper, three lithologically different normal fault‐generated mountain fronts are analysed in order to assess the relations between their geomorphic features and active tectonics. They border the Norcia depression (Sibillini Mts, Umbria), the Amatrice–Campotosto plateau (Laga Mts, Lazio) and the Fucino basin (Marsica Mts, Abruzzi).The Norcia depression is bounded by a N20°W trending normal fault to the east and by a parallel antithetic fault to the west. The main fault has a 1000 m throw and gives rise to a wide fault escarpment, characterized by: (1) sharp slope breaks due to low angle gravity faults; (2) important paleolandslides; and (3) several fault scarplets on the piedmont belt affecting Quaternary deposits.The Amatrice–Campotosto plateau is delimited by the western slope of Mt Gorzano which runs along a N20°W trending normal fault having a 1500m throw. Minor parallel faults dislocate Quaternary landforms. Large‐scale massmovements also occur here.The Fucino basin was struck by the 1915 Avezzano earthquake (I=XI MCS) which produced extensive surface faulting along two parallel NW trending normal fault escarpments on the eastern border of the basin. There is paleoseismic evidence including buried gravity graben in Late Glacial gravels and tectonic dip‐slip striations on Holocene calcitic crusts covering bedrock normal fault planes.These data suggest that active extensional tectonics plays a major role in the slope morphogenesis of the Central Apennines and they indicate the importance of geomorphic analysis in seismic zonation of this area.