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  • 1
    Electronic Resource
    Electronic Resource
    Testing a new hybrid approach to seismic hazard assessment: an application to the Calabrian Arc (Southern Italy) (1996)
    Springer
    Natural hazards 14 (1996), S. 113-126 
    Details
    ISSN: 1573-0840
    Keywords: seismic hazard ; characteristic earthquake ; time dependent process ; Calabria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract We tested a new hybrid method for the evaluation of seismic hazard. A recently proposed fault segmentation and earthquake recurrence model of peninsular Italy suggests that the interval for which the local historical catalogue is complete is shorter than the mean recurrence time of individual large faults (∼1000 years), or at the most comparable. These new findings violate the fundamental assumption of historical probabilistic seismic hazard methods that the historical record is representative of the activity of all the seismogenic sources. The hybrid method we propose uses time-dependent modelling of the major earthquakes and catalogue-based historical probabilistic estimates for all minor events. We assume that the largest earthquakes are characteristic for individual discrete fault segments, model their probability of occurrence by a renewal process and compute the shaking associated with each of them with a simplified procedure. Then we calculate the probability of exceeding a given threshold of peak ground acceleration for specific sites as the aggregate probability of occurrence of large characteristic earthquakes and minor shocks. We apply the method to the Calabrian Arc (Southern Italy) performing the calculations for five major towns. The exposure to seismic hazard of Reggio Calabria, Catanzaro and Vibo Valentia, which locate close to recently activated large faults, decreases with respect to traditional time-independent estimates. On the contrary, an increase of seismic hazard is obtained for Castrovillari, which locates in an area where large faults displaying Holocene activity have been recently recognized but no significant earthquake is reported in the historical catalogue. Cosenza has the highest probability to experience a significant peak ground acceleration with both the new hybrid and the traditional approaches. We wish to stress that the present results should be interpreted only in terms of the differences between the new hybrid and the traditional approaches, not for their absolute values, and that they are not intended to be used for updating or modifying the current national seismic zonation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00128260
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    Paper (German National Licenses)
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  • 2
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    Shallow subsurface imaging of the Piano di Pezza active normal fault (central Italy) by high-resolution refraction and electrical resistivity tomography coupled with time-domain electromagnetic data (2015)
    Oxford University Press
    Details
    Publication Date: 2015-10-22
    Description: The Piano di Pezza fault is the central section of the 35 km long L'Aquila-Celano active normal fault-system in the central Apennines of Italy. Although palaeoseismic data document high Holocene vertical slip rates (~1 mm yr –1 ) and a remarkable seismogenic potential of this fault, its subsurface setting and Pleistocene cumulative displacement are still poorly known. We investigated for the first time the shallow subsurface of a key section of the main Piano di Pezza fault splay by means of high-resolution seismic and electrical resistivity tomography coupled with time-domain electromagnetic soundings (TDEM). Our surveys cross a ~5-m-high fault scarp that was generated by repeated surface-rupturing earthquakes displacing Holocene alluvial fans. We provide 2-D Vp and resistivity images, which show significant details of the fault structure and the geometry of the shallow basin infill material down to 50 m depth. Our data indicate that the upper fault termination has a sub-vertical attitude, in agreement with palaeoseismological trench evidence, whereas it dips ~50° to the southwest in the deeper part. We recognize some low-velocity/low-resistivity regions in the fault hangingwall that we relate to packages of colluvial wedges derived from scarp degradation, which may represent the record of some Holocene palaeo-earthquakes. We estimate a ~13–15 m throw of this fault splay since the end of the Last Glacial Maximum (~18 ka), leading to a 0.7–0.8 mm yr –1 throw rate that is quite in accordance with previous palaeoseismic estimation of Holocene vertical slip rates. The 1-D resistivity models from TDEM soundings collected along the trace of the electrical profile significantly match with 2-D resistivity images. Moreover, they indicate that in the fault hangingwall, ~200 m away from the surface fault trace, the pre-Quaternary carbonate basement is at ~90–100 m depth. We therefore provide a minimal ~150–160 m estimate of the cumulative throw of the Piano di Pezza fault system in the investigated section. We further hypothesize that the onset of the Piano di Pezza fault activity may date back to the Middle Pleistocene (~0.5 Ma), so this is a quite young active normal fault if compared to other mature normal fault systems active since 2–3 Ma in this portion of the central Apennines.
    Keywords: Geodynamics and Tectonics
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 3
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    The L'Aquila trial (2015)
    Geological Society (of London)
    Details
    Publication Date: 2015-02-15
    Description: The first stage of the trial in L'Aquila (Italy) ended with a conviction of seven experts, convened by the head of Civil Protection on 31 March 2009, for multiple manslaughter and serious injuries. They were sentenced to six years in jail, perpetual interdiction from public office and a fine of several million euros to be paid to the victims of the earthquake of 6 April 2009 (moment magnitude 6.3) for having caused, by their negligent conduct, the death of 29 persons and the injury of several others. The verdict had a tremendous impact on the scientific community and on the way scientists deliver their expert opinions to decision makers and society. This paper analyses the scientific argumentations reported in the Verdict Motivations, where scientific data and results were largely debated and misused to demonstrate that they should have been considered as a tool to predict an impending large earthquake. Moreover, we show that the supposed message of reassurance was not generated at the experts’ meeting or by the official Istituto Nazionale di Geofisica e Vulcanologia reports. The media had a key role in conveying information during the seismic swarm, contributing to the risk perception. We stress that prevention actions based on seismic hazard knowledge are the best defence against earthquakes.
    Print ISSN: 0305-8719
    Electronic ISSN: 2041-4927
    Topics: Geosciences
    Published by Geological Society (of London)
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  • 4
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    Integrating multidisciplinary, multiscale geological and geophysical data to image the Castrovillari fault (Northern Calabria, Italy) (2015)
    Oxford University Press
    Details
    Publication Date: 2015-10-30
    Description: The Castrovillari scarps (Cfs) are located in northern Calabria (Italy) and consist of three main WSW-dipping fault scarps resulting from multiple rupture events. At the surface, these scarps are defined by multiple breaks in slope. Despite its near-surface complexity, the faults likely merge to form a single normal fault at about 200 m depth, which we refer to as the Castrovillari fault. We present the results of a multidisciplinary and multiscale study at a selected site of the Cfs with the aim to (i) characterize the geometry at the surface and at depth and (ii) obtain constraints on the fault slip history. We investigate the site by merging data from quantitative geomorphological analyses, electrical resistivity and ground penetrating radar surveys, and palaeoseismological trenching along a ~40 m high scarp. The closely spaced investigations allow us to reconstruct the shallow stratigraphy, define the fault locations, and measure the faulted stratigraphic offsets down to 20 m depth. Despite the varying resolutions, each of the adopted approaches suggests the presence of sub-parallel fault planes below the scarps at approximately the same location. The merged datasets permit the evaluation of the fault array (along strike for 220 m within a 370-m-wide zone). The main fault zone consists of two closely spaced NW–SE striking fault planes in the upper portion of the scarp slope and another fault at the scarp foot. The 3-D image of the fault surfaces shows west to southwest dipping planes with values between 70° and 80°; the two closely spaced planes join at about 200 m below the surface. The 8-to-12-m-high upper fault, which shows the higher vertical displacements, accommodated most of the deformation during the Holocene. Results from the trenching analysis indicate a minimum slip per event of 0.6 m and a maximum short-term slip rate of 0.6 mm yr –1 for the Cf. The shallow subsurface imaging techniques are particularly helpful in evaluating the possible field uncertainties related to postfaulting modification by erosional/depositional/human processes, such as within stream valleys and urbanized zones.
    Keywords: Geodynamics and Tectonics
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 5
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    A Ten-Year Earthquake Occurrence Model for Italy (2012)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2012-06-01
    Description: The recent Mw 6.3 destructive L’Aquila earthquake has further stimulated the improvement of the Italian operational earthquake forecasting capability at different time intervals. Here, we describe a medium-term (10-year) forecast model for Mw≥5.5 earthquakes in Italy that aims at opening new possibilities for risk mitigation purposes. While a longer forecast yielded by the national seismic-hazard map is the primary component in establishing the building code, a medium-term earthquake forecast model may be useful to prioritize additional risk mitigation strategies such as the retrofitting of vulnerable structures. In particular, we have developed an earthquake occurrence model for a 10-year forecast that consists of a weighted average of time-independent and different types of available time-dependent models, based on seismotectonic zonations and regular grids. The inclusion of time-dependent models marks a difference with the earthquake occurrence model of the national seismic-hazard map, and it is motivated by the fact that, at the 10-year scale, the contribution of time-dependency in the earthquake occurrence process may play a major role. The models are assembled through a simple averaging scheme whereby each model is weighted through the results of a retrospective testing phase similar to the ones carried out in the framework of the Collaboratory for the Study of Earthquake Predictability. In this way, the most hazardous Italian areas in the next ten years will arise from a combination of distinct models that place more emphasis on different aspects of the earthquake occurrence process, such as earthquake clustering, historical seismic rate, and the presence of delayed faults capable of large events. Finally, we report new challenges and possible developments for future updating of the model.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 6
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    Deriving a long paleoseismic record from a shallow-water Holocene basin next to the Alpine fault, New Zealand (2013)
    Geological Society of America (GSA)
    Details
    Publication Date: 2013-05-03
    Description: A sedimentary sequence that was highly sensitive to fault rupture–driven changes in water level and sediment supply has been used to extract a continuous record of 22 large earthquakes on the Alpine fault, the fastest-slipping fault in New Zealand. At Hokuri Creek, in South Westland, an 18 m thickness of Holocene sediments accumulated against the Alpine fault scarp from ca. A.D. 800 to 6000 B.C. We used geomorphological mapping, sedimentology, and paleoenvironmental reconstruction to investigate the relationship between these sediments and Alpine fault rupture. We found that repeated fault rupture is the most convincing mechanism for explaining all the features of the alternating peat and silt sedimentary sequence. Climate has contributed to sedimentation but is unlikely to be the driver of these cyclical changes in sediment type and paleoenvironment. Other nontectonic causes for the sedimentary alternations do not produce the incremental increase in basin accommodation space necessary to maintain the shallow-water environment for 6800 yr. Our detailed documentation of this near-fault sedimentary basin sequence highlights the advantages of extracting paleoearthquake records from such sites—the continuity of sedimentation, abundance of dateable material, and pristine preservation of older events.
    Print ISSN: 0016-7606
    Electronic ISSN: 1943-2674
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 7
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    Investigating the architecture of the Paganica Fault (2009 Mw 6.1 earthquake, central Italy) by integrating high-resolution multiscale refraction tomography and detailed geological mapping (2016)
    Oxford University Press
    Details
    Publication Date: 2016-11-25
    Description: We present a 2-D subsurface image of the Paganica Fault from a high-resolution refraction tomography and detailed geological investigation carried out across part of the northwestern segment of the 20-km-long Paganica–San Demetrio fault-system, and which was responsible of the 2009 April 6 M w 6.1 L'Aquila earthquake (central Italy). We acquired two seismic profiles crossing the Paganica basin with a dense-wide aperture configuration. More than 30 000 P wave first-arrival traveltimes were input to a non-linear tomographic inversion. The obtained 250–300 m deep 2-D Vp images illuminate the shallow portion of the Paganica Fault, and depict additional unreported splays defining a complex half-graben structure. We interpret local thickening of low- Vp (〈2400 m s –1 ) and intermediate- Vp (2600–3400 m s –1 ) regions as syn-tectonic clastic wedges above a high- Vp (3800–5000 m s –1 ) carbonate basement. These results are condensed in a 4.2-km-long section across the Paganica basin, clearly indicating that the Paganica Fault is a mature normal fault cutting the whole upper ~10 km of the crust. We evaluate a minimum cumulative net displacement of 650 ± 90 m and a total heave of 530 ± 65 m accomplished by the Paganica Fault, respectively. In the conservative hypothesis that the extension started during the Gelasian (1.80–2.59 Ma), we obtain a minimum long-term slip-rate of 0.30 ± 0.07 mm yr –1 and an extension-rate of 0.25 ± 0.06 mm yr –1 , respectively. Considering the regional averaged extensional field of ~1 mm yr –1 obtained from geodetic and geological analyses at 10 4  yr timescale, we infer that the Paganica Fault accounts for ~20 per cent of the NE-extension affecting this zone of the central Apennines axis due to the concurrent activity of other parallel normal fault-systems nearby (e.g. the Liri, Velino-Magnola, L'Aquila-Celano and Gran Sasso fault-systems).
    Keywords: Geodynamics and Tectonics
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 8
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    Deep electrical resistivity tomography along the tectonically active Middle Aterno Valley (2009 L'Aquila earthquake area, central Italy) (2016)
    Oxford University Press
    Details
    Publication Date: 2016-09-24
    Description: Three 2-D Deep Electrical Resistivity Tomography (ERT) transects, up to 6.36 km long, were obtained across the Paganica-San Demetrio Basin, bounded by the 2009 L'Aquila M w 6.1 normal-faulting earthquake causative fault (central Italy). The investigations allowed defining for the first time the shallow subsurface basin structure. The resistivity images, and their geological interpretation, show a dissected Mesozoic-Tertiary substratum buried under continental infill of mainly Quaternary age due to the long-term activity of the Paganica-San Demetrio normal faults system (PSDFS), ruling the most recent deformational phase. Our results indicate that the basin bottom deepens up to 600 m moving to the south, with the continental infill largely exceeding the known thickness of the Quaternary sequence. The causes of this increasing thickness can be: (1) the onset of the continental deposition in the southern sector took place before the Quaternary, (2) there was an early stage of the basin development driven by different fault systems that produced a depocentre in the southern sector not related to the present-day basin shape, or (3) the fault system slip rate in the southern sector was faster than in the northern sector. We were able to gain sights into the long-term PSDFS behaviour and evolution, by comparing throw rates at different timescales and discriminating the splays that lead deformation. Some fault splays exhibit large cumulative throws (〉300 m) in coincidence with large displacement of the continental deposits sequence (〉100 m), thus testifying a general persistence in time of their activity as leading splays of the fault system. We evaluate the long-term (3–2.5 Myr) cumulative and Quaternary throw rates of most of the leading splays to be 0.08–0.17 mm yr –1 , indicating a substantial stability of the faults activity. Among them, an individual leading fault splay extends from Paganica to San Demetrio ne’ Vestini as a result of a post-Early Pleistocene linkage of two smaller splays. This 15 km long fault splay can explain the Holocene surface ruptures observed to be larger than those occurred during the 2009 L'Aquila earthquake, such as revealed by palaeoseismological investigations. Finally, the architecture of the basin at depth suggests that the PSDFS can also rupture a longer structure at the surface, allowing earthquakes larger than M 6.5, besides rupturing only small sections, as it occurred in 2009.
    Keywords: Geodynamics and Tectonics
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 9
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    Imaging the structural style of an active normal fault through multidisciplinary geophysical investigation: a case study from the Mw 6.1, 2009 L'Aquila earthquake region (central Italy) (2015)
    Oxford University Press
    Details
    Publication Date: 2015-02-06
    Description: The normal fault-system responsible of the 2009 M w 6.1 L'Aquila earthquake (Paganica-San Demetrio fault-system) comprises several narrow, fault-parallel valleys of controversial origin. We investigated a key section of the southeastern portion of this fault network along the small Verupola Valley. In order to characterize its nature and possible tectonic activity, we applied multiple-geosciences techniques able to image at depth the structure associated to this peculiar landform. We integrated magnetometry, 2-D P wave and resistivity tomography, surface waves and seismic noise analysis coupled with field mapping, shallow boreholes and trenching. According to our results, the Verupola Valley is a ~30–40-m-deep graben controlled by a SW-dipping master fault and synthetic splays paired with an antithetic NE-dipping fault. The SW-dipping splays are active and cut very shallow (〈2 m deep) Late Pleistocene sediments. The small amount of cumulated vertical offset (~15 m) across the conjugated system may indicate a young fault inception or very low Quaternary slip-rates. Due to its structural continuity with the adjacent mapped strands of the Paganica–San Demetrio fault network, we relate the Verupola Valley to the recent activity of the southeastern segment of this fault system. We also suggest that other fault-parallel valleys can have the same tectonic origin and setting of the Verupola Valley. This latter represents a scale-independent analogue from metric scale (exposed in the palaeoseismological trenches) to the Middle Aterno Basin scale (seen from seismic profiles and fault mapping). Overall, the imaged structural style is coherent with the regional tectonic setting due to Quaternary crustal extension.
    Keywords: Geodynamics and Tectonics
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 10
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    Paleoseismic Investigation of Historical Liquefactions Along the Ionian Coast of Sicily (2008)
    Taylor & Francis
    Details
    Publication Date: 2008-12-17
    Print ISSN: 1363-2469
    Electronic ISSN: 1559-808X
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Published by Taylor & Francis
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