Apenninic Belt Research Articles

Lateral variations in tectonic style across cross-strike discontinuities: an example from the Central Apennines belt (Italy)

In foreland thrust belts, abrupt lateral changes in tectonic style, structural–stratigraphic features, and topography usually occur across cross-strike faults. The Central Apennines of Italy offer an exceptional scenario of lateral variations in tectonic setting. Here, the Sangro Volturno oblique thrust ramp (SVOTR) represents the outer thrust front of the Pliocene–Quaternary foreland thrust system, confining southward the axial culmination of the orogen that occurs in the Central Apennines. We present an interpretation of the Pliocene–Quaternary evolution of this cross-strike fault through an integrated dataset including structural-geological mapping and subsurface onshore seismic reflection profiles. The interpretation of the structural framework is augmented by the analysis of low-temperature thermochronometers from 32 new sites extending across the subsurface transverse structure. As evidenced by seismic line interpretation, the localization and development of the SVOTR have been influenced by inherited extensional faults within a positive inversion tectonics context. The regional distribution of the maximum paleotemperature values across the SVOTR constrains the original extent of the allochthonous thrust sheet over all its hanging-wall and footwall blocks. The Pliocene–Quaternary thrusting and inversion of SVOTR caused the strong hanging-wall uplift, which brought to the complete erosion of the allochthonous units and the exhumation of the Adria units. The integrated analysis of low-temperature thermochronometers and structural evidence as applied in the study case can define the role of major cross-strike discontinuities in foreland thrust belts, by constraining and verifying their tectonics inversion significance and the amount of related exhumation.

Late Pleistocene differential uplift inferred from the analysis of fluvial terraces (southern Apennines, Italy)

The stratigraphic architecture and morphological assemblage of the Pleistocene fluvial terraces contained in two contiguous fluvial valleys are used to understand the spatial distribution and the timing of the differential uplift that affected two different geological and geomorphological settings of an active orogen. The study areas, both placed in the eastern sector of the southern Apennines of Italy, are the Sant'Arcangelo sedimentary basin and the Valsinni Ridge anticline. Pleistocene uplift rate of 0.7–0.9mmy−1 and historical earthquakes affecting those areas suggest active tectonics. Based on the synthem units used to classify the fluvial deposits in the field, several strath, fill, and fill-cut terraces have been mapped in the middle valleys of the Agri and Sinni rivers. Four Middle Pleistocene high terraces (Qes) are found in the Sant'Arcangelo Basin and cut its infill, and three Late Pleistocene low terraces (Qt) are found at both the Agri and Sinni valley flanks. The Agri and Sinni rivers cross-cut the NW–SE-oriented fold-and-thrust belt of the southern Apennines from W to E, producing a transverse drainage. As a result, ten- to hundred-metre deep gorges and wide floodplains were created in the middle reach of the river valleys. Computation of the bedrock incision rates from the Qes1, Qes4, and SQt1 terraces, corresponding to 1.2±0.2mmy−1 at 400–240ka and 0.8±0.2mmy−1 in the last 240ka, together with the terrace profile arrangements in the Agri and Sinni valleys, allow for the documentation of i) the differential uplift of the study area and ii) the age of terrace abandonment corresponding to the beginning age of the vertical incision in the valley floor sediments to form the Qt terraces. The differential uplift is subsequently discussed in a space and time–sequence evolution of the Late Pleistocene to assess the complex morphotectonic development that occurred in the eastern threshold of the basin. The differential uplift of both the Sant'Arcangelo Basin and Valsinni Ridge would appear to indicate that buried fold-and-thrust structures that affect the Mesozoic–Cenozoic sedimentary nappes are still active, and they also controlled the slab retreat processes in the Mediterranean region during the Late Pleistocene.

Continental delamination and mantle dynamics drive topography, extension and fluid discharge in the Apennines

The Apennines belt of Italy undergoes a northeast-trending extension at a rate of a few millimeters per year that generates moderate to large normal-faulting earthquakes. In this paper, we show that seismicity, large earthquakes, strong gas emission, and belt topography all correlate with a broad, low Vp anomaly in the uppermost mantle. We propose that a thermal/fluid anomaly in the mantle, associated with sub-lithospheric mantle replacement after delamination of the Adria lithosphere, supports the topography of the belt and drives the extensional tectonics. The mantle anomaly is likely caused by deep fluids coming from the dehydration of the material subducted during the Europe-Adria collision and the delamination of Adria. Beneath the belt, CO 2 -rich fluids are accumulated and occasionally discharged during large normal faulting earthquakes. After the replacement of sub-lithospheric mantle, the temperature at the base of the crust increases causing crustal stretching, anatexis, and strong degassing.

Interaction of seismic sources in the Apennine belt

By analyzing the historical seismicity of the Apennines since AD 1000, we have identified four major seismic sequences occurred from 1349 to 1353, 1456 to 1461, 1688 to 1706 and 1915 to 1920. Each of these crises is characterized by several strong earthquakes and by the fact that seismic activity progressively migrated from the Southern to northern Apennines. In order to provide a plausible explanation for this phenomenology, we have elaborated a detailed seismotectonic model of the Apennines, compatible with the implications of plate tectonics in the central Mediterranean region. In our model, the seismic motion of a tectonic block, induced by tectonic forces, stresses the surrounding blocks eventually causing further earthquake activity. The temporal delay between the triggering shock and subsequent strong earthquakes depends on the rheological properties of the crust–mantle system, that control post-seismic strain and stress perturbations. We argue that the spatio-temporal distribution of major earthquakes which have occurred in the Apennine belt during the most intense seismic crises since AD 1300 is consistent with the short-term implications of the ongoing tectonic setting in the central Mediterranean area and with the expected effects of post-seismic relaxation, quantified by numerical experiments based on the stress diffusion model. The results obtained point out an agreement between earthquake occurrence and the arrival of the predicted maximum amplitude of post-seismic strain and strain rate perturbation in the relevant seismic zones. Moreover, in most cases the strain regime induced by post-seismic perturbation may be compatible with the geometry and kinematics of fault systems recognized in the zones considered. These results might delineate an important tool for recognizing the zones most prone to next strong earthquakes in the study area.

Analysis of the Low-Energy Seismic Activity in the Southern Apulia (Italy)

In this paper we analysed the historical and instrumental seismicity of the seismic district “Penisola Salentina” (Salento peninsula) in the southern part of the Apuliaregion, making use of the most recent seismological database. Relocation of available dataset points out that the events are spatially distributed over a belt of deformation that approximately corresponds to Soglia Messapica (Taranto-Brindisi depression). Besides, computed source characteristics indicate dextral strike-slip solutions with an approximately E-W orientation that seismologically confirm previous geodynamic studies indicating a NE-SW extension in the Taranto-Brindisi depression. In particular, the tensional stress associated to the present seismic activity could be the consequence of the relaxation of the buckling process following the extensional re-arrangement of the Apenninic belt masses. Moreover attenuation QPvalues obtained in this study are much greater than those inferred in other parts of Italian peninsula; this result agrees with previous macroseismic investigations and indicates a greater efficiency of the studied area in the transmission of body waves.

Late Miocene–Middle Pleistocene sequences in the Po Plain – Northern Adriatic Sea (Italy): The stratigraphic record of modification phases affecting a complex foreland basin

During the Late Miocene–Pleistocene interval, a complex system of elongate foredeeps, the Po Plain-Adriatic Foredeep (PPAF), developed in the eastern sector of the Po Plain and in the northern Adriatic Sea, This system is the largest Late Miocene–Pleistocene complex of foredeep depocenters of the Periadriatic Basin with an overall length of 500 km and a width of 80–120 km.In the last 15 years, several Eni-Agip multidisciplinary studies analyzed the buried Late Miocene–Pleistocene succession of the central-eastern Po Plain and northern Adriatic Sea. Detailed revisions of biostratigraphy, chronostratigraphy, sedimentology, seismic interpretation and sequence stratigraphy were performed using the very large Eni subsurface dataset including over 500 deep exploration and development wells and regional 2D and 3D seismic surveys. The large availability of subsurface data, the preservation and the relatively moderate structural deformation of the studied succession were essential factors for the generation of a detailed three-dimensional geological model for the foredeep basins and also for the related ramp/foreland and thrust-top basins areas. The model, which is presented in this paper, may be considered, for the large volume of qualitative and quantitative information, as a reference model for tectonically active foredeep basins dominated by basin-scale sand-rich turbidite systems.During the Late Miocene, Pliocene and Early Pleistocene a severe tectonic activity affected the northern Apennine and the PPAF area. Due to the northern Apennine compressive tectonics, the PPAF underwent four regional phases of compressional deformation and depocenter migration towards the foreland (to the northeast). During these tectonic phases, four basin-scale tectonic unconformities were generated: the Latest Tortonian, the Intra-Messinian, the Intra-Zanclean and the Gelasian Unconformities.The sequence-stratigraphic analysis of the basin was based on the recognition of allogroups, i.e. major stratigraphic units bounded at base and top by the four regional tectonically-induced unconformities, and of their component sequences, mainly of tectonic origin, ranked on the basis of their physical scale.During the latest Miocene-to-Pleistocene time interval the foredeep shape was affected by a large variability in space through time, ranging from regular elongated shape to irregular shape, from simple foredeep to fragmented foredeep. A new evolutive model for the Apennine foredeep with two evolutive stages is proposed in this paper.The PPAF was a deep-marine basin with water depths usually exceeding 1000 m. Its latest Miocene–Pleistocene succession mainly consists of thick sequences of turbidite deposits. Basin-scale, sand-rich, highly-efficient turbidite systems were largely predominant in the foredeep. Thick-bedded sand/sandstone lobes and thin-bedded fine-grained turbidite basin plain deposits represent the most common turbidite facies associations. Paleocurrents are predominantly directed to the southeast, parallel to the foredeep main axis.The thick PPAF succession consists of the turbidites of the Bagnolo (latest Tortonian–syn-evaporitic Messinian), Fusignano (post-evaporitic Messinian), Canopo (latest Messinian–Zanclean), Porto Corsini (Zanclean–Piacentian), Porto Garibaldi (Piacentian–Calabrian) and Carola (Calabrian–Late Pleistocene) Formations.The fluvio-deltaic systems of the Paleo-Adda, Paleo-Mincio and Paleo-Adige Rivers, located along the Alps margins of Lombardia and Veneto foreland, provided the bulk of the PPAF siliciclastic sedimentary input. With the partial exception of the post-evaporitic Messinian, the clastic supply from the northern Apennine belt was subordinate.The Messinian depositional systems underwent dramatic changes due to the combination of the salinity crisis and Intra-Messinian morphostructural reshaping. This behavior was not associated with a unique, dramatic lowering related to the Messinian Salinity Crisis (MSC) but was modulated by a combination of factors like climatic changes, deformation phases, isostatic rebound and sediment flux.Stratigraphic relationships among decompacted coastal wedges suggest that the total lowering of the relative base-level did not exceed 900 m in the study area. This total drop was reached through three distinct base-level changes probably related to evaporation (ME2 Sequence), differential subsidence (ME3 Sequence) and regional uplift possibly associated to isostatic rebound (ME4 Sequence). The Zanclean (Early Pliocene) relative sea-level rise is estimated on the order of 800–900 m, with a shoreline landward shift in the foreland of at least 70 km. In the study area, the MSC was therefore recorded by an overall strongly asymmetric cycle where discrete events of various origin punctuated a relatively gradual base-level fall. During the entire MSC, the PPAF depocenters remained in relatively deep-water or deep-water conditions, associated with turbiditic sedimentation and locally to bottom currents.

Fluid pressure, stress field and propagation style of coalescing thrusts from the analysis of the 20 May 2012 ML 5.9 Emilia earthquake (Northern Apennines, Italy)

Terra Nova, 25, 72–78, 2013AbstractTwo major earthquakes of ML 5.9 and 5.8 and hundreds of aftershocks affected the Emilia region (Po Plain, Italy) between 20 May and June 2012. The events concentrate in the uppermost 10 km of the crust with few events up to 30 km. Two buried, sub‐parallel N100°E striking thrusts of the Northern Apennines belt are reactivated. These thrusts coalesce at the interface between the metamorphic basement of the belt and the overlying, about 10‐km thick, sedimentary succession. Focal mechanisms indicate a compressive stress field with a sub‐horizontal, roughly N‐S striking σ1. This stress field is consistent with active shortening in Northern Apennines. Suprahydrostatic pore pressure and σ1 ∼ σ2≠σ3 are required to reactivate the thrusts. The involved fluids could be gas and brines hosted in the folded sedimentary successions. The time and spatial evolution of the seismicity indicates a foreland to hinterland propagation of the ruptures and a thin‐skinned deformation of Northern Apennines.

Orchis × colemanii hybridization: Molecular and morphological evidence, seed set success, and evolutionary importance

Despite highly specialized pollination strategies, hybridization is a common phenomenon among Mediterranean deceptive orchids. Food-deceptive species sire a progeny of F1 unfertile plants, which work as a late post-zygotic barrier. Conversely, when pre-zygotic barriers of sexually deceptive (Ophrys) species are absent, the hybrids are fertile and an extensive introgression may occur. Here, we have performed molecular analysis and hand pollination treatments to characterize a hybrid zone of two food-deceptive species, O. mascula and O pauciflora. Hybrids (called O.×colemanii) have shown different amounts of parental nrDNA, strongly supporting that they are F2 and/or successive hybrid generations. Comparable high levels of reproductive success have been detected in natural conditions and in experimental crosses suggesting the absence of effective reproductive barriers either between hybrids, either between hybrids and parental species. In light of ecological and distributional features of O.×colemanii across its distribution range, we hypothesize that these populations have originated by secondary contact in the periglacial belt of Apennines. Moreover, the rare and localized O. pauciflora could benefit a genetic enrichment by hybridizing with a widespread related species. O.×colemanii is not a dead end population, but may have a role as potential reserve of adaptive variability and is an unusual stage along the speciation process.

Post-seismic relaxation: An example of earthquake triggering in the Apennine belt (1915–1920)

The strong earthquake (M=7) that occurred in the Fucino basin (central Italy) on January 13, 1915 was followed by six earthquakes of M>5.5 and several other shocks of M>5 in the major seismic zones of the northern Apennines from 1916 to 1920. This seismicity pattern is consistent with the implications of the present tectonic setting in the study area, which suggests that strong decoupling earthquakes in the central Apennines cause a significant increase of tectonic load, and possibly of seismicity, in the northern Apennines. A numerical simulation, carried out by an elastic-viscous model, of the stress diffusion induced by the Fucino and successive largest earthquakes, shows that each of the above shocks occurred when the respective zone was reached by the highest values of the strain and strain rate perturbation triggered by the previous events. Furthermore, the computed strain regime at each earthquake site is consistent with the known faulting pattern. The results provide important insights into the physical mechanism that controls the interaction of seismic sources in the central and northern Apennines.

The Italian present-day stress map

SUMMARY In this paper, we present a significant update of the Italian present-day stress data compilation not only to improve the knowledge on the tectonic setting of the region or to constrain future geodynamic models, but also to understand the mechanics of processes linked to faulting and earthquakes. In this paper, we have analysed, revised and collected new contemporary stress data from borehole breakouts and we have assembled earthquake and fault data. In total, 206 new quality-ranked entries complete the definition of the horizontal stress orientation and tectonic regime in some areas, and bring new information mainly in Sicily and along the Apenninic belt. Now the global Italian data set consists of 715 data points, including 499 of A–Cquality,representinganincreaseof37percentcomparedtothepreviouscompilation.The alignment of horizontal stresses measured in some regions, closely matches the ∼N–S firstorder stress field orientation of ongoing relative crustal motions between Eurasia and Africa plates. The Apenninic belt shows a diffuse extensional stress regime indicating a ∼NE–SW direction of extension, that we interpret as related to a second-order stress field. The horizontal stress rotations observed in peculiar areas reflect a complex interaction between first-order stress field and local effects revealing the importance of the tectonic structure orientations. In particular, in Sicily the new data delineate a more complete tectonic picture evidencing adjacent areas characterized by distinct stress regime: northern offshore of Sicily and in the Hyblean plateau the alignment of horizontal stresses is consistent with the crustal motions, whereas different directions have been observed along the belt and foredeep.

The Pliocene‐Quaternary wedge‐top basins of southern Italy: an expression of propagating lateral slab tear beneath the Apennines

AbstractIn recent years, contrasting seismic tomographic images have given rise to an extensive debate about the occurrence and implications of migrating slab detachment beneath southern Italy. One of the most pertinent aspects of this process is the concentration of the slab pull force, and particularly its surface expression in terms of vertical motions and related basin subsidence/uplift. In this study we focused on shallow‐water to continental, Pliocene‐Quaternary basins that formed on top of the Apennine allochthonous wedge after its emplacement onto a large foreland carbonate platform domain (Apulian Platform). Due to the thick‐skinned style of deformation controlling the Pliocene‐Pleistocene stages of continental shortening, a high degree of coupling with the downgoing plate appears to characterize the late tectonic evolution of the southern Apennines. Therefore, the wedge‐top basins analysed in this study, although occurring on the deformed edge of the overriding plate, are capable of recording deep geodynamic processes affecting the slab. Detailed stratigraphic work on these wedge‐top basins points to a progressive SE‐ward migration of basin subsidence from c. 4 to c. 2.8 Ma over a distance of about 140 km along the strike of the Apennine belt. Such a migration is consistent with a redistribution of slab‐pull forces associated with the progressive lateral migration at a mean rate in the range of 12–14 cm y–1 of a slab tear within the down‐going Adriatic lithosphere. These results yield fundamental information on the rates of first‐order geodynamic processes affecting the slab, and on related surface response.

Evidence of large scale deformation patterns from GPS data in the Italian subduction boundary

We present the velocity field in Italy derived from over 300 continuous GPS stations operated in the 1998–2009 time span. The GPS network maps the whole country with a mean inter-site distance of about 50 km and provides a valuable source of data to study the ongoing deformation processes in the central Mediterranean. The estimated horizontal and vertical velocity fields show major significant features and also less known second-order kinematic features. A general uplift characterizes the whole Apennines and Alpine belts that follow the topographic ridge, whereas the Po Plain shows a gradually increasing subsidence from west to east. The Apennines belt displays a distinctive extension (50–80 10 − 9 yr − 1 ) while compressive tectonic regimes characterize northern Sicily, eastern Alps and the northeast front of the northern Apennines (25–50 10 − 9 yr − 1 ). Second-order deformation patterns, on large scale wavelength (~ 100 km) have been detected on the accretionary prism of central and southern Apennines that are highly correlated with other geophysical data (Vp anomalies, seismic anisotropy, etc.) and related to deep rooted sections (70–100 km), marked by different subduction regimes. Apparently at this scale-length the observed deformations are governed by the lithosphere as a whole. We interpret these deformations as a result of different subduction mechanisms, such as variations of the subduction rollback velocity affecting different segments of the subduction zone and/or to mantle flows in proximity of the slab edges. Further south, in central-southern Sicily, we detect a contraction of (− 1.1 ± 0.2) mm/yr that probably accommodates part of the Africa–Eurasia convergence on the outer thrust front of the Apennines–Maghrebides belt. This hypothesis agrees with an independent analysis of the seismicity associated to the Sicilian Basal Thrust, thought to be still active. The ITRF2005 estimates of the new GPS velocity field are available also in SINEX format as supplementary file S1.

The geochemical signature caused by earthquake propagation in carbonate-hosted faults

Friction laboratory experiments have been performed at sub-seismic (≈ 0.01 m/s) to seismic slip rates (> 1 m/s) on dolomite gouges of the Triassic evaporites, which hosted the five mainshocks (5 < M w < 6) of the 1997 Colfiorito earthquakes in the Northern Apennines (Italy). Experimental faults are lubricated as marked falls of the steady state sliding friction coefficients, μ ss ≈ 0.2, are observed at seismic slip rates, as opposed to values of μ ss ≥ 0.6 attained for sub-seismic slip rates. At seismic slip rates decarbonation reactions, triggered by frictional heating in the experimental slip zone, produced: 1) new fluid (CO 2) and mineral phases (e.g. Mg-calcite, periclase/brucite, lime/portlandite); 2) isotopic fractionation between the reaction products and the reactant mineral phases. The variations of total dissolved inorganic carbon (TIDC) in concentration Δ(TDIC) and isotopic composition Δ(δ 13 C TIDC) in a carbonate aquifer, with geochemical parameters similar to those of an aquifer located in the seismic belt of the Northern Apennines, have been modelled after an input of earthquake-produced CO 2. Modelling results show that variation in Δ(δ 13 C TIDC) can be detected in volumes of groundwater which are about three times larger than those calculated for the variations in Δ(TDIC). For amounts of CO 2 produced by coseismic decarbonation of ≤ 5 wt.% of the slip zone gouge, modelling results show that a detectable geochemical anomaly is obtained if the produced CO 2 is dissolved into volumes of water comparable to those of the shallower aquifers feeding the springs in the 1997 Colfiorito earthquakes area. We conclude that the integration of results from laboratory experiments, performed at seismic condition, and geochemical analyses can potentially aid in the calibration of monitoring strategies of geochemical properties of water in seismically active areas and provide insights into seismic fault zone processes (e.g. constraints on the temperature rise during earthquake propagation).

Upper crustal structure, seismicity and pore pressure variations in an extensional seismic belt through 3-D and 4-D VPand VP/VSmodels: The example of the Val d'Agri area (southern Italy)

[1] We use local earthquake tomography and background seismicity to investigate static and transient features of the crustal velocity structure in the Val d'Agri (southern Apennines, Italy), one of the regions in central Mediterranean with the highest seismogenic potential. The upper crust is dominated by two broad high-velocity anticlines of the buried Apulia Carbonate Platform ramping on two parallel high-angle thrusts interpreted as preexisting inverted normal faults. The deep core of the anticlines consists of very high VP (up to 6.9 km/s) and low VP/VS rocks, suggesting the involvement of the Apulian crystalline basement in the Apennine belt. These results provide valuable constraints on the Apennine belt tectonic evolution, supporting a thick-skinned interpretation for the Pliocene terminal phase of the compressional tectonics. The geometry of the Val d'Agri Quaternary basin is controlled by these inherited compressive features, whereas the presently active extensional tectonics barely reworked the structure. We find inconsistency between the structure of the Apulia Carbonate Platform and the location and geometry of the Quaternary normal faults mapped at the surface. This suggests either the immaturity of the normal faults or their secondary role in accommodating the extension. We observe spatiotemporal (4-D) changes of VP and VP/VS models defining transient variations of pore fluid pressure in the upper crust. A strong change in the VP/VS ratio heralds a raise in the seismicity rate that can be related to large water level changes in a nearby artificial lake. This evidence is consistent with a mechanism of reservoir-induced seismicity by fluid pressure increase and pore pressure diffusion. The 4-D velocity variations are confined in the shallow portion of the upper crust (3–6 km depth) where fluids are stored in a highly fractured medium. Pore pressure fluctuations can affect the strength of fault segments, favoring seismicity rate changes along the active faults and possibly promoting large future earthquakes.

Evidence for localized active extension in the central Apennines (Italy) from global positioning system observations

To assess how contemporary crustal extension is accommodated in the central Apennines, we use a new continuous and survey-style global positioning system velocity solution and model the velocity field using a bicubic spline interpolation method. The partitioning of contemporary deformation over the ∼100-km-wide central Apennines belt reveals a pattern of strain accumulation that largely reflects the spatial distribution of historic and recent seismicity. The highest gradients of horizontal velocities are observed across those faults associated with M > 6 historical earthquakes. Dislocation modeling shows that interseismic elastic loading, in which creep occurs below the seismogenic upper crust on the downdip extensions of historically active faults, reproduces the observed velocity gradients. The current resolution level of Quaternary fault slip rates estimates hinders the comparison with past deformation patterns and, in particular, the discrimination between (1) migrating episodes of short-term focused activity, (2) a distributed pattern of simultaneous deformation on parallel fault systems, or (3) long-term localization of active extension. Taking into account geomorphological evidence, we propose that the geodetically observed deformation spatially corresponds with a long-term localization of strain along the long-wavelength (>100 km) topographic bulge caused by its highest gravitation potential energy relative to surrounding lowlands.

Determining rheology from deformation data: The case of central Italy

The study of geodynamics relies on an understanding of the strength of the lithosphere. However, our knowledge of kilometer‐scale rheology has generally been obtained from centimeter‐sized laboratory samples or from microstructural studies of naturally deformed rocks. In this study, we present a method that allows rheological examination at a larger scale. Utilizing forward numerical modeling, we simulated lithospheric deformation as a function of heat flow and rheological parameters and computed several testable predictions including horizontal velocities, stress directions, and the tectonic regime. To select the best solutions, we compared the model predictions with experimental data. We applied this method in Italy and found that the rheology shows significant variations at small distances. The strength ranged from 0.6 ± 0.2 TN/m within the Apennines belt to 21 ± 6 TN/m in the external Adriatic thrust. These strength values correspond to an aseismic mantle in the upper plate and to a strong mantle within the Adriatic lithosphere. With respect to the internal thrust, we found that strike‐slip or transpressive, but not compressive, earthquakes can occur along the deeper portion of the thrust. The differences in the lithospheric strength are greater than our estimated uncertainties and occur across the Adriatic subduction margin. Using the proposed method, the lithospheric strength can be also determined when information at depth is scarce but sufficient surface data are available.

Seismic interpretation of the Laga basin; constraints on the structural setting and kinematics of the Central Apennines

Abstract: The Messinian Laga basin is the largest foreland basin within the Central Apennines fold and thrust belt (Italy). This area, actively investigated in the 1980s and 1990s for hydrocarbon resources, is considered a valuable analogue for clastic reservoirs developed in confined structural settings. Furthermore, it represents a key area for understanding the evolution of the Apennines, as it links the internal, structurally uplifted Early Miocene fold and thrust belt of the western Central Apennines with the more external and recent belt to the east. Despite several papers published on this area, the only reconstruction of the substratum structure is an internal and classified industry report. During the present study, we had access to a seismic database comprising 200 km of seismic profiles that were collected between 1983 and 1990. These data allowed us to reconstruct the structural setting of the Laga basin substratum, define the lateral continuity of the main compressional structures within the basin, construct a balanced cross-section, and define the shortening values.

Very slightly anomalous leakage of CO2, CH4 and radon along the main activated faults of the strong L’Aquila earthquake (Magnitude 6.3, Italy). Implications for risk assessment monitoring tools &amp; public acceptance of CO2 and CH4 underground storage

Abstract The 2009-2010 L’Aquila seismic sequence is still slightly occurring along the central Apenninic Belt (August 2010), spanning more than one year period. The main- shock (Mw 6.3) occurred on April 6th at 1:32 (UTC). The earthquake was destructive and caused among 300 casualties. The hypocenter has been located at 42.35 °N, 13.38° at a depth of around 10 km. The main shock was preceded by a long seismic sequence starting several months before (i.e., March, 30, 2009 with Mw 4.1; April, 5 with Mw 3.9 and Mw 3.5, a few hours before the main shock). A lot of evidences stress the role of deep fluids pore-pressure evolution–possibly CO2 or brines - as occurred in the past, along seismically activated segments in Apennines. Our geochemical group started to survey the seismically activated area soon after the main-shock, by sampling around 1000 soil gas points and around 80 groundwater points (springs and wells, sampled on monthly basis still ongoing), to help in understanding the activated fault segments geometry and behaviour, as well as leakage patterns at surface (CO2, CH4, Radon and other geogas as He, H2, N2, H2S, O2, etc …), in the main sector of the activated seismic sequence, not far from a deep natural CO2 reservoir underground (termomethamorphic CO2 from carbonate diagenesis), degassing at surface only over the Cotilia-Canetra area, 20 km NW from the seismically activated area. The work highlighted that geochemical measurements on soils are very powerful to discriminate the activated seismogenic segments at surface, their jointing belt, as well as co-seismic depocenter of deformation. Mostly where the measured “threshold” magnitude of earthquakes (around 6), involve that the superficial effects could be absent or masked, our geochemical method demonstrated to be strategic, and we wish to use these methods in CO2 analogues/ CO2 reservoir studies abroad, after done in Weyburn. The highlighted geochemical - slight but clear anomalies are, in any case, not dangerous for the human health and keep away the fear around the CO2–CH4 bursts or explosions during strong earthquakes, as the L’Aquila one, when these gases are stored naturally/industrially underground in the vicinity (1–2 km deep). These findings are not new for these kind of Italian seismically activated faults and are very useful for the CO2–CH4 geological storage public acceptance: Not necessarily (rarely or never) these geogas escape abruptly from underground along strongly activated faults.

Control of the 2009 L'Aquila earthquake, central Italy, by a high‐velocity structure: A receiver function study

Receiver functions (RFs) analyzed at two permanent broadband seismic stations operating in the epicentral area of the Mw 6.3, 2009 L'Aquila earthquake (central Italy) yield insight on crustal structure along the fault rupture. The harmonic decomposition of RFs highlights a subsurface structure in which both isotropic and anisotropic features are present. We model the waveforms using recently developed Monte Carlo methods. The retrieved models display a common depth structure, between 10 and 40 km depth, consistent with the under‐thrusting of the Adria lithosphere underneath the Apennines belt. Along the fault, in the uppermost crust, the S wave velocity structure is laterally heterogeneous. Right above the hypocenter, we find a 4–6 km thick, very high S wave velocity body (Vs as high as 4.2 km/s) that is absent in the SE portion of the fault, where the earthquake propagated. The high‐Vs body is coincident with the area of fewer aftershocks and is anticorrelated with the maximum slip patches of the earthquake, as modeled by differential interferometric synthetic aperture radar (DInSAR) and strong motion data. We interpret this high‐Vs body as a high‐strength barrier responsible for the high peak ground motion in the near field, observed in the L'Aquila city and surroundings, and for the complexity in the rupture evolution. The retrieved seismic S wave velocity of this body far exceeds common Vs values in the upper crust and it is more compatible with values observed in mafic basement rocks.

Present-day stress in the surroundings of 2009 L’Aquila seismic sequence (Italy)

SUMMARY The axial zone of the Apenninic belt in central Italy is a tectonically active region affected by post-orogenic Quaternary extension. The present-day stress field is characterized by a minimum horizontal stress (Shmin) ∼ NE–SW oriented, derived mainly from earthquake focal mechanisms and secondarily from borehole breakouts and fault data. The paper describes the computation of the Shmin orientation along two deep boreholes located in the vicinity of the area hit by the 2009 April 6, Mw 6.3 L’Aquila earthquake. The analysed wells show breakout zones at a depth range between 1.4 and 4.6 km, giving precious information on a depth interval usually not investigated by any other data. The results show an Shmin N81 ± 22° and N74 ± 10° oriented for Varoni 1 and Campotosto 1 wells, respectively. The comparison among the breakouts, the 2009 seismic sequence, the past seismicity and the Quaternary faults indicates a small rotation of Shmin orientation from ∼ NE, in the southern, to ∼ ENE in the northern sector of the study area, where the wells are located. These differences are linked both to the natural variations of data and to the orientation of the main tectonic structures varying from NW–SE in the Abruzzi region to ∼ N–S moving toward the Umbro-Marchean Apennines. The identification of constant Shmin orientations with depth derived from all the examined active stress data, confirms the breakouts as reliable stress indicators also for aseismic areas.