We present a study to discriminate the kind of anomalous waves, storms or tsunamis, that were res... more We present a study to discriminate the kind of anomalous waves, storms or tsunamis, that were responsible for the large boulder accumulation in the Vendicari Reserve along the south-eastern Sicilian coast. These depositional and erosional indicators of the large wave impact have been already observed in some rocky coasts of the Mediterranean basin and associated to strong waves of tsunamigenic or meteorological origin. Distinguishing boulders deposited by tsunamis from that deposited by storms and determining the age of their deposition can help to evaluate the magnitude and frequency of tsunamis and the hazard along the coast also regarding extraordinarily violent storms. The Sicilian Ionian coast has been affected in historical time by large destructive earthquake-related tsunamis (e.g. the 1169, 1693 and 1908) and it is exposed to an intense wave motion coming from a NNE- SSE span direction . In the rocky coastal area of Vendicari Reserve, three different GPS surveys (from September 2006 until April 2009) have been performed with the aim to observe the distance of each boulders with respect to the shoreline and if storms removed boulders or deposited new ones. A morphological analysis aiming to identify boulder shapes, measuring their volumes, elongation axis azimuth, pre-transport setting and the probable transport mechanism on the platform, was also carried out. The calcarenitic boulders (specific weight about 2,3 g/cm3), reaching about 20 tons and a distance up to 60m from the shoreline, are generally carved out from the supratidal or mid-sublittoral zone, showing widespread biogenic encrustations sometimes so fresh that suggest a recent deposition. The GPS surveys allowed us to observed that, after a strong storm during January 2009, several boulders were removed while new have been deposited on the platform by the storm waves. Hydrodynamic equations jointly to statistical analysis of sea storms have been used to determine the extreme event, geological or meteorological, responsible for this singular accumulation. We computed the minimum wave height, of storm and tsunami, required to start the movement of each boulder from its initial position. Moreover, we calculated the maximum penetration of the waves for the two major storm waves estimated at Vendicari and for the 1693 and 1908 tsunami waves. Finally we compared the computed values with the boulder distribution. The results show that the strongest storms were probably responsible for the current distribution of many boulders but about the 30% of them need of stronger waves, likely tsunami waves, than the maximum assumed storms to be moved and transported in their final place. Radiocarbon dating, performed on three probably tsunami boulders, having weight of about 15 t and sited at a distance >40 m from the shoreline, suggests that two of them were probably deposited by the 1693 tsunami, and one by a tsunami occurred after 650-930 AD that could be an unknown event or one of the historical tsunamis occurred in the Ionian coast of Sicily. Absolute age dating, such as optical stimulated luminescence, should be necessary to gather a correct imprint of the paleotsunami event.
Strong earthquakes can produce direct and permanent geological effects on the earth surface. Beyo... more Strong earthquakes can produce direct and permanent geological effects on the earth surface. Beyond surface faulting, other effects, such as landslides, liquefactions and ground deformations (seismites), take place in the epicentral area as a consequence of the seismic wave propagation in the sediments. Since the last three decades only, these features have been considered indicators of seismicity and their analysis (paleoseismological off-fault study) has been used as an useful tool for obtaining crucial information on the causative earthquake parameters. Such analyses are especially useful in areas where earthquakes occurred before the seismic instrument development or without clear evidence of surface faulting. Since paleoseismology is a youth discipline, the integration of innovative and multidisciplinary techniques and the updating of the case studies on seismites is of fundamental importance. During historical time south-eastern Sicily has been hit by strong earthquakes (M up to 7), such as the 1169, 1542 and 1693 events. Given the lack of surface faulting evidence, the real source location of these earthquakes is a still open question and represents the main gap of the Sicilian seismogenic framework, therefore paleosismological off-fault study can contribute to identify seismogenic sources. Along the NNE-SSW trending rocky coast of Vendicari, we detected a singular association of deformational structures affecting terrains up to Quaternary age. These structures are both soft sediment deformations (autoclastic breccias, diapyr-like injections, dikes and thyxotropic wedges), probably linked to liquefaction mechanisms, and fragile deformations, consisting of opened fractures generally filled by sediment (Neptunian dykes). With the aim to define the deformation mechanisms that affected the deposits at Vendicari, we studied in detail the local stratigraphic sequence and the deformational structures, performing a mesostructural study of the fractures and the analysis of the microscopic characteristic of the filling materials, as well. The systematic and paleostress analyses of the fractures highlighted a high variability in the architectural style and a high dispersion of the plane direction. This is probably linked to more than one deformative mechanism concurring in their development and masking the stress field. A coseismic brittle deformation, linked to the shaking and to the seismic wave propagation, and a lateral spreading and settlement mechanism with fissuring parallel to the coastline (driven by gravity under a moderate topographic gradients), are proposed as probable causes of the fracture development together with the tectonic stress field. However, the analysis of the fractures, filtered and cleaned up from the contribute of the disturb mechanisms, shows a stress field characterized by a probable NW-SE-trending σ1,which iscompatible with the active regional stress. The occurrence of violent coseismic deformation should be also testified by the development of the liquefaction-driven soft sediment deformations, observed in the area, that reveals the application of an horizontal shear stress and of a sudden high hydraulic pressure. The overall analysis of seismites at Vendicari highlights the occurrence of at least three triggering events, occurred after the Pleistocene age. They could be tentatively associate with the historical 1169, 1542 and 1693 earthquakes (I0 ≥X) or with similar or strongest paleoevents, considering the minimum epicentral distances and the minimum intensity at a site (Is ≥ IX) for which an earthquake is capable to induce these association of seismites. The paleoseismological study at Vendicari allowed us to upgrade the paleoseimological off-fault techniques and to increase the study cases in Sicily. Moreover, this study provides, if integrated with similar studies at regional scale, new and useful information on ancient earthquakes in a high-seismicity area like eastern Sicily, for a better characterization of the seismogenic sources.
A singular association of deformation structures that have disturbed terrains up to Quaternary ag... more A singular association of deformation structures that have disturbed terrains up to Quaternary age, has been detected along the rocky coast of Vendicari (south-eastern Sicily). These structures are soft sediment deformations consisting of autoclastic breccias, diapyr-like injections and thixotropic wedges, as well as fractures, generally opened and filled by sediments. Both soft and brittle deformations can be due either to trigger mechanisms internal to the sedimentary environment or to external causes. In order to define the deformation mechanisms affecting the deposits, the local paleo-environmental reconstruction and detailed deformation structure investigations have been performed. Moreover, fractures have been analysed by a mesostructural study and the examination of the microscopic features of the filling materials, to highlight possible relationships with the stress field induced by regional tectonics. The multi-theme analysis allowed us to discard internal trigger mechanisms as responsible of the deformations and to reasonably infer these deformation structures as being seismically induced. This interpretation is also supported by similarities with structures studied in other areas worldwide and commonly interpreted as seismites. The link between these records of seismic activity and the eastern Sicily seismicity is set into evidence by the analysis of the historical accounts which report the occurrence of structures similar to those detected at Vendicari, in several sites close to the study area. A major result of the present study is to improve the catalogue of deformation features, recorded in sedimentary units, attributed to earthquakes.► A case study of both brittle and soft-sedimentary deformations was performed. ► Analyses allowed to discard internal causes as responsible of the deformations. ► Investigations showed that the deformation structures are seismically induced. ► Seismites are triggered by earthquakes with M greater than 5 and I greater than IX.
Five years ago we started a coring campaign with the purpose to identify evidence for tsunami inu... more Five years ago we started a coring campaign with the purpose to identify evidence for tsunami inundations along the coastal areas of eastern Sicily, that were affected in historical times by devastating tsunamis, generated both by local earthquakes, such as the 1169, 1693 and 1908 events, and by distant seismic sources, such as those belonging to the Aegean subduction zone (e.g. the A.D. 365 Crete earthquake). Following a multi-theme approach, we used the available historical information to address geomorphological study of the coastal landscape: aerial-photographs analysis, satellite images interpretation and field surveys allowed us to select areas likely invaded by tsunami waves in the past, representing potential trap-site for high energy deposits sedimentation and preservation. Given the variability in the nature of tsunami deposit characteristics, they are not uniquely identifiable, and other kinds of high energy deposits may share some of their features. Despite the abundant literature regarding diagnostic criteria for tsunami deposits, their distinction from storm and hurricane deposits remains a debated issue. We present the geological evidence of a tsunami inundation that left continuous onshore sandy deposit inside the Pantano Morghella along the south-eastern Sicilian coast. Pantano Morghella an almost flat area, about 1.3 km long and 0.8 km wide, surrounded by Upper Cretaceous lavas and volcanoclastic deposits, Late Cretaceous limestone calciruditi, calcarenites and marls. To the east Quaternary deposits, beach sands and 3 m high, partially cemented, dunal system (Holocene and Late Pleistocene) separate the Pantano from the sea forming the intertidal pond with a little channel from which sea water can rush into. The site was partially used as salt-pans in the recent past. In this site, we dug 33 cores down to a maximum depth of 5.80 m, from 200 m up to 1200 m from the coastline. The sedimentological core analysis reveals a fine stratigraphic sequence mainly composed by clay and silty clay, interrupt by a yellow sandy layer (about 8-10 cm thick) at about one meter of depth. Paleontological analyses show that the sandy samples have different macro and microfauna composition with respect to those samples collected above and below characterized by a lagoonal assemblage. The sandy layer, mainly composed by well-rounded yellowish carbonatic clasts, is made of several reworked foraminifera (both planktonic and benthonic), few well preserved littoral benthic foraminifera, marine macro fossil fragments and few lagoonal specimens. The deposit shows similarity with the local beach sand and it also presents a landward thinning. X-Ray analysis performed on some selected cores shows that the sandy layer is characterized by a fining upward granulometry and a sharp basal contact, possibly erosional. Summarizing, we investigated spatial distribution and lithofacies of this peculiar deposit and observed the following properties as typical of high energy deposition event: (1) the deposit covers the surface almost continuously on gentle topography and extend inland for about 1200 meters; (2) its thickness varies across local surface undulation; (3) the foraminiferal assemblage contains several reworked marine planktonic and benthonic specimens with some lagoonal species; (4) the deposit is characterized by erosive basal contact. Moreover, its composition consisting of a single structureless bed of normally graded sand, its thickness decreasing with distance from the sea and its landward limit represent attributes that strongly suggest a tsunami origin. Radiocarbon dating, performed on three samples collected just above, within and below the sandy anomalous layer, gives ages close in time, confirming a sudden deposition due to a high energy event occurred in the interval 270-650 A.D. Comparing this age with the historical tsunami catalogue, we can hypothesize that the sandy layer represents the geological record of the 365 A.D. Crete tsunami.
ABSTRACT A new dataset of landslides, occurred in a tectonically active region, has been analysed... more ABSTRACT A new dataset of landslides, occurred in a tectonically active region, has been analysed in order to understand the causes of the slope instability. The landslides we have dealt with took place along the volcanic rock cliff of S. Caterina and S. Maria La Scala villages (eastern Sicily, Italy), a densely inhabited area located on the eastern margin of Mt. Etna, where some seismogenic faults, locally named Timpe system, slip during moderate local earthquakes and also move with aseismic creep mechanisms. The results show that landslides are triggered by heavy rainfalls, earthquakes and creep fault episodes. Indeed, they occur along discrete fault segments, exhibiting a combination of both brittle failure, indicated by the earthquake occurrence, and aseismic creep events. The analysis of seismicity occurred on the Timpe fault system has shown that the active Acireale fault, in its southernmost segment, is subject to an aseismic sliding, which increases after the stick–slip motion in the nearby faults. Therefore, aseismic creep seems to concur in the predisposition of a rock to fail, since strains can increase the jointing of rock masses leading to a modification in the slope stability. Understanding the factors concurring to the slope instability is a useful tool for future assessments of the landslide hazard in densely settled areas, located on a volcanic edifice, such as Etna that is slowly sliding seawards, and where active faults, seismicity and heavy rains affect the deeply fractured slopes.
We present a study to discriminate the kind of anomalous waves, storms or tsunamis, that were res... more We present a study to discriminate the kind of anomalous waves, storms or tsunamis, that were responsible for the large boulder accumulation in the Vendicari Reserve along the south-eastern Sicilian coast. These depositional and erosional indicators of the large wave impact have been already observed in some rocky coasts of the Mediterranean basin and associated to strong waves of tsunamigenic or meteorological origin. Distinguishing boulders deposited by tsunamis from that deposited by storms and determining the age of their deposition can help to evaluate the magnitude and frequency of tsunamis and the hazard along the coast also regarding extraordinarily violent storms. The Sicilian Ionian coast has been affected in historical time by large destructive earthquake-related tsunamis (e.g. the 1169, 1693 and 1908) and it is exposed to an intense wave motion coming from a NNE- SSE span direction . In the rocky coastal area of Vendicari Reserve, three different GPS surveys (from September 2006 until April 2009) have been performed with the aim to observe the distance of each boulders with respect to the shoreline and if storms removed boulders or deposited new ones. A morphological analysis aiming to identify boulder shapes, measuring their volumes, elongation axis azimuth, pre-transport setting and the probable transport mechanism on the platform, was also carried out. The calcarenitic boulders (specific weight about 2,3 g/cm3), reaching about 20 tons and a distance up to 60m from the shoreline, are generally carved out from the supratidal or mid-sublittoral zone, showing widespread biogenic encrustations sometimes so fresh that suggest a recent deposition. The GPS surveys allowed us to observed that, after a strong storm during January 2009, several boulders were removed while new have been deposited on the platform by the storm waves. Hydrodynamic equations jointly to statistical analysis of sea storms have been used to determine the extreme event, geological or meteorological, responsible for this singular accumulation. We computed the minimum wave height, of storm and tsunami, required to start the movement of each boulder from its initial position. Moreover, we calculated the maximum penetration of the waves for the two major storm waves estimated at Vendicari and for the 1693 and 1908 tsunami waves. Finally we compared the computed values with the boulder distribution. The results show that the strongest storms were probably responsible for the current distribution of many boulders but about the 30% of them need of stronger waves, likely tsunami waves, than the maximum assumed storms to be moved and transported in their final place. Radiocarbon dating, performed on three probably tsunami boulders, having weight of about 15 t and sited at a distance >40 m from the shoreline, suggests that two of them were probably deposited by the 1693 tsunami, and one by a tsunami occurred after 650-930 AD that could be an unknown event or one of the historical tsunamis occurred in the Ionian coast of Sicily. Absolute age dating, such as optical stimulated luminescence, should be necessary to gather a correct imprint of the paleotsunami event.
Strong earthquakes can produce direct and permanent geological effects on the earth surface. Beyo... more Strong earthquakes can produce direct and permanent geological effects on the earth surface. Beyond surface faulting, other effects, such as landslides, liquefactions and ground deformations (seismites), take place in the epicentral area as a consequence of the seismic wave propagation in the sediments. Since the last three decades only, these features have been considered indicators of seismicity and their analysis (paleoseismological off-fault study) has been used as an useful tool for obtaining crucial information on the causative earthquake parameters. Such analyses are especially useful in areas where earthquakes occurred before the seismic instrument development or without clear evidence of surface faulting. Since paleoseismology is a youth discipline, the integration of innovative and multidisciplinary techniques and the updating of the case studies on seismites is of fundamental importance. During historical time south-eastern Sicily has been hit by strong earthquakes (M up to 7), such as the 1169, 1542 and 1693 events. Given the lack of surface faulting evidence, the real source location of these earthquakes is a still open question and represents the main gap of the Sicilian seismogenic framework, therefore paleosismological off-fault study can contribute to identify seismogenic sources. Along the NNE-SSW trending rocky coast of Vendicari, we detected a singular association of deformational structures affecting terrains up to Quaternary age. These structures are both soft sediment deformations (autoclastic breccias, diapyr-like injections, dikes and thyxotropic wedges), probably linked to liquefaction mechanisms, and fragile deformations, consisting of opened fractures generally filled by sediment (Neptunian dykes). With the aim to define the deformation mechanisms that affected the deposits at Vendicari, we studied in detail the local stratigraphic sequence and the deformational structures, performing a mesostructural study of the fractures and the analysis of the microscopic characteristic of the filling materials, as well. The systematic and paleostress analyses of the fractures highlighted a high variability in the architectural style and a high dispersion of the plane direction. This is probably linked to more than one deformative mechanism concurring in their development and masking the stress field. A coseismic brittle deformation, linked to the shaking and to the seismic wave propagation, and a lateral spreading and settlement mechanism with fissuring parallel to the coastline (driven by gravity under a moderate topographic gradients), are proposed as probable causes of the fracture development together with the tectonic stress field. However, the analysis of the fractures, filtered and cleaned up from the contribute of the disturb mechanisms, shows a stress field characterized by a probable NW-SE-trending σ1,which iscompatible with the active regional stress. The occurrence of violent coseismic deformation should be also testified by the development of the liquefaction-driven soft sediment deformations, observed in the area, that reveals the application of an horizontal shear stress and of a sudden high hydraulic pressure. The overall analysis of seismites at Vendicari highlights the occurrence of at least three triggering events, occurred after the Pleistocene age. They could be tentatively associate with the historical 1169, 1542 and 1693 earthquakes (I0 ≥X) or with similar or strongest paleoevents, considering the minimum epicentral distances and the minimum intensity at a site (Is ≥ IX) for which an earthquake is capable to induce these association of seismites. The paleoseismological study at Vendicari allowed us to upgrade the paleoseimological off-fault techniques and to increase the study cases in Sicily. Moreover, this study provides, if integrated with similar studies at regional scale, new and useful information on ancient earthquakes in a high-seismicity area like eastern Sicily, for a better characterization of the seismogenic sources.
A singular association of deformation structures that have disturbed terrains up to Quaternary ag... more A singular association of deformation structures that have disturbed terrains up to Quaternary age, has been detected along the rocky coast of Vendicari (south-eastern Sicily). These structures are soft sediment deformations consisting of autoclastic breccias, diapyr-like injections and thixotropic wedges, as well as fractures, generally opened and filled by sediments. Both soft and brittle deformations can be due either to trigger mechanisms internal to the sedimentary environment or to external causes. In order to define the deformation mechanisms affecting the deposits, the local paleo-environmental reconstruction and detailed deformation structure investigations have been performed. Moreover, fractures have been analysed by a mesostructural study and the examination of the microscopic features of the filling materials, to highlight possible relationships with the stress field induced by regional tectonics. The multi-theme analysis allowed us to discard internal trigger mechanisms as responsible of the deformations and to reasonably infer these deformation structures as being seismically induced. This interpretation is also supported by similarities with structures studied in other areas worldwide and commonly interpreted as seismites. The link between these records of seismic activity and the eastern Sicily seismicity is set into evidence by the analysis of the historical accounts which report the occurrence of structures similar to those detected at Vendicari, in several sites close to the study area. A major result of the present study is to improve the catalogue of deformation features, recorded in sedimentary units, attributed to earthquakes.► A case study of both brittle and soft-sedimentary deformations was performed. ► Analyses allowed to discard internal causes as responsible of the deformations. ► Investigations showed that the deformation structures are seismically induced. ► Seismites are triggered by earthquakes with M greater than 5 and I greater than IX.
Five years ago we started a coring campaign with the purpose to identify evidence for tsunami inu... more Five years ago we started a coring campaign with the purpose to identify evidence for tsunami inundations along the coastal areas of eastern Sicily, that were affected in historical times by devastating tsunamis, generated both by local earthquakes, such as the 1169, 1693 and 1908 events, and by distant seismic sources, such as those belonging to the Aegean subduction zone (e.g. the A.D. 365 Crete earthquake). Following a multi-theme approach, we used the available historical information to address geomorphological study of the coastal landscape: aerial-photographs analysis, satellite images interpretation and field surveys allowed us to select areas likely invaded by tsunami waves in the past, representing potential trap-site for high energy deposits sedimentation and preservation. Given the variability in the nature of tsunami deposit characteristics, they are not uniquely identifiable, and other kinds of high energy deposits may share some of their features. Despite the abundant literature regarding diagnostic criteria for tsunami deposits, their distinction from storm and hurricane deposits remains a debated issue. We present the geological evidence of a tsunami inundation that left continuous onshore sandy deposit inside the Pantano Morghella along the south-eastern Sicilian coast. Pantano Morghella an almost flat area, about 1.3 km long and 0.8 km wide, surrounded by Upper Cretaceous lavas and volcanoclastic deposits, Late Cretaceous limestone calciruditi, calcarenites and marls. To the east Quaternary deposits, beach sands and 3 m high, partially cemented, dunal system (Holocene and Late Pleistocene) separate the Pantano from the sea forming the intertidal pond with a little channel from which sea water can rush into. The site was partially used as salt-pans in the recent past. In this site, we dug 33 cores down to a maximum depth of 5.80 m, from 200 m up to 1200 m from the coastline. The sedimentological core analysis reveals a fine stratigraphic sequence mainly composed by clay and silty clay, interrupt by a yellow sandy layer (about 8-10 cm thick) at about one meter of depth. Paleontological analyses show that the sandy samples have different macro and microfauna composition with respect to those samples collected above and below characterized by a lagoonal assemblage. The sandy layer, mainly composed by well-rounded yellowish carbonatic clasts, is made of several reworked foraminifera (both planktonic and benthonic), few well preserved littoral benthic foraminifera, marine macro fossil fragments and few lagoonal specimens. The deposit shows similarity with the local beach sand and it also presents a landward thinning. X-Ray analysis performed on some selected cores shows that the sandy layer is characterized by a fining upward granulometry and a sharp basal contact, possibly erosional. Summarizing, we investigated spatial distribution and lithofacies of this peculiar deposit and observed the following properties as typical of high energy deposition event: (1) the deposit covers the surface almost continuously on gentle topography and extend inland for about 1200 meters; (2) its thickness varies across local surface undulation; (3) the foraminiferal assemblage contains several reworked marine planktonic and benthonic specimens with some lagoonal species; (4) the deposit is characterized by erosive basal contact. Moreover, its composition consisting of a single structureless bed of normally graded sand, its thickness decreasing with distance from the sea and its landward limit represent attributes that strongly suggest a tsunami origin. Radiocarbon dating, performed on three samples collected just above, within and below the sandy anomalous layer, gives ages close in time, confirming a sudden deposition due to a high energy event occurred in the interval 270-650 A.D. Comparing this age with the historical tsunami catalogue, we can hypothesize that the sandy layer represents the geological record of the 365 A.D. Crete tsunami.
ABSTRACT A new dataset of landslides, occurred in a tectonically active region, has been analysed... more ABSTRACT A new dataset of landslides, occurred in a tectonically active region, has been analysed in order to understand the causes of the slope instability. The landslides we have dealt with took place along the volcanic rock cliff of S. Caterina and S. Maria La Scala villages (eastern Sicily, Italy), a densely inhabited area located on the eastern margin of Mt. Etna, where some seismogenic faults, locally named Timpe system, slip during moderate local earthquakes and also move with aseismic creep mechanisms. The results show that landslides are triggered by heavy rainfalls, earthquakes and creep fault episodes. Indeed, they occur along discrete fault segments, exhibiting a combination of both brittle failure, indicated by the earthquake occurrence, and aseismic creep events. The analysis of seismicity occurred on the Timpe fault system has shown that the active Acireale fault, in its southernmost segment, is subject to an aseismic sliding, which increases after the stick–slip motion in the nearby faults. Therefore, aseismic creep seems to concur in the predisposition of a rock to fail, since strains can increase the jointing of rock masses leading to a modification in the slope stability. Understanding the factors concurring to the slope instability is a useful tool for future assessments of the landslide hazard in densely settled areas, located on a volcanic edifice, such as Etna that is slowly sliding seawards, and where active faults, seismicity and heavy rains affect the deeply fractured slopes.
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