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 ( ...https://doi.org/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.
There is growing interest in how geofluid emissions are released in the atmosphere by the planet’s geodynamic activity, and how much they contribute to the global budget of greenhouse gases. Many ...workers are addressing this issue with studies conducted at global scale, so as to get the required global-scale answers. The data available at the global scale on geofluids, faults, earthquakes and volcanoes, however, are generally too coarse to provide these answers. We investigate the relationships between geofluid emissions and tectonics at a more detailed scale. Building on over a century of data on geofluid emissions and on an extensive knowledge of the region’s tectonics and seismicity, we focused on Italy, one of the areas of the globe that experience the largest release of natural CO
2
and CH
4
. We systematically overlaid and compared data collected by a number of workers into 13 published countrywide databases concerning geofluid emissions, carbon-bearing deposits, seismogenic faults, historical and instrumentally documented earthquakes, and heat flow observations. Our results indicate that 1) thermal springs and CO
2
emissions dominate in areas of mantle upwelling and crustal stretching, but also that 2) some of them occur in the extending inner Apennines, generally along major lithospheric chain-perpendicular lineaments that bound the largest normal faults. Conversely, 3) CH
4
emissions and mud volcanoes dominate in areas undergoing active contraction, where no CO
2
emissions are observed; in particular, we find 4) that mud volcanoes concentrate where the crests of active anticlines intersect major lithospheric chain-perpendicular lineaments. An overarching conclusion is that, in Italy, the release of geofluids is primarily controlled by deep crustal discontinuities that developed over the course of 5–10 My, and is only mildly affected by ongoing crustal strains. Geofluid emissions bring information on processes that occur primarily in the lower crust, marking the surface projection of generally hidden discontinuities that control the geometry and modes of seismic release. As such they may also provide valuable insight for improving the assessment of seismic hazard in hard-to-investigate seismically active regions, such as Italy.
We use wet-clay analog models to investigate how pre-existing discontinuities (i.e. structures inherited from previous tectonic phases) affect the evolution of a normal fault at the Earth's surface. ...To this end we first perform a series of three reference experiments driven by a 45° dipping master fault unaffected by pre-existing discontinuities to generate a mechanically isotropic learning set of models. We then replicate the experiment six times introducing a 60°-dipping precut in the clay cake, each time with a different attitude and orientation with respect to an initially-blind, 45°-dipping, master normal fault. In all experiments the precut intersects the vertical projection of the master fault halfway between the center and the right-hand lateral tip. All other conditions are identical for all seven models. By comparing the results obtained from the mechanically isotropic experiments with results from experiments with precuts we find that the surface evolution of the normal fault varies depending on the precut orientation. In most cases the parameters of newly-forming faults are strongly influenced. The largest influence is exerted by synthetic and antithetic discontinuities trending respectively at 30° and 45° from the strike of the master fault, whereas a synthetic discontinuity at 60° and an antithetic discontinuity at 30° show moderate influence. Little influence is exerted by a synthetic discontinuity at 45° and an antithetic discontinuity at 60° from the strike of the master fault. We provide a ranking chart to assess fault-to-discontinuity interactions with respect to essential surface fault descriptors, such as segmentation, vertical-displacement profile, maximum displacement, and length, often used as proxies to infer fault properties at depth. Considering a single descriptor, the amount of deviation induced by different precuts varies from case to case in a rather unpredictable fashion. Multiple observables should be taken into consideration when analyzing normal faults evolving next to pre-existing discontinuities.
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•We use wet-clay analog models to simulate isolated initially-blind normal faults.•We analyze the interaction of surface normal faults with inherited discontinuities.•Inherited discontinuities strongly affect fault development at the Earth's surface.•The influence of a discontinuity strongly depends on its orientation relative to the fault.•We provide a ranking chart to assess fault-to-discontinuity interactions.
We calculated the impact on Southern Italy of a large set of tsunamis resulting from earthquakes generated by major fault zones of the Mediterranean Sea. Our approach merges updated knowledge on the ...regional tectonic setting and scenario‐like calculations of expected tsunami impact. We selected three potential source zones located at short, intermediate and large distance from our target coastlines: the Southern Tyrrhenian thrust belt; the Tell‐Atlas thrust belt; and the western Hellenic Arc. For each zone we determined a Maximum Credible Earthquake and described the geometry, kinematics and size of its associated Typical Fault. We then let the Typical Fault float along strike of its parent source zone and simulated all tsunamis it could trigger. 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 desired simulation times and the maximum water elevation field, then produced traveltime maps and maximum wave‐height profiles along the target coastlines. The results show a highly variable impact for tsunamis generated by the different source zones. For example, a large Hellenic Arc earthquake will produce a much higher tsunami wave (up to 5 m) than those of the other two source zones (up to 1.5 m). This implies that tsunami scenarios for Mediterranean Sea countries must necessarily be computed at the scale of the entire basin. Our work represents a pilot study for constructing a basin‐wide tsunami scenario database to be used for tsunami hazard assessment and early warning.
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. ...
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. 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.
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. …
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.
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.
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