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Readily available interferometric data (InSAR) of the coseismic deformation field caused by recent seismic events clearly show that major earthquakes produce crustal deformation over wide areas, possibly resulting in significant stress loading/unloading of the crust. Such stress must be considered in the evaluation of seismic hazards of nuclear power plants (NPP) and, in particular, for the potential of surface slip (i.e., probabilistic fault displacement hazard analysis - PFDHA) on both primary and distributed faults. In this study, based on the assumption that slip on pre-existing structures can represent the elastic response of compliant fault zones to the permanent co-seismic stress changes induced by other major seismogenic structures, we propose a three-step procedure to address fault displacement issues and consider possible influence of surface faulting/deformation on vibratory ground motion (VGM). This approach includes: (a) data on the presence and characteristics of capable faults, (b) data on recognized and/or modeled co-seismic deformation fields and, where possible, (c) static stress transfer between source and receiving faults of unknown capability. The initial step involves the recognition of the major seismogenic structures nearest to the site and their characterization in terms of maximum expected earthquake and the time frame to be considered for determining their “capability” (as defined in the International Atomic Energy Agency - IAEA Specific Safety Guide SSG-9). Then a GIS-based buffer approach is applied to identify all the faults near the NPP, possibly influenced by the crustal deformation induced by the major seismogenic structures. Faults inside these areas have to be tested for “capability” according to the same time window defined for the primary seismogenic structures. If fault capability is confirmed or, eventually, cannot be assessed, the next step is to implement an approach based on the potential to affect the safety of the NPP site in terms of fault geometry, and potential displacement. Finally, in the case where the fault can affect the safety of the site, the third step is the PFDHA or, in other words, the calculation of the annual probability of exceedance of the potential co-seismic fault displacement; this displacement is to be compared with the fault displacement threshold that will impact the safety of the NPP site. We also consider the effect of site vicinity tectonism on site vibratory ground motion and discuss an example in the light of the use of the GMPE.

The review of all available contemporary documents, i.e., technical and photographic reports, newspapers, and other archive material, of the 1908, M 7.1, Messina–Reggio Calabria earthquake has allowed to recognize and classify a large number (365) of independent environmental effects of the earthquake and the subsequent tsunami. The effects have been categorized as slope movement, ground settlement, ground vertical movement and coastal retreat, liquefaction, ground crack, hydrological anomaly, gas emission, light, and rumble. No undisputable evidence of surface faulting has been pointed out. Nevertheless, the widespread and rather homogeneous subsidence of the coastal area of Messina (40–70 cm) might have been caused by slip along a NNE–SSW-trending, east-dipping fault, corresponding to the here proposed Messina Lineament. Likewise, slips along the Reggio Calabria, Armo and Motta San Giovanni faults, suggested by coastal subsidence and slides, ground cracks, and leveling data, cannot be ruled out. A large part of the achieved information has allowed to evaluate the epicentral intensity and local intensities at 74 sites, by applying the environmental seismic intensity scale ESI 2007. This study has led to the most comprehensive picture of the distribution and characteristics of coseismic environmental effects of that earthquake, a crucial knowledge to better estimate the future impact of a similar earthquake on a region that has seen a broad, and often poorly concerned, urban and infrastructural development since then.

Prediction of location and amount of slip for distributed faulting associated to strong earthquakes is a recently explored issue with major implications in terms of hazard assessment. Currently, the best practice involves the applications of Probabilistic Fault Displacement Hazard Analysis (PFDHA) whose results fit sufficiently well real data in the near-range of the primary fault but show considerable inaccuracies in the far-range. We believe that this inaccuracy descends from the biased earthquake databases used for regression analysis, whose data, relative to old earthquakes, were largely collected only by field surveys focused close to the primary fault (i.e., near-range). Remotely-sensed data (i.e., Interferometric Radar Imaging – InSAR) offer the opportunity to precisely measure the surface deformation induced by strong earthquakes and thus to explore its possible relation with distributed faulting. We analyze the L'Aquila earthquake case study (29th April, 2009, Mw 6.3) and explore the correlation between location and slip on distributed faulting and InSAR-derived deformation field. We find a significant correlation between occurrence of distributed faulting and profile curvature of the dislocation field, in spite of the distance from the primary fault. Moreover, distributed faults tend to occur within the area deformed by the earthquake, as imaged by InSAR data and whose extent is directly proportional to the earthquake magnitude (Mw), according to a dataset of 30 recent earthquakes. We then propose that these observations have to be incorporated into the present PFDHA practice as limit boundaries to possible scenarios of probabilistic analysis and that an integrated use of field-based and remotely data collection have to be implemented, following strong earthquakes.

Moderate to strong crustal earthquakes are generally accompanied by a distinctive pattern of coseismic geological phenomena, ranging from surface faulting to ground cracks, landslides, liquefaction/compaction, which leave a permanent mark in the landscape. Therefore, the repetition of surface faulting earthquakes over a geologic time interval determines a characteristic morphology closely related to seismic potential. To support this statement, the areal distribution and dimensions of effects of recent historical earthquakes in the Southern Apennines are being investigated in detail. This paper presents results concerning the 26 July 1805 earthquake in the Molise region, (I =X MCS, M = 6.8), and the 23 November 1980 earthquake in the Campania and Basilicata regions (I =XM SK,Ms = 6.9). Landslide data are also compared with two other historical earthquakes in the same region with similar macroseismic intensity. The number of significant effects (either ground deformation or hydrological anomalies) versus their minimum distance from the causative fault have been statistically analyzed, finding characteristic relationships. In particular, the decay of the number of landslides with distance from fault follows an exponential law, whereas it shows almost a rectilin- ear trend for liquefaction and hydrological anomalies. Most effects fall within the macroseismic area, landslides within intensity V to VI, liquefaction effects within VI and hydrological anomalies within IV MCS/MSK, hence at much larger distances. A possible correlation between maximum distance of effects and length of the reactivated fault zone is also noted. Maximum distances fit the envelope curves for Intensity and Magnitude based on worldwide data. These results suggest that a careful examination of coseismic geological effects can be important for a proper estimation of earthquake parameters and vulnerability of the natural environment for seismic hazard evaluation purposes.

Care must be taken to provide reliable antiseismic protection in earthquake-prone areas where the impact of a large earthquake in megacities with industrial facilities as well as in ordinary buildings is liable to cause massive loss of human life and to cripple the nation's economy. This protection needs to take into account not only vibratory ground motion but also permanent ground failure, and notably surface-faulting hazard, a fact tragically illustrated during the recent events of Turkey and Taiwan. The purpose of this contribution is to conduct a survey of our current state of knowledge concerning theoretical relationships between earthquake source parameters, such as moment magnitude (M, M w), surface wave magnitude ( M S), seismic moment ( M O), stress drop (Δσ), rupture length ( L ), and displacement on the fault ( D ). A relationship is proposed that links M S to L and Δσ: M S = 2 log L + 1.33 log Δσ + 1.66, using a simple rupture model. Earthquake data from all over the world for which the parameters of rupture length, fault width ( W ), fault displacement, and surface-wave magnitude are available have enabled stress drop values to be computed for each event using both geological observation (Δσ1) and the previously proposed equation (Δσ2). The results obtained tend to indicate that stress drop values increase versus fault width (depth) up to approximately 15 km (corresponding perhaps to the brittle-ductile boundary). This increase is more pronounced in the case of reverse faults than it is for those with strike-slip or normal mechanisms. An equation of the type Δσ = kW n has been used to fit the data, and preliminary values for k and n have been supplied for the three slip types. For depths in excess of 15 km the data do not display significant variation (Δσ < 100 bars). These results are in agreement with certain laboratory models of the continental lithosphere. Although more data, particularly in the large-magnitude range, are needed to ascertain whether it is the W or the L model that better describes earthquake scaling laws, stress drop does not appear to be fault-length dependent, thus being supportive of the L model. The risk of surface faulting is dependent on the dynamic environment of the fault, that is, the stress drop, the rupture length, and the fault width. Although statistics show that surface faulting appears in most instances at magnitudes of at least 6.1, data from certain regions indicate that seismicity at superficial depths is under certain conditions accompanied by significant surface faulting even for magnitudes as small as 5.5, suggesting a change in scaling law. The threshold magnitude for surface faulting is accordingly seen to depend on the rheology of materials in the fault area and on the stress environment. Manuscript received 31 May 2000.

The September–October 1997 seismic sequence in the Umbria–Marche regions of Central Italy (main shocks on September 26, Mw 5.7 and 6.0, and on October 14, Mw 5.6) left significant ground effects, which were mainly concentrated in the Colfiorito intermountain basin. These effects included surface faulting, ground cracks and settlements, rock falls, slides, hydrological and gas anomalies. The distribution and size of ground effects has proved useful for (1) defining the epicentral area and the location of the causative fault; (2) complementing the intensity pattern from damage distribution (this can be very useful in poorly inhabited zones); (3) integrating or testing the intensity assessment of many historical events, in order to obtain a better evaluation of the magnitude from intensity data. Of special interest was the observation of surface ruptures generated along segments of a system of normal faults already mapped as capable, with end-to-end lengths of 12 km and maximum displacements of 8 cm. Many pieces of evidence confirm that coseismic slip was not a secondary, gravity-induced, phenomenon, but had a tectonic origin. Detailed descriptions of surface faulting for moderate earthquakes are not common, being easily missed or misinterpreted; however, in this paper we emphasize that surface faulting due to the 1997 event can be used to infer the threshold magnitude for surface faulting in Central Apennines, allowing to calibrate palaeoearthquake size from fault offsets as seen in trench investigations.

Paleoseismology, the study of past earthquakes based on their geological record in the stratigraphy and landscape, is a successful newly developing field of research. The application of fault trench studies in volcanic environments is one of the youngest branches of paleoseismology. In this paper, we present the results of the first exploratory trenches excavated at Mt. Etna in Sicily, the largest European volcano. Modern surface faulting at Etna is a very well known feature, which poses significant hazard to the local community, both in terms of ground displacement of essential lifelines and ground shacking from frequent damaging earthquakes. However, while the geomorphology and the seismicity of the active fault in the Etna region consistently show very high rates of tectonic activity, the Holocene cumulative throw and slip-rates, along with the nature (coseismic vs. creeping fault slip), dimension and timing of the displacement events, are still poorly constrained. For this purpose, we selected as a sample area the Moscarello fault, one of the most outstanding segment of the Timpe system of active normal faults in the volcano’s lower eastern flank. Displaced landforms and volcanic units at the Fondo Macchia basin, in the central sector of this fault, indicate some hundreds of meters of vertical offset in the last ca. 80 kyr, with a long-term slip-rate substantially higher than 1.5–2.0 mm/yr. According to the historical sources and instrumental observations, the Moscarello fault ruptured four times in the last 150 years during shallow (H M s =3.7 , earthquake. The excavated sections provided direct stratigraphic evidence for a vertical slip-rate of 1.4–2.7 mm/yr in the last ca. 6 kyr. This should be regarded as a minimum slip-rate for the central section of the fault. We explored a single scarp at a single site, while we know from recent historical observations that several parallel scarps may rupture coseismically at Fondo Macchia. Thus, the relevant deformation rate documented for the modern period might be likely extended back in the past to a time-span of some thousands of years at least. As expected, for such a volcanic environment, the activity rates of the Moscarello fault are also significantly higher than for the Apennines normal faults, typically showing slip-rates lower than 1 mm/yr. The agriculturally reworked trench hangingwall stratigraphy did not allow to recognize individual displacement events. Nevertheless, the sedimentary structures observed in the trench footwall strongly suggest that, as for the last 150–200 years of detailed historical record, fault behavior at Fondo Macchia is governed by coseismic surface displacement rather than fault creep. This research confirms that paleoseismology techniques can be effectively applied also in active volcanic environments, typically characterized by rheology and, consequently, seismicity and fault dynamics very different from those of other tectonic environments in which paleoseismology has been firstly developed and is today extensively applied.

When dealing with hazard, the concept of fault capability (the probability of significant surface displacement in the near future) is more useful than the generic and often misleading concept of fault activity. The example of the Pernicana fault, located in the north-eastern flank of the Mt. Etna volcano is used here to illustrate the damage which can be expected in an urbanised area from a capable fault, in this case characterized by 'aseismic’ creep along part of its length. Along this fault, buildings, roads and other essential lifelines are being affected by slow, left-lateral displacement. The Pernicana fault is only one of a set of structures in the area whose movement, either connected to seismicity or not, is producing severe damage. First identified at the end of the last century, this source of hazard is, nevertheless, still poorly considered by planners and technicians. In Italy fault creep is quite rare outside the Etna region, but fault capability associated with strong earthquakes is relatively frequent, based on historical and palaeoseismological data, and is a feature that should be taken into account for hazard reduction programs.

Historical seismicity provides only a partial indication of the seismotectonic character (i.e. earthquake potential) of a given region. Even in Italy, where a relatively long historical record exists, available catalogues are generally unsatisfactory for this purpose. Fortunately, strong earthquakes often leave geological evidence, herein referred to as seismites, that are mainly related to surface faulting, folding or other deformation, and occasionally to secondary ground failures (e.g. landslides, liquefaction features, etc.). These features may be preserved and, therefore, palaeoseismological studies may detect and date them, thereby permitting extension of knowledge beyond the local historical threshold (up to 2000 years in the most fortunate cases). This paper provides a summary of criteria which may aid in the identification of areas suitable for palaeo-earthquake investigation. Historical seismicity and the presence of well developed tectonic geomorphic features are recognized as the most reliable criteria for identifying active faulting. However, lack of these characteristics cannot be considered conclusive evidence for lack of activity. Palaeoseismological techniques aim at identifying not only the obvious effects of surface faulting, such as offset of young geologic units, but also the more subtle tectonic or non-tectonic features, including liquefaction structures, gravity features and coseismic uplift and/or subsidence. Finally, we discuss some questions that pertain to palaeoseismicity evaluation techniques. Among these are the reliability of the Quaternary dating techniques, the evaluation of the seismic energy released (minimum magnitude) and principally, the unequivocal identification of a seismic origin for the considered geological structures.

The Pollino Range is the southernmost segment of the Southern Apennines at the boundary with the Calabrian Arc. While several strong earthquakes (magnitude 6.5–7.0) have occurred in nearby regions, the Pollino area has no known historical record of seismic events of magnitude > 5. We carried out an aerial photograph interpretation and a field survey of the Pollino fault (the major Quaternary normal fault of the area) in order to characterize geologically the seismic potential of this structure. We dug two sets of trenches across fault scarps within the apecies of latest Pleistocene to Holocene alluvial fans at the Masseria Quercia Marina (MQM) and Grotta Carbone (GC) sites, in the central segment of the southern Pollino Range front. At both sites we identified two surface faulting events affecting the alluvial fan deposits and two overlying colluvial units of historical age. The penultimate event produced a vertical offset of 80–90 cm at GC and 50–60 cm at MQM; while the last event produced a vertical offset of 40–50 cm at GC and few centimeters of offset at MQM. Detailed geomorphological field observations suggest that the two historical earthquakes reactivated the entire length of the Masseria Marzano-Civita segment of the Pollino fault (rupture length about 18 km). For events in this range of rupture length and vertical displacement, comparison with surface faulting earthquakes in the Apennines (and abroad) indicates a magnitude of 6.5–7.0. Therefore, the maximum potential earthquake and the seismic hazard of the Pollino area are significantly larger than that suggested by the available historical seismic catalogue.

Earthquake hazard analyses in Italy are mainly based on historical seismic catalogs. However, the completeness of the Italian catalog, which spans more than 2000 years, progressivcly decreases going back in time. In the Fucino basin, historical research has not produced evidence of large earthquakes before the January 13, 1915, event (M s = 7.0 ; 33,000 people killed). This event generated surface faulting along at least two parallel Quaternary normal faults bounding the eastern side of the basin (the Celano-Gioia and Parasano-Cerchio faults), over an end-to-end length of about 23 km, with a downthrow of 30-90 cm toward southwest. To improve geological aspects of the seismic history of this area, we trenched onc of the coseismic scarps along the Celano-Gioia fault. At a trench site, near the village of San Benedetto de' Marsi, the fault traverses the area formerly covered by the Fucino Lake, drained for farming in 1875 A.D. The evidence collected in the trenchcs suggests at least two large events in historical times before 1915. Radiocarbon dates constrain the age of event B between the 6th and the 9th centuries A.D., possibly coinciding with the cvent felt in Rome in 801 A.D. [Molin arid Guidoboni, 1989]. Event A probably occurred after the 10th ccntury A.D. and almost certainly before the 1349 A.D. earthquake, because historical studies show (1) that event A was not produced during the earthquake sequence that occurred in central Italy in 1349 A.D. [Molin and Guidoboni, 1989] and (2) that the post-1349 seismic catalog can be regarded as complete for surface faulting earthquakes. Surface displacements determined for events A and B, compared to the 1915 surface faulting, indicate that M > 6.5 earthquakes were associated with each rupturc. These obscrvations suggest that the return period for large earthquakes in the Fucino basin is shorter than that indicated by the historical record alone. The Fucino example clearly shows that thc cxceptionally long historical record in Italy is still inadequate for a comprehcnsive seismic hazard characterization.