A contribution to seismic hazard assessment of the Salento Peninsula (Apulia, Southern Italy) (original) (raw)
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Natural Hazards, 2016
The aim of this study was to provide a contribution to seismic hazard assessment of the Salento Peninsula (Apulia, southern Italy). It is well known that this area was struck by the February 20, 1743, earthquake (I 0 = IX and M w = 7.1), the strongest seismic event of Salento, that caused the most severe damage in the towns of Nardò (Lecce) and Francavilla Fontana (Brindisi), in the Ionian Islands (Greece) and in the western coast of Albania. It was also widely felt in the western coast of Greece, in Malta Islands, in southern Italy and in some localities of central and northern Italy. Moreover, the area of the Salento Peninsula has also been hit by several low-energy and a few high-energy earthquakes over the last centuries; the instrumental recent seismicity is mainly concentrated in the western sector of the peninsula and in the Otranto Channel. The Salento area has also experienced destructive seismicity of neighboring regions in Italy (the Gargano Promontory in northern Apulia, the Southern Apennines chain, the Calabrian Arc) and in the Balkan Peninsula (Greece and Albania). Accordingly, a critical analysis of several documentary and historical sources, as well as of the geologic-geomorphologic ground effects due to the strong 1743 Salento earthquake, has been carried out by the authors in this paper; the final purpose has been to re-evaluate the 1743 MCS macroseismic intensities and to provide a list of newly classified localities according to the ESI-07 scale on the base of recognized Earthquake Environmental Effects. The result is a quite different damage scenario due to this earthquake that could raise the seismic potential currently recognized for the Salento area, and consequently upgrade the seismic hazard classification of the Salento. Indeed it is important to remind that currently, despite the intense earthquake activity recorded not only in the Otranto Channel, but especially in Greece and Albania, this area is classified in the least dangerous category of the Seismic Classification of the Italian territory (IV category).
The Apulia (Southern Italy) has been hit by several low energy and a few high energy earthquakes from 17th to 19th century. The aim of this study is a critical revision of the historical and recent seismicity of the Apulian region and surrounding seismogenetic areas, for re-evaluating the macroseismic effects in MCS scale and ground effects in natural environment according to the ESI 2007 scale (Michetti et al., 2007; Guerrieri et al., 2015). In particular, the February 20, 1743 earthquake, the strongest of the Salento area and the July 30, 1627 earthquake, the strongest of the Gargano promontory have been reviewed. Moreover we have evaluated the most important effects on land in the Salento and Gargano area. The use of both traditional MCS macroseismic intensity scale and the ESI 2007 scale gives a more accurate image of the earthquakes (Porfido et al., 2007) and allowed us to better constrain the seismic hazard assessment in the Salento peninsula.
2014
Introduction. The area of the Salento peninsula (Apulia, Southern Italy) is considered the stable foreland of the Southern Apennines chain (Cinque et al., 1993), although it has been hit by several low energy and a few high energy earthquakes over the last centuries. The aim of this study is a critical revision of the historical and recent seismicity of the Salento peninsula and surrounding seismogenetic areas, for re-evaluating the macroseismic effects in MCS scale and ground effects in natural environment, according to the ESI 2007 scale (Michetti et al., 2007; Guerrieri et al., 2012). In particular, the February 20, 1743 earthquake, the strongest of the area, was reviewed and new MCS intensity values were attributed to some localities. Moreover we have evaluated the most important effects on land in the Salento area due to the strong earthquakes of Northern Apulia, Southern Apennines, Adriatic and Ionian sea, Albania and Greece. The use of both traditional MCS macroseismic intensity scale and the ESI 2007 scale gives a more accurate image of the earthquake (Dengler and McPherson, 1993; Porfido et al., 2007; Serva et al., 2007) and allowed us to better constrain the seismic hazard assessment in the Salento peninsula. Geodynamic background. The central area of the Mediterranean basin is a plate-boundary region of high seismicity and complex tectonics, dominated by frequent earthquake activity occurring mostly in the Ionian Sea and Western Greece. The Apulia region, NW-SE elongated, represents the emerged part of the Adriatic foreland domain shared by the Apennine chain to the west, and the Dinaride-Hellenide chain to the east (Moretti and Royden, 1988). The geodynamic background of this area is characterized by the ongoing subduction of the Ionian slab beneath the Calabrian Arc (Caputo et al., 1970), such compressional regime is still active and outlined by relevant seismicity (Castello et al., 2006). As regards the tectonic setting of the Apennine-Dinaride converging region and surroundings, according to Gambini and Tozzi (1996) the major structural lineaments to be considered are: the Scutari-Pec Line; the Pescara-Dubrovnik dextral shear Line; the North Gargano Fault Zone; the Mattinata Gondola Fault Zone; the South Salento-North Kerkira Fault Zone; the right-lateral Cephalonia Transform Fault (see map in Gambini and Tozzi, 1996). The rigid Apulian foreland block has been deformed through several normal faults, NW-SE and NNW-SSE trending, some of them presently active since they dislocate the sea floor by about 200-300 m (Merlini et al., 2000); moreover, major E-W strike-slip and oblique-slip fault zones divide Apulia into structural blocks behaving independently, among them the Gargano Promontory, the Murge Ridge and the Salento Peninsula are relevant. In particular, the Salento peninsula represents the southernmost part of the Apulia foreland. The outcropping rocks are prevalently limestone-dolomite units belonging to the Apulia platform, with carbonatic-terrigenous marine deposits at the top of the stratigraphic sequence, Middle Eocene-Upper Pleistocene age (Mastronuzzi et al., 2011). The Salento peninsula has undergone a general uplift since Middle Pleistocene, with total amount of about 150 meters; after this period and in more recent times, neotectonic data indicate a significant stability of this area.
The ‘‘taranta’’effect of the 1743 earthquake in Salento (Apulia, southern Italy)
2008
The Salento Peninsula (Apulia, southern Italy), along with a few other regions in Italy, is traditionally considered a low seismic hazard area. However, in 1743 it was affected by the catastrophic effects (I max =IX-X MCS) of an earthquake, that probably occurred offshore, in the Salento Plateau (Ionian Sea). Subsequent damage had a complex pattern, whereby some towns were almost razed to the ground and others, nearby, suffered only slight damage. By means of an integrated geological, geotechnical and geophysical analysis we tried to cast a light on the causes of this peculiar distribution of seismic shaking, which we finally modelled by means of a one-dimensional simulation. These results, together with the re-analysis of the macroseismic distribution of the earthquake, and the seismotectonic knowledge of the region, suggest that the 1743 event was a strong, deep one that occurred far from Salento. The event induced high amplification, mainly in the villages (i.e., Nardò and Francavilla Fontana) founded on thin Pleistocene basins filled with soft sediments. The highest amplification peak, due to both the spectral content of the earthquake, as well as to the resonant period of the sedimentary basins, occurred in the same frequency range as most of the buildings of the time, that is ~3 Hz. This terrific double-resonance effect seems to be the main cause for the highest intensity evaluated in Salento, which, would otherwise, have been struck by effects possibly close to VII-VIII MCS.
An attempt to evaluate seismic hazard in Central-Southern Italy
Natural Hazards, 1990
A method for the evaluation of seismic hazard in a given zone, taking into account both the spreading of macroseismic effects and seismic catalogue information, is applied. A databank of some 500 digitized isoseisms of earthquakes having occurred in Italy between 1542 and 1986 is used. The isoseismical maps are digitized considering for each degree of intensity the length of 24 spreading rays starting from the macroseismic epicenter or barycentre of the megaseismic area. These rays are separated from each other by the same angle, i.e. every isoseism is divided into 24 equal circular sectors. The year 1542 is taken as the beginning of the time span, since this is when the first seismic event occurred for which reliable isoseismal maps are available. The epicentral intensities considered lie between the VI and XI degrees of the Mercalli-Cancani-Sieberg scale (MCS). This digitized databank is analyzed to achieve, for each homogeneous seismogenetic zone that has been recognized, the mean azimuthal spreadings of effects for each degree of intensity as a function of the epicentral intensity. Once a mean propagation model is obtained for each zone, this is applied to seismic events of the same zone, the isoseismal maps of which are not available. A geographic grid is defined to cover the analyzed area, and for each cell of this grid it is then possible to count the number of felt events and their degree. These effects have been evaluated either on the basis of the isoseismal maps (when available) or on the basis of the mean propagations of the zone in which the single event occurred. Moreover, an index summarizing the seismic information was computed for each cell of the previous grid. All the events producing effects and their provenance are stored on files, allowing the main seismogenic zones influencing this cell to be identified. This methodology has been applied to central and southern Italy in an area between the latitudes 40.6 and 43.3 N. In particular, attention is focussed on the sample areas of Rome (given the historical and political importance of the city) and of the Sannio-Matese and Irpinia zone (in which some of the strongest earthquakes of the Apennine chain have occurred). Finally, in order to evaluate the maximum expected magnitude, extreme value statistics (Gumbel III-type) are applied to the Colli Albani area, which represents the seismogenic zone nearest to Rome. For the Sannio-Matese and Irpinia area, considering the more dangerous zone as a 'unicum', the Weibull distribution has been hypothesized to determine the mean return time for events with an intensity greater than or equal to IX.
The "taranta 1 " effect of the 1743 earthquake in Salento (Apulia, southern Italy)
Bollettino Di Geofisica Teorica Ed Applicata, 2008
The Salento Peninsula (Apulia, southern Italy), along with a few other regions in Italy, is traditionally considered a low seismic hazard area. However, in 1743 it was affected by the catastrophic effects (Imax=IX-X MCS) of an earthquake, that probably occurred offshore, in the Salento Plateau (Ionian Sea). Subsequent damage had a complex pattern, whereby some towns were almost razed to the ground and others, nearby, suffered only slight damage. By means of an integrated geological, geotechnical and geophysical analysis we tried to cast a light on the causes of this peculiar distribution of seismic shaking, which we finally modelled by means of a one-dimensional simulation. These results, together with the re-analysis of the macroseismic distribution of the earthquake, and the seismotectonic knowledge of the region, suggest that the 1743 event was a strong, deep one that occurred far from Salento. The event induced high amplification, mainly in the villages (i.e., Nardo and Francavi...
A Critical Revision of the Salento Peninsula Seismicity: The Case of
Introduction. The area of the Salento peninsula (Apulia, Southern Italy) is considered the stable foreland of the Southern Apennines chain (Cinque et al., 1993), although it has been hit by several low energy and a few high energy earthquakes over the last centuries. The aim of this study is a critical revision of the historical and recent seismicity of the Salento peninsula and surrounding seismogenetic areas, for re-evaluating the macroseismic effects in MCS scale and ground effects in natural environment, according to the ESI 2007 scale (Michetti et al., 2007; Guerrieri et al., 2012). In particular, the February 20, 1743 earthquake, the strongest of the area, was reviewed and new MCS intensity values were attributed to some localities. Moreover we have evaluated the most important effects on land in the Salento area due to the strong earthquakes of Northern Apulia, Southern Apennines, Adriatic and Ionian sea, Albania and Greece. The use of both traditional MCS macroseismic intensity scale and the ESI 2007 scale gives a more accurate image of the earthquake (Dengler and McPherson, 1993; Porfido et al., 2007; Serva et al., 2007) and allowed us to better constrain the seismic hazard assessment in the Salento peninsula. Geodynamic background. The central area of the Mediterranean basin is a plate-boundary region of high seismicity and complex tectonics, dominated by frequent earthquake activity occurring mostly in the Ionian Sea and Western Greece. The Apulia region, NW-SE elongated, represents the emerged part of the Adriatic foreland domain shared by the Apennine chain to the west, and the Dinaride-Hellenide chain to the east (Moretti and Royden, 1988). The geodynamic background of this area is characterized by the ongoing subduction of the Ionian slab beneath the Calabrian Arc (Caputo et al., 1970), such compressional regime is still active and outlined by relevant seismicity (Castello et al., 2006). As regards the tectonic setting of the Apennine-Dinaride converging region and surroundings, according to Gambini and Tozzi (1996) the major structural lineaments to be considered are: the Scutari-Pec Line; the Pescara-Dubrovnik dextral shear Line; the North Gargano Fault Zone; the Mattinata Gondola Fault Zone; the South Salento-North Kerkira Fault Zone; the right-lateral Cephalonia Transform Fault (see map in Gambini and Tozzi, 1996). The rigid Apulian foreland block has been deformed through several normal faults, NW-SE and NNW-SSE trending, some of them presently active since they dislocate the sea floor by about 200-300 m (Merlini et al., 2000); moreover, major E-W strike-slip and oblique-slip fault zones divide Apulia into structural blocks behaving independently, among them the Gargano Promontory, the Murge Ridge and the Salento Peninsula are relevant. In particular, the Salento peninsula represents the southernmost part of the Apulia foreland. The outcropping rocks are prevalently limestone-dolomite units belonging to the Apulia platform, with carbonatic-terrigenous marine deposits at the top of the stratigraphic sequence, Middle Eocene-Upper Pleistocene age (Mastronuzzi et al., 2011). The Salento peninsula has undergone a general uplift since Middle Pleistocene, with total amount of about 150 meters; after this period and in more recent times, neotectonic data indicate a significant stability of this area.
Seismic hazard estimates for the Vittorio Veneto broader area (NE Italy)
The logic tree approach has been used to compute robust seismic hazard estimates for NE Italy (Friuli -Venezia Giulia and eastern Veneto regions). These hazard estimates were planned to be used for the expected damage assessment at a regional scale. The logic tree approach has been followed, to quantify the epistemic uncertainties. Our logic tree consists of 54 branches for rock and soft soil conditions for which three seismogenic zonations, representing various levels of seismotectonic knowledge, three methods for seismicity rate computation, three approaches for maximum magnitude estimation, and two PGA attenuation relations of different spatial relevance (Italian, European) were used. For stiff soil conditions, an additional attenuation relation of regional applicability was considered with an enlargement of the logic tree to 81 branches. The regional hazard assessment was made according to a standard probabilistic approach for several return periods: 189 runs were processed in total. The hazard estimates coming from all branches, contribute to the final aggregate seismic hazard map. Two areas (central Friuli and the area around Vittorio Veneto) show the highest hazard in these maps. All results were stored and elaborated by a GIS system, that allowed us to produce the final soil seismic hazard map. The computed PGA with a return period of 475 years in Vittorio Veneto (stiff soil conditions) is 0.38 g, considering the aleatory variability; it becomes 0.51 g when the epistemic uncertainties are added. For damage assessment purposes, an additional hazard map in terms of macroseismic intensity has been obtained transforming the PGA estimates into macroseismic intensity by a relation calibrated on the data of the 1976 Friuli earthquake. The intensity hazard map shows similar features as those of the hazard map in terms of PGA with the maximum values along the northern Tagliamento River valley. Slejko et al. et al., 1995). shows the main seismotectonic features for NE Italy. The tectonic structures are taken from for the Friuli and Slovenia regions (east of 13°) and from for the western sector. The main historical (pre-1977) seismicity (events with M S 4.0 or larger) are taken from the Camassi and Stucchi (1997) catalogue and the recent earthquakes (events with local magnitude M L 3.0 or larger) refer to the hypocentral locations of the Friuli -Venezia Giulia seismometric network (
Seismic hazard assessment in terms of macroseismic intensity for the Italian area a cura di
2010
A seismic hazard map, in terms of macro seismic intensity with 10% probability of exceedance in 50 years, is proposed for the Italian territory. The input elements used to evaluate the seismic hazard are: the seismogenic zoning ZS9 (Meletti et al., 2007), the earthquake catalogue CPTI04 (Gruppo di lavoro CPTI04, 2004) and intensity attenuation relationships. The first two elements and the historical and statistical completeness of the catalogue are those used in the national seismic hazard map for Italy MPS04 (Gruppo di Lavoro MPS, 2004). Two intensity attenuation models are used: 1) one national relationship obtained with a new approach by Pasolini et al. (2006) and a relationship for the Etna volcanic zone proposed by Azzaro et al. (2006) 2) a set of regional relationships derived from a previous cubic model (Berardi et al., 1993) which is recalibrated in the present study using the macro seismic intensity database DBMI04 (Stucchi et al., 2007), which was used for compiling CPTI04...