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We investigated the spatial relationships among 18 known seismogenic faults and 1651 wells drilled for gas exploitation in the main hydrocarbon province of northern-central Italy, a unique dataset worldwide. We adopted a GIS approach and a robust statistical technique, and found a significant anticorrelation between the location of productive wells and of the considered seismogenic faults, which are often overlain or encircled by unproductive wells. Our observations suggest that (a) earthquake ruptures encompassing much of the upper crust may cause gas to be lost to the atmosphere over geological time, and that (b) reservoirs underlain by smaller or aseismic faults are more likely to be intact. These findings, which are of inherently global relevance, have crucial implications for future hydrocarbon exploitation, for assessing the seismic–aseismic behaviour of large reverse faults, and for the public acceptance of underground energy and CO2 storage facilities—a pillar of future low carbon energy systems—in tectonically active areas.

We adopted a multidisciplinary approach to investigate the seismotectonic scenario of the 30 October 2016, Mw 6.5, Norcia earthquake, the largest shock of the 2016–2017 central Italy earthquake sequence. First, we used seismological and geodetic data to infer the dip of the main slip patch of the seismogenic fault that turned out to be rather low‐angle (~37°). To evaluate whether this is an acceptable dip for the main seismogenic source, we modeled earthquake deformation using single‐ and multiple‐fault models deduced from aftershock pattern analyses. These models show that the coseismic deformation generated by the Norcia earthquake is coherent with slip along a rather shallow‐dipping plane. To understand the geological significance of this solution, we reconstructed the subsurface architecture of the epicentral area. As the available data are not robust enough to converge on a single fault model, we built three different models encompassing all major geological evidence and the associated uncertainties, including the tectonic style and the location of major décollement levels. In all models the structures derived from the contractional phase play a significant role: from controlling segmentation to partially reusing inherited faults, to fully reactivating in extension a regional thrust, geometrically compatible with the source of the Norcia earthquake. Based on our conclusions, some additional seismogenic sources falling in the eastern, external portions of the Apennines may coincide with inherited structures. This may be a common occurrence in this region of the chain, where the inception of extension is as recent as Middle‐Upper Pleistocene.

In recent years, new approaches for developing earthquake rupture forecasts (ERFs) have been proposed to be used as an input for probabilistic seismic hazard assessment (PSHA). Zone- based approaches with seismicity rates derived from earthquake catalogs are commonly used in many countries as the standard for national seismic hazard models. In Italy, a single zone- based ERF is currently the basis for the official seismic hazard model. In this contribution, we present eleven new ERFs, including five zone-based, two smoothed seismicity-based, two fault- based, and two geodetic-based, used for a new PSH model in Italy. The ERFs were tested against observed seismicity and were subject to an elicitation procedure by a panel of PSHA experts to verify the scientific robustness and consistency of the forecasts with respect to the observations. Tests and elicitation were finalized to weight the ERFs. The results show a good response to the new inputs to observed seismicity in the last few centuries. The entire approach was a first attempt to build a community-based set of ERFs for an Italian PSHA model. The project involved a large number of seismic hazard practitioners, with their knowledge and experience, and the development of different models to capture and explore a large range of epistemic uncertainties in building ERFs, and represents an important step forward for the new national seismic hazard model.

The 2016–2017 Central Italy earthquakes have shown that the local seismic risk is dominated by the extreme vulnerability of the building stock. We attempt to rank the vulnerability of Apennines' settlements based on a combined geological-historical approach. We first discuss the reasons of the apparent paradox caused by the very different seismic response of Amatrice and Norcia, both strongly hit by the 24 August 2016 earthquake (Mw 6.0). Based on the awareness that strong earthquakes force building reconstructions and changes in the individual and societal perception of seismic risk, we assume that the global vulnerability of Italian settlements increases with time since the last significant earthquake. We focus on the very active seismogenic areas straddling Italy's Apennines. We then use data on the local seismogenic sources and earthquake history to (1) select the municipalities that are more likely to suffer from destructive ground shaking, and (2) rank them as a function of the time elapsed since the latest earthquake, i.e. in terms of increasing vulnerability. We hence identified 716 municipalities, totaling about 5% of the Italian population, over 50% of which have not experienced destructive shaking since 1861, when the Kingdom of Italy reunited a number of smaller states. As such they are primary candidates to a poor performance in future significant earthquakes (Mw > 5.5) and should be given priority in any statewide vulnerability reduction plan. All results and elaborations, including the seismic histories of each of the selected localities, are also supplied in a specifically designed web-GIS.

For any scientist working in seismotectonics, the Calabrian Arc represents the most challenging area of Italy. Lying on top of a subduction zone, it is characterised by a complex geological structure largely inherited from the early stages of the collision between the Africa and Eurasia plates. The current and extremely vigorous seismogenic processes, although generated by a mechanism driven by the subduction, are no longer a direct consequence of plate convergence. About one fourth of the largest Italian earthquakes concentrates in a narrow strip of land (roughly 200×70 km) corresponding to the administrative region of Calabria. The present-day seismicity, both shallow and deep, provides little help in detecting the most insidious seismogenic structures, nor does the available record of GPS-detected strains. In addition to its fierce seismicity, the Calabrian Arc also experiences uplift at rates that are the largest in Italy, thus suggesting that active tectonic processes are faster here than elsewhere in the country. Calabrian earthquakes are strong yet inherently elusive, and even the largest of those that have occurred over the past two centuries do not appear to have caused unambiguous surface faulting. The identified active structures are not sufficient to explain in full the historical seismicity record, suggesting that some of the main seismogenic sources still lie unidentified, for instance in the offshore. As a result, the seismogenic processes of Calabria have been the object of a lively debate at least over the past three decades. In this work we propose to use the current geodynamic framework of the Calabrian Arc as a guidance to resolve the ambiguities that concern the identification of the presumed known seismogenic sources, and to identify those as yet totally unknown. Our proposed scheme is consistent with the location of the largest earthquakes, the recent evolution of the regions affected by seismogenic faulting, and the predictions of current evolutionary models of the crust overlying a W-dipping subduction zone.

Determining the hypocentral depth of pre-instrumental earthquakes is a long-standing geophysical issue that still awaits to be elucidated. Using very well documented recent earthquakes we found that the depth of crustal and upper-mantle events correlates well with the slope of the first 50 km of their intensity attenuation curve, regardless of their magnitude. We used this observation to build a magnitude-independent method for calculating the depth of selected historical and early-instrumental earthquakes of northern Italy based on their macroseismic intensity field. Our method relies on both standard intensity data and questionnaire-based data for 20 earthquakes, encompassing a relatively large range of magnitude (Mw 4.0–5.8) and depth (3.0–72.4 km), that occurred in Northern Italy between 1983 and 2019. We then used the method to estimate the depth of 20 older earthquakes that occurred in the same region between 1570 and 1972. Knowing the approximate depth of historical earthquakes is crucial for assigning them to the relevant seismogenic source, especially where seismogenic faults occur at different depths, allowing for a better characterisation of the region’s seismotectonic setting. Knowing the focal depth also allows recalculating the equivalent magnitude, which turns out to be consistently larger for deeper events, suggesting a reassessment of the local seismic hazard.

A key element for assessing seismic hazard and risk is the availability of a comprehensive dataset on past earthquakes. Here we present the rationale, structure and contents of CFTI5Med (10.6092/ingv.it-cfti5), the 2018 version of the Catalogue of Strong Earthquakes in Italy: a large multidisciplinary effort including historians, seismologists and geologists. It was conceived in 1989, following the inception of GIS technology, and first published in 1995 to offer a full account of Italy’s strongest earthquakes, of their territorial impact and associated social and economic upheaval. Subsequent versions (1997, 2000, 2007) entailed a fine tuning of research methodologies, included additional research on Italian earthquakes, and were extended to large earthquakes of the Mediterranean area. CFTI5Med comprised an opportunity to streamline the structure of the Catalogue database and propose a renovated user interface. The new front-end (1) grants an easier, intuitive access to the data, including earthquake effects on the environment, and (2) allows all data to be displayed jointly with relevant topographic, geological and seismological overlays published as web services., Design Type(s)data integration objective • source-based data analysis objectiveMeasurement Type(s)earthquakeTechnology Type(s)digital curationFactor Type(s)geographic location • temporal_intervalSample Characteristic(s)Mediterranean Region Machine-accessible metadata file describing the reported data (ISA-Tab format)

The article by Camassi and Castelli (2013) (hereinafter CC13) deals with the 1346, northern Italy earthquake, one of hundreds of medieval earthquakes that were investigated in Italy from 1983 to 2007. Regrettably, the article does not add any new data but only proposes a revision and a reinterpretation of published materials. CC13 first criticized the variability of magnitude estimates assigned to this earthquake in catalogs published in Italy over the past 20 years, then went so far as to question whether the 1346 earthquake actually occurred. Their analysis, however, is fraught with demonstrable mistakes in the analysis of medieval texts, such that their conclusions are objectionable both from the point of view of historical criticism and from that of historical seismology. Such conclusions may critically affect the assessment of seismic hazard in a heavily populated and industrialized portion of the Po Plain (northern Italy), right at a time when the threat posed by strong earthquakes in this region is being rediscovered by the citizens and by their administrators following the 20 and 29 May 2012, Emilia events ( M w 6.0 and 5.9). As the coauthors of the catalogs being questioned, we feel an obligation to re‐establish what is the evidence supporting 1346 being a real major earthquake and why its magnitude is still uncertain. CC13 stated that three successive versions (Boschi et al. , 1997, 2000; Guidoboni et al. , 2007) of the Catalogo dei Forti Terremoti in Italia (CFTI), referred to as an authoritative study, “…did noticeably alter the epicentral location and estimated energy of the 1346 earthquake, but without explaining why these alterations had become necessary…”. First, we must recall that all of these studies, as well as the first version of CFTI (Boschi et al. , 1995), are not specific studies of the 1346 earthquake, as it might …

Most damaging earthquakes come as complex sequences characterized by strong aftershocks, sometimes by foreshocks and often by multiple mainshocks. Complex earthquake sequences have enormous seismic hazard, engineering and societal implications as their impact on buildings and infrastructures may be much more severe at the end of the sequence than just after the mainshock. In this paper we examine whether historical sources can help characterizing the rare earthquake sequences of preinstrumental times in full, including fore-, mainand aftershocks. Thanks to the its huge documentary heritage Italy relies on one of the richest parametric earthquake catalogues worldwide. Unfortunately most current methods for assessing seismic hazard require that earthquake catalogues be declustered by removing all shocks that bear some dependency with those identified as mainshocks. We maintain that this requirement has forced historical seismologists to focus only on mainshocks rather than also on the foreand aftershocks. To shed light onto major earthquake sequences of the past, rather than onto individual mainshocks, we investigated 10 damaging earthquake sequences (Mw 4.7-7.0) that hit the L’Aquila area and central Abruzzo from the XIV to the XX century. We find that most of the results of historical research are crucial for modern seismology, yet their rendering by the current parametric catalogues causes most information to be lost, or not easily trasnferred to the potential users. For this reason we advocate a change in current strategies and the creation of a more flexible standard for storing and using all the information made available by historical seismology.

Large earthquakes occur rather orderly in space and time; hence they can be somehow anticipated, and their effects can be projected into the future. The modern practice of seismic hazard assessment rests on these principles and may rely on them, but also requires a detailed knowledge of the location and characteristics of individual earthquake sources. We discuss how this knowledge base can be constructed, with an eye on the geological history, which provides a record of the faults capable of generating large earthquakes, and one on the human history, which supplies evidence for whether, where and how these faults have actually caused damaging earthquakes in the past. How do these two records interact with each other? It is now accepted that identifying active and potentially seismogenic faults in Italy is especially hard. The geological record may be clear and honest when dealing with processes at the scale of several million years, but can be very difficult to decipher if we are concerned with contemporary geological processes, such as earthquakes. Shortening the tim E-W indow of observation of earthquake activity is why Historical Seismology is so crucial for constructing a seismogenic source model. To this end we exploited a number of key Italian destructive earthquakes, each of which illuminates a recent geological process that may not offer a discernible surface signature. Our findings led us to reconsider the tectonic style of large areas, changed our perception of their earthquake potential, hinted at the existence of unknown seismogenic zones, and even led to downsizing the magnitude of the largest Italian historical earthquakes. We maintain that the complexity of the geological setting may be counterbalanced by the richness of the historical earthquake record. We also believe that our experience in the combined investigation of Italy’s historical earthquakes and seismogenic sources may be replicated in all earthquake-prone countries that exhibit a history of human settlement throughout the millennia.

We present a systematic and updated overview of a seismotectonic model for the Po Plain (northern Italy). This flat and apparently quiet tectonic domain is, in fact, rather active as it comprises the shortened foreland and foredeep of both the Southern Alps and the Northern Apennines. Assessing its seismic hazard is crucial due to the concentration of population, industrial activities, and critical infrastructures, but it is also complicated because (a) the region is geologically very diverse, and (b) nearly all potential seismogenic faults are buried beneath a thick blanket of Pliocene–Pleistocene sediments, and thus can be investigated only indirectly. Identifying and parameterizing the potential seismogenic faults of the Po Plain requires proper consideration of their depth, geometry, kinematics, earthquake potential and location with respect to the two confronting orogens. To this end, we subdivided them into four main, homogeneous groups. Over the past 15 years we developed new strategies for coping with this diversity, resorting to different data and modeling approaches as required by each individual fault group. The most significant faults occur beneath the thrust fronts of the Ferrara-Romagna and Emilia arcs, which correspond to the most advanced and buried portions of the Northern Apennines and were the locus of the destructive May 2012 earthquake sequence. The largest known Po Plain earthquake, however, occurred on an elusive reactivated fault cutting the Alpine foreland south of Verona. Significant earthquakes are expected to be generated also by a set of transverse structures segmenting the thrust system, and by the deeper ramps of the Apennines thrusts. The new dataset is intended to be included in the next version of the Database of Individual Seismogenic Sources (DISS; http://diss.rm.ingv.it/diss/ , version 3.2.0, developed and maintained by INGV) to improve completeness of potential sources for seismic hazard assessment.

Over the past few years the assessment of the earthquake potential of large continental faults has increasingly relied on field investigations. State-of-the-art seismic hazard models are progressively complementing the information derived from earthquake catalogs with geological observations of active faulting. Using these observations, however, requires full understanding of the relationships between seismogenic slip at depth and surface deformation, such that the evidence indicating the presence of a large, potentially seismogenic fault can be singled out effectively and unambiguously. We used observations and models of the 6 April 2009, Mw 6.3, L'Aquila, normal faulting earthquake to explore the relationships between the activity of a large fault at seismogenic depth and its surface evidence. This very well-documented earthquake is representative of mid-size yet damaging earthquakes that are frequent around the Mediterranean basin, and was chosen as a paradigm of the nature of the associated geological evidence, along with observational difficulties and ambiguities. Thanks to the available high-resolution geologic, geodetic and seismological data aided by analog modeling, we reconstructed the full geometry of the seismogenic source in relation to surface and sub-surface faults. We maintain that the earthquake was caused by seismogenic slip in the range 3–10 km depth, and that the slip distribution was strongly controlled by inherited discontinuities. We also contend that faulting was expressed at the surface by pseudo-primary breaks resulting from coseismic crustal bending and by sympathetic slip on secondary faults. Based on our results we propose a scheme of normal fault hierarchization through which all surface occurrences related to faulting at various depths can be interpreted in the framework of a single, mechanically coherent model. We stress that appreciating such complexity is crucial to avoiding severe over- or under-estimation of the local seismogenic potential.

We show and discuss the similarities among the 2016 Amatrice (Mw 6.0), 1997 Colfiorito-Sellano (Mw 6.0-5.6) and 2009 L’Aquila (Mw 6.3) earthquakes. They all occurred along the crest of the central Apennines and were caused by shallow dipping faults between 3 and 10 km depth, as shown by their characteristic InSAR signature. We contend that these earthquakes delineate a seismogenic style that is characteristic of this portion of the central Apennines, where the upward propagation of seismogenic faults is hindered by the presence of pre-existing regional thrusts. This leads to an effective decoupling between the deeper seismogenic portion of the upper crust and its uppermost 3 km.The decoupling implies that active faults mapped at the surface do not connect with the seismogenic sources, and that their evolution may be controlled by passive readjustments to coseismic strains or even by purely gravitational motions. Seismic hazard analyses and estimates based on such faults should hence be considered with great caution as they may be all but representative of the true seismogenic potential.

This work aims at providing an updated and augmented view of present-day tectonics and seismogenic sources of the Abruzzi Apennines, focusing on its extensional domain. This paper was spurred by the 6 April 2009, L’Aquila earthquake (M w 6.3), an event from which geologists learned important lessons-including rather surprising ones. Although the earthquake was not major compared with other catastrophic events that occurred in Italy and elsewhere, this destructive earthquake led to a thorough review of the geometry – and style, in some instances – that characterises earthquake faulting in this region. The poorly expressed field evidence of the 6 April event, especially in light of the damage it caused in the mesoseismal area, stressed the intrinsic limitation of the earthquake geologists’ toolbox. Abruzzi is the region of a true “seismological paradox”: despite the rather long earthquake history available for the region, the number of potential sources for earthquakes of M ≥ 6.0 proposed in the literature is two to five times larger than the number of events that appear in the full earthquake record. This circumstance is made even more paradoxical by recent palaeoseismological work that proposed recurrence times of only a few centuries for individual seismogenic sources. Do the evident faults mapped by previous workers all correspond to potential seismogenic sources? We aim at addressing this paradox by drawing an updated seismotectonic model of Abruzzi based on the lessons learned following the 2009 earthquake. The model is based on selected geological, geomorphological, seismological, historical and geodetic data and will ultimately feed an updated version of the DISS database (http://diss.rm.ingv.it/diss/).

The 31 October and 1 November 2002 Molise earthquakes (both M w 5.7) were caused by right-lateral slip between 12 and 20 km depth. These earthquakes are the result of large-scale reactivation of preexisting, left-lateral, regionally extended east–west structures of Mesozoic age. Although recorded ground motions were generally smaller than expected for typical Italian earthquakes, a recent paper attributes a stress drop as high as 180 bars to the Molise earthquakes. We remark that a high stress drop is in contrast both with the relatively long source duration inferred in previous investigations and with geodetic evidence for a significantly smaller fault slip compared with other Apennine earthquakes having similarly large rupture area (e.g., 1997 Umbria–Marche earthquakes). We analyzed both ground acceleration spectra of the mainshocks and single-station spectral ratios of broadband seismograms in an extended magnitude range (2.7≤ M w≤5.7). Our results show that neither the spectral amplitudes of recorded ground motions nor the spectral ratios can be fit by a high stress-drop source. Instead we find that the observations are consistent with a low stress drop, our best estimates ranging between 6 and 25 bars, in agreement with the relatively long source duration and small coseismic slip. We interpret the low stress of the 2002 Molise earthquakes in terms of lower energy release mechanisms due to the reutilization of faults reactivated opposite to their original sense of slip.

The outermost, NE-verging fronts of the Northern Apennines (Italy) are overlain by a thick syntectonic sedimentary wedge filling up the basin beneath the Po Plain. Due to fast sedimentation rates and comparatively low tectonic rates, the fronts are generally buried. Evidence for their activity includes scattered historical and instrumental earthquakes and drainage anomalies controlled by growing buried anticlines. The largest earthquakes, up to M w 5.8, are associated with active compression, with a GPS-documented shortening rate

Early in the morning on 28 December 1908, just a few days after Christmas, a severe earthquake struck the Messina Straits, a rather narrow sound that separates Calabria, in southern Italy, from Sicily (Figure 1). The shaking was distinctly felt in Albania, Montenegro, and the Greek Ionian islands, about 400 km to the east and northeast of the Straits; in Malta, about 250 km to the south; and as far as Ustica Island, about 220 km to the west. The earthquake was catastrophic in the epicentral area and was immediately followed by fires and a large tsunami. Messina (Sicily) and Reggio Calabria (Calabria), two significant cities located less than 10 km apart on the two facing shores of the straits, were almost completely destroyed, and buildings were severely damaged over an area in excess of 6,000 km2. Of the population at the time, estimated to number 140,000 at Messina and 45,000 at Reggio Calabria, a significant fraction was reported dead. Assessing the total number of victims has been problematic, as fatality estimates range from 60,000 to more than 100,000, yet 1908 was undeniably the deadliest European earthquake ever and one of the deadliest worldwide. Guidoboni et al. (2007) contend that 80,000 people were killed by the earthquake, including as many as 2,000 who died as a result of the tsunami. Waves up to 12 m struck the shorelines south of Messina and south of Reggio Calabria, displacing the rubble from collapsed buildings and completing the destruction. All communications in the affected area were disrupted, and rescue operations had to rely on access from the sea. Units of the Russian and English navies, already in the area, were the first to offer immediate relief. In particular, medical officers of the Baltic Guard-Marine brought the first medical aid to the …

We calculated the expected impact on the Italian coast of the Adriatic Sea of a large set of tsunamis resulting from potential earthquakes generated by major fault zones. Our approach merges updated knowledge on the regional tectonics and scenario-like calculations of expected tsunami impact. We selected six elongated potential source zones. For each of them we determined a Maximum Credible Earthquake and the associated Typical Fault, described by its size, geometry and kinematics. We then let the Typical Fault float along strike of its parent source zone and simulated all tsunamis it could generate. Simulations are based on the solution of the nonlinear shallow water equations through a finite-difference technique. For each run we calculated the wavefields at specified simulation times and the maximum water height field (above mean sea level), then generated travel-time maps and maximum water height profiles along the target coastline. Maxima were also classified in a three-level code of expected tsunami threat. We found that the southern portion of Apulia facing Albania and the Gargano promontory are especially prone to the tsunami threat. We also found that some bathymetric features are crucial in determining the focalization-defocalization of tsunami energy. We suggest that our results be taken into account in the design of early-warning strategies.

Recent seismicity in and around the Gargano Promontory, an uplifted portion of the Southern Adriatic Foreland domain, indicates active E–W strike-slip faulting in a region that has also been struck by large historical earthquakes, particularly along the Mattinata Fault. Seismic profiles published in the past two decades show that the pattern of tectonic deformation along the E–W-trending segment of the Gondola Fault Zone, the offshore counterpart of the Mattinata Fault, is strikingly similar to that observed onshore during the Eocene–Pliocene interval. Based on the lack of instrumental seismicity in the south Adriatic offshore, however, and on standard seismic reflection data showing an undisturbed Quaternary succession above the Gondola Fault Zone, this fault zone has been interpreted as essentially inactive since the Pliocene. Nevertheless, many investigators emphasised the genetic relationships and physical continuity between the Mattinata Fault, a positively active tectonic feature, and the Gondola Fault Zone. The seismotectonic potential of the system formed by these two faults has never been investigated in detail. Recent investigations of Quaternary sedimentary successions on the Adriatic shelf, by means of very high-resolution seismic–stratigraphic data, have led to the identification of fold growth and fault propagation in Middle–Upper Pleistocene and Holocene units. The inferred pattern of gentle folding and shallow faulting indicates that sediments deposited during the past ca. 450 ka were recurrently deformed along the E–W branch of the Gondola Fault Zone. We performed a detailed reconstruction and kinematic interpretation of the most recent deformation observed along the Gondola Fault Zone and interpret it in the broader context of the seismotectonic setting of the Southern Apennines-foreland region. We hypothesise that the entire 180 km-long Molise–Gondola Shear Zone is presently active and speculate that also its offshore portion, the Gondola Fault Zone, has a seismogenic behaviour.

On 16 December 1857, a strong earthquake ( M ∼7) struck a large portion of the southern Apennines about 150 km southeast of Naples. The earthquake was thoroughly investigated by Irish engineer Robert Mallet, who wrote an extensive report that is still regarded as a landmark in observational seismology. Because of the concentration of damage in the High Agri valley, and contrary to Mallet’s own findings, for many years the earthquake was referred to as the “Val d’Agri earthquake” and was believed by most investigators to have ruptured the 20–25-km normal fault lying beneath this intermontane basin. The magnitude of the earthquake, however, and evidence for earthquake complexity suggest that the true rupture length has been so far underestimated. We contend that the 1857 earthquake ruptured in a cascade fashion two adjacent and relatively well-known faults: first the smaller Melandro–Pergola fault, commonly believed to represent a seismic gap between the causative faults of the 1857 and of the 1980 Irpinia ( M w 6.9) earthquakes; and then the larger Agri valley fault proper. Contemporary chronicles reported a time lapse of 2–3 min between the two ruptures, thus effectively making them two independent shocks. The rupture must have proceeded unilaterally from the northwestern edge of the Melandro–Pergola fault, where Mallet placed the earthquake epicenter, thus explaining the concentration of damage—and attention by rescue crews and subsequent investigators—in the southeastern portion of the High Agri valley.

We reconstruct the tectonic framework of the 24 August 2016, Amatrice earthquake. At least three main faults, including an older thrust fault (Sibillini Thrust), played an active role in the sequence. The mainshock nucleated and propagated along an extensional fault located in the footwall of the Sibillini Thrust, but due to the preliminary nature of the data the role of this thrust is still unclear. We illustrate two competing solutions: 1) the coseismic rupture started along an extensional fault and then partially used the thrust plane in extensional motion; 2) the thrust fault acted as an upper barrier to the propagation of the mainshock rupture, but was partially reactivated during the aftershock sequence. In both cases our tectonic reconstruction suggests an active role of the thrust fault, providing yet another example of how structures inherited from older tectonic phases may control the mainshock ruptures and the long-term evolution of younger seismogenic faults.

The active tectonics at the front of the Southern Apennines and in the Adriatic foreland is characterized by E–W striking, right-lateral seismogenic faults, interpreted as reactivated inherited discontinuities. The best studied among these is the Molise-Gondola shear zone (MGsz). The interaction of these shear zones with the Apennines chain is not yet clear. To address this open question, we developed a set of scaled analogue experiments, aimed at analyzing: (1) how dextral strike–slip motion along a pre-existing zone of weakness within the foreland propagates toward the surface and affects the orogenic wedge; (2) the propagation of deformation as a function of increasing displacement; (3) any insights on the active tectonics of Southern Italy. Our results stress the primary role played by these inherited structures when reactivated, and confirm that regional E–W dextral shear zones are a plausible way of explaining the seismotectonic setting of the external areas of the Southern Apennines.

We revisited data related to the 1456 seismic crisis, the largest earthquake to have ever occurred in peninsular Italy, in search of its causative source(s). Data about this earthquake consist solely of historical reports and their intensity assessment. Because of the age of this multiple earthquake, the scarcity and sparseness of the data, and the unusually large damage area, no previous studies have attempted to attribute the 1456 events to specific faults. Existing analytical methods to identify a likely source from intensity data also proved inappropriate for such a sparse dataset, since historical evidence suggests that the cumulative damage pattern contains at least three widely separated events. We subdivided the 1456 damage pattern into three independent mesoseismal areas; each of these areas falls onto east–west tectonic trends previously identified and marked by deep (>10 km) right-lateral slip earthquakes. Based on this evidence we propose (1) that the 1456 events were generated by individual segments of regional east–west structures and are evidence of a seismogenic style that involves oblique dextral reactivation of east–west lower crustal faults; (2) that each event may have triggered subsequent but relatively distant events in a cascade fashion, as suggested by historical accounts; hence (3) that the 1456 sequence reveals a fundamental but unexplored mechanism of tectonic deformation and seismic release in southern Italy. This style dominates the region that lies between the northwest–southeast system of large extensional faults straddling the crest of the southern Apennines and the buried outer front of the chain. Although the quality of the available information concerning the 1456 earthquake is naturally limited, we show that the overlap of the damage distribution, the orientation and characteristics of regional tectonic structures, the seismicity patterns, and the focal mechanisms all concur with our interpretations and would be difficult to justify otherwise.

Five large earthquakes shook southern Calabria in February–March 1783. We focused on the first shock (Me 6.9), which occurred on 5 February in the Gioia Tauro Plain. Most investigators attribute the event to a W-dipping, high-angle fault running at the base of the Aspromonte crystalline bedrock on the ESE side of the Plain (Aspromonte Fault). Other workers contend that the earthquake was generated by an E-dipping, low-angle blind fault (Gioia Tauro Fault) similar to the adjacent Messina Straits Fault. In 1999–2000 we carried out four geochemical surveys in the Gioia Tauro Plain with the aim of contributing to this debate with an independent line of evidence. We sampled 240 groundwater sites and measured a suite of in-situ physical and chemical parameters. Our goal was to gain new insight into the seismogenic source by identifying geochemical anomalies associated with the deepening of the hydrological circuits due to the presence of enhanced faulting/fracturing. The deep-fluid signatures are mainly represented by temperature, salinity, total carbon and radon anomalies. We identified three zones of dominant deep fluid discharge: the Nicotera-Galatro area (along the Nicotera-Galatro portion of the NW-trending Nicotera-Gioiosa Jonica lineament), a small NW-SE trending area between Gioia Tauro and Seminara, and the coastline between Rosarno and Palmi. This latter sector locates just above the upper edge of the hypothesised Gioia Tauro Fault. Most of the geochemical anomalies are recorded around Rosarno, at the intersection between the Gioia Tauro Fault and the Nicotera-Gioiosa Jonica lineament. In contrast, no evidence of groundwater deepening and active fracturing was found along the Aspromonte Fault. Based on our new findings we updated the concepts of Geochemically Active Fault Zone and Geochemical Interaction Fault Zone in view of the modern understanding of the hydro-mechanical properties of fault zones and the faulting mechanisms promoting fracture permeability in the crust.

The Northern Marche coastal belt is characterised by a series of NW-SE trending, NE verging folds forming the easternmost edge of the Apennines thrust front. Several geomorphic features suggest that the folds are still growing and hence that the thrust front is active. The occurrence of several historical and instrumental earthquakes (e.g. 1672, 1690, 1786, 1875, 1916, 1930, 1972, all having Me≥ 5.2) suggests that the thrust faults are also seismogenic.

Two Mw 5.7 earthquakes struck a sparsely populated region of southern Italy, on October 31 and November 1, triggering a swarm-like sequence that lasted for several days. The earthquakes were caused by pure right-lateral slip between 10 and 24 km depth over a nearly vertical, previously undetected east-west fault. This mechanism is not typical for southern Italy, where normal faulting in the uppermost 12 km of the crust seems to dominate. However, east-west strike-slip faulting is kinematically consistent with the widely documented Apennines extension. The earthquake-causative fault appears to connect the Mattinata fault, a major active strike-slip feature cutting across the Gargano promontory, with east-west structures known beneath the axial part of the Apennines. The 2002 earthquakes thus highlighted a mode of earthquake release that may explain several large yet poorly understood historical earthquakes (e.g., 1361, 1456, 1731, 1930) located between the crest of the Apennines and the Adriatic coastline.

SUMMARY We analysed elevation changes induced by the 1997‐1998 Umbria-Marche, central Apennines (Italy) earthquakes. We employed data from a first-order geodetic levelling line measured in 1951, 1992 and 1998. The line bears a record of pre-seismic and coseismic strains associated with the causative fault of the 1997 September 26, 09:40 mainshock (Mw = 6.0). A first level analysis performed under the assumption of slip homogeneity of coseismic slip shows misfits that cannot be reduced simply by altering the fault size and geometry. A more detailed analysis based on a distribution of coseismic slip obtained from broad-band seismograms provides a better fit and is in agreement with 1951‐1992 elevation changes interpreted as precursory slip by previous investigators. The levelling data sets new constraints on the location, extent, dip and depth of the fault, in full agreement with seismological evidence and images from SAR interferometry. The data show no evidence for slip in the uppermost 3 km of the crust, suggesting that a major and widely recognized normal fault that exists in the area is no longer active and showing a tendency of present tectonic strains to revert the current topographic setting.

Terra Nova, 23, 421–423, 2011 Abstract We reply to a comment by Messina et al., who strongly criticized our article on the San Pio Fault, by showing that in areas of complex geology such as the central Apennines, where the current tectonic setting results from the superposition of different tectonic regimes, the equation: `most visible active fault = major seismogenic fault' can be misleading.

While scientists are paying increasing attention to the seismicity potentially induced by hydrocarbon exploitation, so far, little is known about the reverse problem, i.e. the impact of active faulting and earthquakes on hydrocarbon reservoirs. The 20 and 29 May 2012 earthquakes in Emilia, northern Italy (Mw 6.1 and 6.0), raised concerns among the public for being possibly human-induced, but also shed light on the possible use of gas wells as a marker of the seismogenic potential of an active fold and thrust belt. We compared the location, depth and production history of 455 gas wells drilled along the Ferrara-Romagna arc, a large hydrocarbon reserve in the southeastern Po Plain (northern Italy), with the location of the inferred surface projection of the causative faults of the 2012 Emilia earthquakes and of two pre-instrumental damaging earthquakes. We found that these earthquake sources fall within a cluster of sterile wells, surrounded by productive wells at a few kilometres' distance. Since the geology of the productive and sterile areas is quite similar, we suggest that past earthquakes caused the loss of all natural gas from the potential reservoirs lying above their causative faults. To validate our hypothesis we performed two different statistical tests (binomial and Monte Carlo) on the relative distribution of productive and sterile wells, with respect to seismogenic faults. Our findings have important practical implications: (1) they may allow major seismogenic sources to be singled out within large active thrust systems; (2) they suggest that reservoirs hosted in smaller anticlines are more likely to be intact; and (3) they also suggest that in order to minimize the hazard of triggering significant earthquakes, all new gas storage facilities should use exploited reservoirs rather than sterile hydrocarbon traps or aquifers.

We summarise and discuss almost a century of progress inthe understanding of the main characteristics of large Italian earthquakes.Topics of discussion include (1) the distribution of the largest earthquakesin relation with Late Pleistocene and Holocene faulting, (2) the geologicaland tectonic setting of the 1908 Messina Straits, 1915 Fucino Plain and1980 Irpinia earthquakes, (3) some of the geodynamic motivations for thecharacteristics of Italian seismicity, and (4) the resulting implications for theassessment of seismic hazard. In a subsequent section of the paper we present a summaryof recent achievements in the understanding and characterization of Italianseismicity, with special emphasis on the assignment of large historicalearthquakes to specific sources identified through geological observationsand on the evaluation of average recurrence intervals for individualearthquake sources. The final section describes some of the efforts being madefor matching the newly acquired geological evidence with instrumental andhistorical observations of Italian seismicity and the hypotheses than can bederived for anticipating the locus of large earthquakes of the future.

We find that the genesis of San Clemente Island and its surrounding submarine platform is consistent with progressive slip on two, southeast-striking, southwest-dipping, blind thrust fault segments. Since their inception 2 to 5 Ma, 3 km of compression normal to the N150°E fault strike has been accommodated with 1700 m of domal uplift of the San Clemente Anticlinorium. The existence of an extensive suite of Pleistocene marine terraces provides evidence that slip and uplift are continuing today. Based on direct terrace fossil age determinations and correlations of terrace heights with global sea-level curves, we estimate that San Clemente Island is currently uplifting at between 0.2 and 0.5 mm yr−1. This translates into 0.6–1.5 mm yr−1 of thrusting on the causative blind thrusts beneath the island. Unlike the situation at nearby Palos Verdes, where a simple twist in a regional strike-slip fault accommodated both fault-parallel and fault-normal motions, the shallow dips of the thrusts suggest that, if regional strike-slip motion on the San Clemente Fault exists, it must be partitioned onto through-going surfaces distinct from the thrusts. Current GPS data are sparse and equivocal, but they indicate that 1–4 mm yr−1 of compression and 4–7 mm yr−1 of strike slip are absorbed in the California Continental Borderland. With the Palos Verdes Fault taking some 3 mm yr−1 from the strike-slip budget, 1–4 mm yr−1 of motion could be present on a through-going San Clemente Fault. When translated into an annual moment release rate using Kostrov's formula, GPS strains predict that between 2.5 and 4.9 times 1017 N m yr−1 of earthquake potential is available offshore from San Diego to the Santa Barbara Channel. Distribution of this moment budget among various earthquake magnitudes is arguable, but we predict that M > 6 quakes in the Borderland could recur between 30 and 80 years, and M > 7 quakes might be found every 310 to 580 years.

Understanding the relationship between seismogenic slip at depth and surface deformation is fundamental in any seismic hazard analysis because the assessment of the earthquake potential of large continental faults relies largely on field investigations. The well-documented 6 April 2009, Mw 6.3, L'Aquila earthquake affords a unique opportunity to explore the relationships between the activity of the deep source and its surface evidence. We used available high-resolution geologic, geodetic and seismological data aided by analogue modeling to reconstruct the geometry of the seismogenic rupture in relation with surface and sub-surface faults. We contend that the earthquake was caused by a blind fault, controlled at depth by pre-existing discontinuities and expressed at the surface by pseudo-primary breaks resulting from coseismic crustal bending. Finally, we propose a scheme for hierarchizing normal faults that explains all surface occurrences related to blind faulting in the frame of a single, mechanically coherent, interpretative model. Failure to appreciate such complexity may result in severe over– or under-estimation of the local seismogenic potential.

On May 20 and 29, 2012, two earthquakes of magnitudes 5.9 and 5.8 (Mw), respectively, and their aftershock sequences hit the central Po Plain (Italy), about 40 km north of Bologna. More than 2,000 sizable aftershocks were recorded by the Isti-tuto Nazionale di Geofisica e Vulcanologia (INGV; National Institute of Geophysics and Volcanology) National Seismic Network (http://iside.rm.ingv.it/). The sequence was generated by pure compressional faulting over blind thrusts of the western Ferrara Arc, and it involved a 50-km-long stretch of this buried outer front of the northern Apennines. The focal mechanisms of the larger shocks agree with available structural data and with present-day tectonic stress indicators, which show locally a maximum horizontal stress oriented ca. N-S; i.e. oriented perpendicular to the main structural trends. Most of the sequence occurred between 1 km and 12 km in depth, above the local basal detachment of the outer thrust fronts of the northern Apennines. We measured the surface displacement patterns associated with the mainshocks and some of the larger aftershocks (some of which had Mw >5.0) by applying the Interferometric Synthetic Aperture Radar (InSAR) technique to a pair of C-Band Radarsat-1 images. We then used the coseismic motions detected over the epicentral region as input information, to obtain the best-fit model fault for the two largest shocks. […]

For decades, alluvial plains have been the areas of the fastest population growth over most of the globe. Modern societies demand growing extensions of flat and easily accessible land to accommodate the swelling urban areas, booming industrial districts, large power plants, and multi-runway airports. But how can we tell if such flat areas hide large active faults? How can we assign a significant pre-instrumental earthquake to its causative source? In other words, how can modern societies deal with buried, that is to say, 'invisible' faults, and with the elusiveness of the hazards they can pose? The issue of blind faulting became widely debated in the Earth sciences community in 1989, following the publication of a summary on a sequence of 'hidden earthquakes' that hit central and southern California, USA, between 1983 and 1987, and following the October 17, 1989, Loma Prieta, California, earthquake (Mw 6.9). These earthquakes shattered the accepted belief that large earthquakes are associated with large topographic contrasts; i.e., that they usually take place in mountainous terrains, and that their causative faults are expressed at the surface. Stein and Yeats [1989] spelled out clearly that "...large earthquakes can take place not only on faults that cut the Earth's surface, but also on 'blind' faults under folded terrain". Due to the growing concentrations of population and infrastructures in low topography areas, although such earthquakes might pose comparable hazards, they can come with substantially greater risk than earthquakes that occur in hilly or mountainous terrains. [...]

Historical earthquakes of the Gargano Promontory, an uplifted foreland sector in southeastern Italy, have been usually regarded as generated by inland faults. Some have been associated with activity of the Mattinata fault, a section of a regional east-west shear zone. The 10 August 1893 Mw 5.4 event is one such earthquake, but its current onshore location is only loosely based on the damage pattern. Regions that were hit by offshore earthquakes are also known to be affected by a methodological bias such that offshore historical events appear to be located onshore. To test this condition for the 1893 earthquake, we pursued an alternative hypothesis for its location. The earthquake occurred near the Gondola fault zone, a right-lateral active fault system representing the offshore counterpart of the Mattinata fault and hence capable of producing sizable earthquakes along the Gargano coast. We focused on its westernmost segment, suggesting that it could be the causative fault of the 1893 earthquake (in agreement with both the damage distribution and reported environmental effects). The approach we present works side by side with the recent developments of the algorithms used to compile historical catalogs, providing a fine-scale, geologically based method to define or confirm the dubious location of historical earthquakes. Marine paleoseismology is a new field stemming from the increased capabilities of high-resolution marine techniques in supporting classical paleoseismological analyses for the exploration of the seismogenic potential of offshore faults. Based on Late Pleistocene and Holocene individual or cumulative earthquake records, the potential of offshore faults can now be constrained in terms of expected magnitude and recurrence intervals. We stress the importance of revisiting historical earthquakes in coastal zones using marine paleoseismological data to assess regional seismic hazard, particularly in tectonic settings where regional-size seismogenic areas straddle the onshore and the onshore-offshore zone.

Uplift of the Palos Verdes peninsula has long been associated with a northwest trending, southwest dipping, reverse fault. Unfortunately, the Palos Verdes Hills fault has no obvious surface displacement and little background seismicity to substantiate its dimension, orientation, or earthquake potential. In this paper we investigate the tectonic style and slip rate of the Palos Verdes Hills fault and the uplift history of the Palos Verdes Hills by analyzing the geometry of 13 marine terraces that encircle the peninsula in a bathtub ring configuration. Elevations of 211 terrace remnants constrain a fault model with 3.0 to 3.7 mm yr−1 of oblique, dextral/reverse slip on a fault dipping 67° at 6 to 12 km depth beneath the peninsula. If the rate was constant through time, fault inception would have occurred 2.4–3.0 Ma. We propose that the largest credible earthquakes on the fault have magnitude ≈6¾ and could revisit every 2000 years.

Terra Nova, 23, 108–115, 2011 Abstract We analysed a broad region around L'’Aquila in search of seismogenic faults similar to that responsible for the 6 April 2009 earthquake (Mw 6.3). Having in mind the lessons learned from this earthquake, we focused on adjacent areas displaying similar morphotectonic, geological and structural features. The basin running from Barisciano to Civitaretenga-Navelli, notably located near the southeastern edge of the 2009 aftershock pattern, appears to be one such area. We collected morphotectonic and structural data indicating that this basin is underlain by a major active normal fault (the San Pio Fault). All the observations are very much reminiscent of the morphotectonic, geological and structural setting of the area struck by the L'’Aquila earthquake, suggesting that the newly identified fault has the potential for a Mw 6.2 shock.

The catastrophic 28 December 1908, M w 7.1, Messina Straits earthquake was generated by a large, low-angle, SE-dipping, blind normal fault. A number of shallow, high-angle normal faults arranged in a graben-like fashion occur in the same area both on land and offshore, reaching the surface and in some instances affecting recent deposits. These faults are normally interpreted as active and have often been considered potentially seismogenic. We used an analogue modelling approach to simulate the evolution of a large, low-angle normal fault and investigate its relationships with the overlying secondary faults. We find that these faults represent the brittle surface expression of the long-term activity of the underlying master fault, and that all faults mapped by previous workers in the Messina Straits are compatible with sustained slip along the fault responsible for the 1908 earthquake. Our results confirm that analogue modelling provides a useful tool to investigate the evolution and the hierarchical relationships of fault systems, suggesting that this approach is effective in the investigation of complex seismogenic areas.

An edited version of this paper was published by AGU. Copyright (2010) American Geophysical Union

This is a rather unusual comment that focuses on how a specific figure was constructed rather than on actual scientific results. The figure in question (Figure 9 from Pino et al. 2009) does not even show new data or results, but is simply a summary of slip models that have been proposed in the literature for the 1908 earthquake. All models describe slip distributions from coseismic elevation changes except for one, derived by Pino et al. (2000) based on waveform modeling of historical seismograms. To construct Figure 9 we simply plotted the slip maxima obtained by different workers in a 2D diagram having the northward distance from a conventional point in the Ionian Sea on the x -axis and slip on the y -axis. The first two sentences of its caption read: “Slip distribution along-strike of the fault resulting from various studies. The diagram consistently shows the maximum slip recorded along each section of the fault.” The distribution reported as “Amoruso et al. (2002)” was based on their Model A (see our Figure 1 and Figure 1B of the comment). Model A exhibits two prominent maxima (respectively a and c in our Figure 1), described as follows in Amoruso et al. (2002): “the majority of the seismic moment is released in a region, ∼ 600 km2 in area, extending south of the Calabrian coastline (the highest slip is ∼ 6 m at a depth of ∼ 6 km); a smaller slip patch is 25 km NE of the Ganzirri peninsula, at a depth of ∼ 17 km.” Amoruso et al. (2010) claim that Figure 9 is “inconsistent and misleading”; they never explicitly say why, but propose an alternative, more subjective way of plotting the same data. We firmly believe our Figure 9 was constructed in a plain and easily …

The occurrence of characteristic earthquakes along segments of major active belts has been described as early as the beginning of the century. The large 1908, Messina Straits, blind normal faulting earthquake provides an opportunity to investigate the repetition of characteristic earthquakes and the persistency of the main features of the fault zone over a time-scale in the order of 100 Kyr. We have compared seismological and geodetic descriptions of the 1908 rupture process with long-term crustal deformation recorded at different stratigraphic levels by marine terraces, marine sedimentary units, and landscape features. The wealth of elevated coastal features in and around a region affected by large normal faulting earthquakes indicates that coseismic strain is superimposed on much faster uplift on a regional scale. We investigated in detail the pattern of deformation of the 125 Kyr-old, lowest emergent terrace, and found that it mimics the pattern of elevation changes observed following the earthquake. This suggests (1) that the 1908 earthquake is characteristic, (2) that its segment boundaries have been stationary during the past 125 Kyr, and (3) that even the locations of the regions of largest coseismic release do not change through many seismic cycles. Based on a comparison between observed heights of the 125 Kyr terrace and 1908 displacements, we estimated an average repeat time of 1000± yr for a 1908-type earthquake. We also investigated the height, position, age and state of deformation of older terraces, and found (1) that uplift of the region started about 1 Ma and has since continued rather uniformly at 0.9–1.4 mm yr-1, (2) that during this time the Straits have narrowed at a rate of 10–20 mm yr-1, and (3) that all the main geomorphic features of the Messina Straits result from the interaction of fast regional uplift, 1908-type coseismic subsidence, and global sea-level fluctuations.

We designed a new seismic source model for Italy to be used as an input for country-wide probabilistic seismic hazard assessment (PSHA) in the frame of the compilation of a new national reference map. We started off by reviewing existing models available for Italy and for other European countries, then discussed the main open issues in the current practice of seismogenic zoning. The new model, termed ZS9, is largely based on data collected in the past 10 years, including historical earthquakes and instrumental seismicity, active faults and their seismogenic potential, and seismotectonic evidence from recent earthquakes. This information allowed us to propose new interpretations for poorly understood areas where the new data are in conflict with assumptions made in designing the previous and widely used model ZS4. ZS9 is made out of 36 zones where earthquakes with M w > = 5 are expected. It also assumes that earthquakes with M w up to 5 may occur anywhere outside the seismogenic zones, although the associated probability is rather low. Special care was taken to ensure that each zone sampled a large enough number of earthquakes so that we could compute reliable earthquake production rates. Although it was drawn following criteria that are standard practice in PSHA, ZS9 is also innovative in that every zone is characterised also by its mean seismogenic depth (the depth of the crustal volume that will presumably release future earthquakes) and predominant focal mechanism (their most likely rupture mechanism). These properties were determined using instrumental data, and only in a limited number of cases we resorted to geologic constraints and expert judgment to cope with lack of data or conflicting indications. These attributes allow ZS9 to be used with more accurate regionalized depth-dependent attenuation relations, and are ultimately expected to increase significantly the reliability of seismic hazard estimates.

[1] The active tectonics at the front of the southern Apennines and in the Adriatic foreland is characterized by E-W striking, right-lateral seismogenic faults, interpreted as reactivated inherited discontinuities. The best studied among these is the Molise-Gondola shear zone. The interaction of these shear zones with the Apennines chain is not yet clear. To address this open question, we developed a set of scaled analogue experiments, aimed at analyzing (1) how dextral strike-slip motion along a preexisting zone of weakness within the foreland propagates toward the surface and affects the orogenic wedge; (2) the propagation of deformation as a function of displacement; and (3) any insights on the active tectonics of southern Italy. Our results stress the primary role played by these inherited structures when reactivated and confirm that regional E-W dextral shear zones are a plausible way of explaining the seismotectonic setting of the external areas of the southern Apennines.

[1] Destructive earthquakes are rare in France yet pose a sizable seismic hazard, especially when critical infrastructures are concerned. Only a few destructive events have occurred within the instrumental period, the most important being the 11 June 1909, Lambesc (Provence) earthquake. With a magnitude estimated at 6.2 [Rothe, 1942], the event was recorded by 30 observatories and produced intensity IX effects in the epicentral area, ∼30 km north of Marseille. We collected 30 seismograms, leveling data, and earthquake intensities to assess the magnitude and possibly the focal mechanism of this event. Following this multidisciplinary approach, we propose a source model where all relevant parameters are constrained by at least two of the input data sets. Our reappraisal of the seismological data yielded Mw 5.7–6.1 (6.0 preferred) and Ms 6.0, consistent with the magnitude from intensity data (Me 5.8) and with constraints derived from modeling of coseismic elevation changes. Hence we found the Lambesc earthquake to have been somewhat smaller than previously reported. Our data sets also constrain the geometry and kinematics of faulting, suggesting that the earthquake was generated by reverse-right lateral slip on a WNW-striking, steeply north-dipping fault beneath the western part of the Trevaresse fold. This result suggests that the fold, located in front of the Luberon thrust, plays a significant role in the region's recent tectonic evolution. The sense of slip obtained for the 1909 rupture also agrees with the regional stress field obtained from earthquake focal mechanisms and microtectonic data as well as recent GPS data.

The Po Plain is a low-relief area characterised by active shortening accommodated by blind thrust faulting. In this almost flat region depositional rates are similar to tectonic rates and deformation is seldom expressed by noticeable surface anticlines. We adopted a geomorphological approach based on the detailed analysis of the drainage network to identify the location of active thrust faults. A total of 36 anomalies represented by sudden river diversions and shifts in channel pattern were accurately mapped. After comparison with the location of subsurface buried anticlines and of historical seismicity, these anomalies could be related to a tectonic origin and included in a database. Their distribution highlights the activity of the buried outer thrust fronts of both the Southern Alps and the Northern Apennines. Among all the anomalies, we identified one related to the seismogenic source responsible for the 12 May 1802 earthquake (Me 5.7), which struck the Oglio River Valley near Soncino (Cremona). We propose that this earthquake was generated by an east-west trending, north-dipping, blind thrust fault that roots into the Alpine system. If this inference is correct, other faults along the Southern Alpine margin are potentially seismogenic.

The earthquake history of Italy is not just a history of ruined cities and people struggling to revive their environment; the distribution of the population, the abandonment and relocation of many settlements, the development and enforcement of modern town-planning rules, the creation of new architectural styles, and even the distribution of dialects can sometimes be blamed on the occurrence of a large earthquake. Although Italian earthquakes may not be the largest ever spawned by Earth, they contribute significantly to the development of seismology as a science. Important milestones, such as the following, in the earthquake history of the peninsula testify to this

The direct identification of seismogenic structures in Southern Italy is often a difficult task, since finding seismogenic faults with clear surface expression associated is unlikely, even if they are the source of large magnitude earthquakes. A possible way to solve this problem is the investigation of a series of features of the surface landscape that could be attributed to repeated movements along a fault. In this paper we investigated the drainage, ancient coastlines, marine terraces and recent deposits of three different active tectonic basins in central and Southern Italy. The combination of the modeling of these fault-related landscape features with historical and seismological data better constrained the geometry of the seismogenic faults responsible for three large magnitude historical events in the studied areas. The results show that in this section of the peninsula seismogenesis is often connected with blind almost pure dip-slip normal faults; the long-term activity of these faults produces intermontane basins or coastal plains that are sinking relative to the surrounding areas; the application of this methodology emphasises the importance of geological and geomorphological studies for the recognition of seismogenic faults and for a complete assessment of the seismic hazard in Italy.