Central-northern Apennines Research Articles

Morphological and Genomic Differences in the Italian Populations of Onopordum tauricum Willd.-A New Source of Vegetable Rennet.

Onopordum tauricum Willd., a species distributed in Eastern Europe, has been the subject of various research endeavors aimed at assessing its suitability for extracting vegetable rennet for use in the production of local cheeses as a substitute for animal-derived rennet. In Italy, the species has an extremely fragmented and localized distribution in six locations scattered across the central-northern Apennines and some areas of southern Italy. In this study, both the morphology and genetic diversity of the six known Italian populations were investigated to detect putative ecotypes. To this end, 33 morphological traits were considered for morphometric measurements, while genetic analysis was conducted on the entire genome using the ddRAD-Seq method. Both analyses revealed significant differences among the Apennine populations (SOL, COL, and VIS) and those from southern Italy (ROT, PES, and LEC). Specifically, the southern Italian populations appear to deviate significantly in some characteristics from the typical form of the species. Therefore, its attribution to O. tauricum is currently uncertain, and further genetic and morphological analyses are underway to ascertain its systematic placement within the genus Onopordum.

Pathogenic fungi and oomycetes causing dieback on Fraxinus species in the Mediterranean climate change hotspot region

Environmental changes are occurring on a global scale, but their effects are most pronounced in climate change hotspot zones, such as the Mediterranean basin. Within this area Italy, extending from its southern coasts in the core of the Mediterranean Sea to its northernmost pre-Alpine and Alpine regions, is characterized by a variety of climatic conditions and vegetation types. Surveys conducted in 2018–2022 in forest formations of Central-Northern Italy revealed that the enhanced warming trend and irregular distribution of precipitations are strongly impacting the health of Fraxinus species, with some pathogenic fungi and oomycetes being important contributing factors to the decline of the three main ash species growing there: common ash (Fraxinus excelsior), flowering ash (Fraxinus ornus), and narrow-leaved ash (Fraxinus angustifolia). Isolation from symptomatic plant material collected countrywide under different site conditions and pathogenicity tests revealed a complex phytopathological framework, with several pathogenic species in addition to Hymenoscyphus fraxineus involved with a prominent role in the ash dieback etiology. Key microbial taxa included the fungal and oomycete pathogens Botryosphaeria dothidea, Diplodia fraxini, Diplodia subglobosa, Phytophthora acerina, and Phytophthora plurivora. The disease impact was higher on sites where ash trees grew under environmental stress (i.e., areas characterized by mild dry winters, hot summers with intense and prolonged drought) and exhibited reduced vigor, also as a consequence of anthropogenic interference (i.e., silvicultural management and fires). The identified causative agents are emerging pathogens that thrive under warmer conditions, their impact in the investigated areas being prevalent compared to H. fraxineus, which appears to be restricted on the Italian peninsula to the cooler and wetter valleys of the Alps and Central-Northern Apennines.

Screening, classification, capacity estimation and reservoir modelling of potential CO2 geological storage sites in the NW Adriatic Sea, Italy

In Italy, the central-northern Apennines and Adriatic Sea domains have been identified as potential CO2 storage areas. Although capacity estimates have been undertaken at a regional scale, more detailed research is required to reduce uncertainty. The present study helps address this gap by conducting a detailed screening of a representative area in the north-western Adriatic Sea for suitable CCS sites, using an extensive dataset composed of both public and private seismic and borehole data. Work included selecting suitable sites based on proposed selection criteria, calculating their theoretical and effective storage capacities applying a probabilistic approach, and then performing dynamic flow modelling on one of the selected sites that is representative of fractured carbonate reservoirs. Based on the screening results, a total of 21 out of 38 structures were selected as having the required characteristics suitable for CO2 storage. As expected, the clastic rock reservoirs have the greatest potential capacity, although some fractured carbonate reservoirs did yield important volumes due to their dual porosity / permeability characteristics. Modelling of one such site highlighted the complex interplay between primary and secondary porosity / permeability on plume migration and capacity estimation. Our results highlight the need to integrate analytical calculations with dynamic simulations for more detailed, site-specific studies to improve the estimates of CO2 storage capacity.

Plio-Quaternary interaction between Adria and surrounding orogens: a Central-Northern Apennines perspective

Plio-Quaternary interaction between Adria and surrounding orogens: a Central-Northern Apennines perspective

Shear zone fabrics and their significance in curved, inverted basin-derived thrust systems

In this study, we report how criteria inferred from structural and kinematic analysis of shear zone fabrics can be instrumental in deciphering events of positive or negative inversion tectonics. Mesoscopic structural and kinematic analyses are performed on well-exposed brittle-ductile thrust shear zones within curved thrust systems in the Central-Northern Apennines of Italy.The structural and kinematic features of thrust-related tectonites make it possible to outline a history of positive inversion. S/C- and S-tectonites/fabrics are distinctive of frontal or oblique thrust ramps, respectively. In particular, S-fabrics result from selective transpressional-reactivation of pre-thrusting normal faults. By contrast, more complex composite fabrics, characterized by folded cleavage, reveal a history of negative inversion tectonics. Mesocopic cleavage folding is ascribed to shear-sense reversal along the shear surfaces during extensional reactivation of pre-existing thrusts; or to synthetic reactivation by listric foreland-dipping normal faults, merging downwards on former thrust surfaces during protracted episodes of gravitational collapse.Shear zone fabrics identification criteria, here illustrated from thrusts of different size, if systematically used, may be diagnostic of different deformation paths, and hence provide useful tools to elucidate the tectonic history of curved thrust systems in orogens that have experienced multiple episodes of inversion.

Along-strike variation of fault-related inversion folds within curved thrust systems: The case of the Central-Northern Apennines of Italy

The along-strike variation of fault-related inversion folds within curved thrust systems is documented by presenting cases from the Central-Northern Apennines of Italy. Fold structures are reconstructed by integrating geological field data and structural restoration of various key balanced cross-sections, which are also constrained by the detailed interpretation of panoramic views, geological field mapping, and structural analysis. The lateral variation from fault-bend to fault-propagation folding is promoted by selective reverse reactivation of precursor, mainly rift-related, normal faults preferentially located along the oblique and frontal ramps. Their space variability is identified within single curved thrust systems of three different size testifying a scale-invariant phenomenon. Fault-bend reactivation and fault-propagation shortcut folding produce a characteristic fold interference pattern at the salient apex of the curved thrust system. The transition style depends on the pattern of the inherited normal fault template and on the amount of shortening achieved in the salient zone. The modest amount of shortening resulting from fault-related inversion folding along regional curved thrust systems is consistent with a basement-involved thick-skinned thrusting style. Recognition of fault-related inversion fold styles and of their along-strike variations represents a useful predictive tool when unravelling the kinematic evolution of curved orogenic belts resulting from positive inversion. Inversion fold development modes and their diagnostic features are also important for investigations of subsurface Earth resources.

Frictional controls on the seismogenic zone: Insights from the Apenninic basement, Central Italy

Crustal seismicity is in general confined within the seismogenic layer, which is bounded at depth by processes related to the brittle-ductile transition (BDT) and in the shallow region by fault zone consolidation state and mineralogy. In the past 10-15 years, high resolution seismological and geodetic data have shown that faulting within and around the traditional seismogenic zone occurs in a large variety of slip modes. Frictional and structural heterogeneities have been invoked to explain such differences in fault slip mode and behaviour. However, an integrated and comprehensive picture remains extremely challenging because of difficulties to properly characterize fault rocks at seismogenic depths. Thus, the central-northern Apennines provide a unique opportunity because of the integration of deep-borehole stratigraphy and seismic reflection profiles with high resolution seismological data and outcrop studies. These works show that seismic sequences are limited within the sedimentary cover (depth < 9-10 km), suggesting that the underlaying basement plays a key-role in dictating the lower boundary of the seismogenic zone.Here we integrate structural data on exhumed outcrops of basement rocks with laboratory friction data to shed light on the mechanics of the Apenninic basement. Structural data highlight heterogeneous and pervasive deformation where foliated and phyllosilicate-rich rocks surround more competent quartz-rich lenses up to hundreds of meters in thickness. Phyllosilicate horizons deform predominantly by folding and foliation-parallel frictional sliding whereas quartz-rich lenses are characterized by brittle signatures represented by extensive fracturing and minor faulting. Laboratory experiments revealed that quartz-rich lithologies have relatively high friction, μ≈0.51, velocity-strengthening to neutral behaviour, and elevated healing rates. On the contrary, phyllosilicate-rich (muscovite and chlorite) lithologies show low friction, 0.23 <μ < 0.31, a marked velocity strengthening behaviour that increases with increasing sliding velocity and negligible rates of frictional healing.Our integrated approach suggests that in the Apenninic basement deformation occurs along shear zones distributed on thickness up-to several kilometres, where the frictionally stable, foliated, and phyllosilicate-rich horizons favour aseismic deformation and therefore confine the depth of major earthquake ruptures and the seismogenic zone.

Characterization of landslide dams in a sector of the central-northern Apennines (Central Italy)

The paper analyses the landslide dam phenomenon in an area of the central-northern Apennines (Italy). A census of 53 landslides was carried out, identifying the salient parameters of both the landslides and the riverbed–alluvial plain systems. Correlations between these parameters were tested, in order to characterize the phenomenon in the study area. The most interesting relationships are those that compare the volume of landslide material either with the area of the catchment subtended by the dammed section and with the width of the riverbed–alluvial plain system. The results indicate that as the width of the fluvial system increases, and the area of the river basin subtended by the natural dam increases, the volume of the landslide accumulation necessary to produce occlusion also increases. Only one case, among those examined, escapes this general rule: a landslide of small volume made a full occlusion even though a relatively large area of basin was subtended. In this specific case, landslide velocity played an important role. So, while a high ratio between the volume of the landslide and the area of the affected basin represents a predisposing condition for the occurrence of total occlusion, it is not wholly reliable. Indexes, proposed in the literature, suggesting a quantitative assessment of landslide dam hazard, fail to forecast total occlusion unequivocally. This is because of the special characteristics of each territorial area, from lithological, geomorphological and geological-structural point of views. Such indexes, when they do not lose their intrinsic reliability (as in this case), must at least be identified with, and applied to, specific and restricted territories: they cannot be generalized.

Geological and geotechnical models definition for 3rd level seismic microzonation studies in Central Italy

The 2016–2017 seismic events that struck central Italy led the Government to carry out a project to produce the third level Seismic Microzonation studies in 138 municipalities. These activities have involved many experts in different disciplines such as geology, geomorphology, geophysics, seismology and geotechnical engineering. This project represented the first opportunity to perform nationally coordinated third level Seismic Microzonation studies over a wide area in a quite short time (6 months). It provided the chance to improve methodological procedures, to test the reliability of methods and models for site response analyses and to produce a huge amount of validated data. This paper focuses on the contribution of geological disciplines and concerns: (a) the definition of the main “morphostructural domains” of the Central-Northern Apennines; (b) the creation of an archive of all the lithostratigraphic units occurring in the study area with their conversion into engineering-geological units and their distribution in the different morphostructural domains; (c) the construction of the reference geological and geotechnical models, which are essential to classify the territory into seismically homogeneous microzones and to perform the successive 1D and 2D numerical analyses of the local site response. The geophysical dataset acquired for the study allowed a first statistical characterization of the Vs values typical of the engineering-geological units identified in this study. Some examples of the recurrent geological and geotechnical models are shown to explain the complexity and variety of the geological and geomorphological features of the investigated area and to highlight the different seismostratigraphic behavior of rocks and cover terrains. The analysis of third level Seismic Microzonation data made it possible to identify recurrent subsoil models and to note the main stratigraphic and morphological control-factors of the ground motion modification in the different morphostructural domains.

The spread of no-till in conservation agriculture systems in Italy: indications for rural development policy-making

No-tillage is a farming system aiming at minimizing soil disturbance associated with the cultivation of arable crops. This technique, together with the practices of continuous soil cover and of crop rotation, also represents one of the elements of the so called Conservation agriculture, a paradigm of sustainable agriculture that is spreading in many areas of the globe. The aim of the work is to examine the spread of No-tillage in Italy analyzing the modalities of adoption and the factors that can influence it.Modalities of adoption can vary depending on whether No-tillage represents an incremental innovation within the ordinary management of the farm, or a complementary element of an alternative technological paradigm identifiable with Conservation agriculture. Factors influencing the adoption of No-tillage, widely studied in the literature, concern the characteristics of the natural environment, the structural features of the holdings (i.e. size) and also the presence of knowledge spillovers that are largely the result of spatial networks between farmers and other stakeholders.Elaborations have been first of all aimed at distinguishing the two types of modalities of adoption and subsequently at verifying the influence of the factors mentioned above, in particular through the Local Moran Index.In summary, the work describes how the diffusion of No-tillage practices can be partly ascribed to a cost saving-oriented incremental innovation process in the framework of a conventional paradigm of agriculture that mainly pertain to large size holdings. However, there is a significant number of farms where the adoption of No-tillage practices demonstrates the decision to try a more comprehensive reorganization of the way of doing agriculture, similar to the paradigm of Conservation agriculture, and in which the cognitive and relational aspects related to the aforementioned networks seem to be very important.Spatial analysis has allowed to depict two models of adaptation to the paradigm of Conservation agriculture: one is mainly concentrated in the rural areas of the central-northern Apennines, and another is located mainly in two regions of southern Italy (Puglia and Sicily).

Conductive heat flow pattern of the central-northern Apennines, Italy

We analyzed thermal data from deep oil exploration and geothermal boreholes in the 1000-7000 m depth range to unravel thermal regime beneath the central-northern Apennines chain and the surrounding sedimentary basins. We particularly selected deepest bottom hole temperatures, all recorded within the permeable carbonate Paleogene-Mesozoic formations, which represent the most widespread tectono-stratigraphic unit of the study area. The available temperatures were corrected for the drilling disturbanceand the thermal conductivity was estimated from detailed litho-stratigraphic information and by taking into account the pressure and temperature effect. The thermal resistance approach, including also the radiogenic heat production, was used to infer the terrestrial heat flow and to highlight possible advective perturbation due to groundwater circulation. Only two boreholes close to recharge areas argue for deep groundwater flow in the permeable carbonate unit, whereas most of the obtained heat-flow data may reflect the deep, undisturbed, conductive thermal regime.

BEST STRATEGY FOR THE DEVELOPMENT OF A SEISMIC PREVENTION PLAN

An effective mitigation of seismic risk in Italy can hardly be obtained without a tentative recognition of few priority zones, where the limited resources available in the short term can be concentrated. A reliable recognition of the zones where the probability of major earthquakes is highest must be carried out by a deterministic approach, exploiting the profound knowledge acquired about the present seismotectonic context in the zones involved. Some years ago, this kind of procedure led us to identify the central-northern Apennines (i.e. the zone hit by the recent major earthquakes, 2016 and 2017) as the Italian area most prone to next strong shocks. The reliability of the methodology here proposed is also supported by the fact that the implications of the adopted tectonic setting can provide plausible and coherent explanations for the spatio-temporal distribution of major earthquakes in the central Mediterranean area in the last six centuries.

The first ophthalmosaurid ichthyosaur from the Upper Jurassic of the Umbrian–Marchean Apennines (Marche, Central Italy)

AbstractThe first ophthalmosaurid ichthyosaur from the Upper Jurassic deposits of the Central–Northern Apennines (Marche, Italy) is here described for the first time. The specimen is relatively complete and is referred toGengasaurus nicosiaigen. et sp. nov. based on a unique combination of characters, including a peculiar condition of the preaxial accessory facet on the humerus. The faunal association of the ichthyosaur-bearing level indicates a late Kimmeridgian – earliest Tithonian age, and its finding contributes significantly to our knowledge of the diversity of Late Jurassic ichthyosaurs from the Western Tethys. Two shark teeth assigned to the order Hexanchiformes were also recovered in association with the ichthyosaur specimen, suggesting that scavenging of the carcass might have occurred.Gengasauruscan be referred to Ophthalmosauridae based on the reduced extracondylar area of the basioccipital, and the presence of a preaxial digit. It differs fromOphthalmosaurusspp. in several respects, including the shape of the posterior basisphenoid, the shape of the supraoccipital, the anteriorly deflected preaxial facet of the humerus, and a proximodistally shortened ulna. The new taxon actually shares diagnostic characters with both members of the two main lineages recovered in previous phylogenetic analyses, more nested within Ophthalmosauridae. The affinities ofGengasaurusto genera from both the northern and southern hemispheres also suggest that connectivity between pelagic habitats was high during the early Late Jurassic, allowing dispersal of some forms, followed by local, endemic divergence.

The thick-bedded tail of turbidite thickness distribution as a proxy for flow confinement: Examples from tertiary basins of central and northern Apennines (Italy)

This study reviews the thickness statistics of non-channelized turbidites from four tertiary basins of Central-Northern Apennines (Italy), where bed geometry and sedimentary character have been previously assessed. Though very different in terms of size and, arguably, character of feeder system, these basins share a common stratigraphic evolution consisting in transition from an early ponded to a late unconfined setting of deposition. Based on comparison of thickness subsets from diverse locations and stratigraphic heights within the studied turbidite fills, this paper seeks to answer the following questions: i) how data collection procedures and field operational constraints (e.g. measure location, outcrop quality, use of thicknesses data from single vs. multiple correlative sections, stratigraphic thickness of the study interval) can affect statistics of sample data? ii) how depositional controls of confined vs. unconfined turbidite basins can result in different thickness-frequency distributions?; and iii) is there in thickness statistics a ‘flow confinement’ signature which can be used to distinguish between confined and unconfined turbidites? Results suggest that: i) best practices of data collection are crucial to a meaningful interpretation of sample data statistics, especially in presence of stratigraphic and spatial trends of turbidite bed thickness; ii) a systematic bias against cm-thick Tcd Bouma sequence turbidites exists in sample data, which can result in the low-end tail of empirical thickness-frequency distributions to depart significantly from the actual distribution of turbidite thickness; and iii) thickness statistics of beds starting with a basal Ta/Tb Bouma division bear a coherent relationship to the transition from ponded to unconfined depositional settings, consisting in reduction of variance and mean and, consequently, parameters, or even type, of best fit model distribution. This research highlights the role of flow stripping, sediment by-pass and bed geometry in altering the initial thickness distribution of ponded turbidites and suggests how fully ponded mini-basins represent the ideal setting for further research linking turbidite thickness statistics and frequency distribution of parent flow volumes.

Investigating fault reactivation during multiple tectonic inversions through mechanical and numerical modeling: An application to the Central-Northern Apennines of Italy

Within inversion tectonic contexts, the reactivation of pre-existing discontinuities depends upon many structural, stratigraphic and mechanical factors. Among these, a fundamental aspect is represented by the orientation and attitude of pre-existing discontinuities with respect to the new stress field. The aim of this work is to evaluate the stress regimes and the mechanical conditions that controlled the reactivation of segmented pre-thrusting normal faults in the Central-Northern Apennines of Italy. These faults were involved both in positive and negative inversion tectonic events during Tertiary-Quaternary times. Mechanical (slip tendency analysis) and numerical (using COULOMB 3.3 software) models allowed us to reconstruct a 3D stress field for both inversion events and to evaluate the effect of many parameters (orientation of faults, fault dip-angle and mechanical parameters) on fault reactivation. Our results highlighted that the orientation of pre-existing faults with respect to the stress axes represents the main factor controlling inversion tectonic phenomena, where other mechanical and geometric variables exert a subordinate role. The models well reproduce the Neogene-Quaternary deformation history reconstructed from detailed geological and structural analyses for the Central-Northern Apennines of Italy and could be applied to other regions that have experienced inversion tectonic processes.

Analogue modeling of positive inversion tectonics along differently oriented pre-thrusting normal faults: An application to the Central-Northern Apennines of Italy

Inversion tectonics represent a key process in many orogens worldwide. The related mechanisms of fault reactivation and the effects of an articulated preshortening setting on thrust and fold development are still challenging questions. Modes and geometries of inversion have been the object of several analogue models. In this work, we analyzed the influence of an articulated high-angle preexisting discontinuity in the development of thrusts using sandbox modeling. The model geometry is based on the architecture of the major faults in the Central-Northern Apennines of Italy, where differently oriented Mesozoic–Cenozoic inherited extensional structures are clearly detectable and display contrasting styles of positive inversion tectonics. Quartz-sand is the analogue material adopted to model Mesozoic–Cenozoic sedimentary successions, and glass microbeads represent preexisting fault rocks. The geometry of the segmented preexisting structure is composed of two segments with the same dip (∼60°): one oblique and another orthogonal to the shortening direction. Our results show that different styles of positive inversion tectonics can coexist and that the obliquity angle between inherited structures and the shortening direction is a leading factor controlling the degree of inversion: The oblique segment of the discontinuity exhibits a complete reactivation, whereas along the orthogonal segment, shortcut is the prevalent mechanism. The oblique element, moreover, represents a cross-strike discontinuity that guides the localization and curved geometry of the thrusts, compartmentalizing the deformation. Our findings can be applied to fold-and-thrust belts characterized by the presence of cross-strike discontinuities.

Bayesian estimation for a parametric Markov Renewal model applied to seismic data

This paper presents a complete methodology for Bayesian inference on a semi-Markov process, from the elicitation of the prior distribution, to the computation of posterior summaries, including a guidance for its implementation. The inter-occurrence times (conditional on the transition between two given states) are assumed to be Weibull-distributed. We examine the elicitation of the joint prior density of the shape and scale parameters of the Weibull distributions, deriving a specific class of priors in a natural way, along with a method for the determination of hyperparameters based on “learning data” and moment existence conditions. This framework is applied to data of earthquakes of three types of severity (low, medium and high size) that occurred in the central Northern Apennines in Italy and collected by the CPTI04(2004) catalogue. Assumptions on two types of energy accumulation and release mechanisms are evaluated.

Push-up inversion structures v. fault-bend reactivation anticlines along oblique thrust ramps: examples from the Apennines fold-and-thrust belt (Italy)

The study of inversion structures in fold-and-thrust belts that originated as extensional faults is valuable for the development of geometric and kinematic models that are helpful in unravelling the structural style and for detecting structural hydrocarbon traps. We document push-up inversion structures versus fault-bend reactivation anticlines occurring along oblique thrust ramps, by examining examples of buried Apulian structures in the Central–Southern Apennines and outcropping thrust-related folds in the Central–Northern Apennines of Italy. The different geometric features between push-up inversion structures and fault-bend reactivation anticlines are functionally controlled by the mechanical characteristics of the involved sedimentary multilayer, the original architecture of the former extensional basin, and the amount of thrust displacement. The recognition of such inversion structures is important in understanding the anatomy and structural style of foreland fold-and-thrust belts. In addition, their identification is critical in interpreting the geometry and types of structural traps that may be expected along oblique thrust ramps. This study reveals that push-up inversion structures and fault-bend reactivation anticlines could coexist along oblique thrust ramps within a curved thrust system and may be detected among analogous foreland thrust belts that include inherited extensional basins.

Seismic potential in Italy from integration and comparison of seismic and geodetic strain rates

Abstract Seismological and geodetic data provide key information about the kinematics and active tectonics of plate margins. Focal solutions enable the determining of the directions in which the current tectonic stress acts when fault rupturing occurs; GPS measurements provide information on the crustal velocity field and on current interseismic strain rates. The comparison of the strain rates resulting from the two datasets provides further insight into how large an area is affected by aseismic deformation, which is a valuable indicator for seismic hazard mitigation and estimation of the seismic potential. In this work, we investigate both seismic and geodetic strain rates and the combined field resulting from the joint inversion of the geodetic and seismic datasets, providing a picture of the overall deformation field and its variation during the last decades. In this way, we try to give an overview of the seismic potential distribution across the Apennines and southern Italy, as a qualitative analysis of space-time variations in the released seismic strain rate, compared to the space-time distribution of the cumulated geodetic strain rate. The results show a variable distribution of the seismic efficiency over Italy. The Southern Apennines shows the greatest seismic potential, highlighting a significantly lower seismicity in the last two decades over an area affected by the highest total strain rates. The Messina Straits and eastern Sicily have a significant seismic potential, together with the Calabrian arc (from the Tindari–Letojanni and central Aeolian islands to the Mt. Pollino area), as a result of seismic gaps with respect to the combined strain rates in the investigated period. This long gap highlights the longer recurrence periods for the strongest earthquakes on this area. The central–northern Apennines and off-shore northern Sicily, show a lower seismic potential than central–southern Apennines, probably due to the more recent seismicity affecting these areas.

SEISMIC HAZARD IN TUSCANY: WHICH BEST DEFENCE STRATEGY?

The hypothesis that the probability of major earthquakes in a given zone is strongly influenced by the space-time distribution of previous seismic events in the surrounding area is supported by numerous and significant pieces of evidence. This work describes a particularly clear example of this phenomenon that occurred in the central-northern Apennines during the period 1915-1920. The fact that the strong 1915 Fucino earthquake in the central Apennines was followed by an exceptional seismic reaction of the northern Apennines (6 events of magnitude greater than 5.5 in the 1916-1920 time interval) is consistent with the active tectonic setting of these zones. Furthermore, it can be demonstrated that the time occurrence of each event in the northern Apennines is compatible with the arrival of the highest values of the perturbation induced by the previous shocks, as computed by numerical modelling of postseismic relaxation.