134574203
Active Tectonics along the South East Offshore Margin of Mt. Etna: New Insights from High-Resolution Seismic Profiles
The offshore margin of Mt. Etna has been shaped by Middle Pleistocene to Holocene shortening and extension and, more recently, by gravity-related sliding of the volcanic edifice. These processes have acted contemporaneously although the gravitational component largely prevails over the tectonic one. In order to investigate this issue, we focused on the main role of active tectonics along the south-eastern offshore of Mt. Etna by means of marine high-resolution seismic data. Seismic profiles revealed post-220 ka sedimentary deposits unconformably overlaying the Lower-Middle Pleistocene Etnean clayey substratum and volcanics of the Basal Tholeiitic phase and the Timpe phase. Offshore Aci Trezza-Catania, the architecture of the sedimentary deposits reflects syn-tectonic deposition occurred into “piggy-back” basin setting. Shortening rate was estimated at ~0.5 mm/a since ~220 ka. Asymmetric folding also involves post Last Glacial Maximum deposits, evidencing that compressional deformation is still active. In the continental slope, a belt of normal faults offset the Lower-Middle Pleistocene Etnean clayey substratum and younger deposits, also producing seafloor ruptures. Thrust and fold structures can be related to the recent migration of the Sicilian chain front, while extensional faults are interpreted as part of a major tectonic boundary located in the Ionian offshore of Sicily.
129866218
GPS velocity and strain fields in Sicily and southern Calabria, Italy: updated geodetic constraints on tectonic block interaction in the central Mediterranean
[1] We present an improved rendition of the geodetic velocity and strain fields in Sicily and southern Calabria obtained through the analysis of 18 years of GPS observations from continuous and survey station networks. The dense spatial coverage of geodetic data provides precise quantitative estimates of previously established first-order active kinematic features, including: i) a narrow east-west-elongated belt of contraction (∼1–1.5 mm/yr) extending offshore northern Sicily from Ustica to Stromboli across the Aeolian Islands; ii) a narrow east-west-trending contractional belt located along the northern rim of the Hyblean Plateau in southern Sicily, with shortening at up to 4.4 mm/yr; iii) right motion (∼3.6 mm/yr) on the Aeolian-Tindari-Letojanni fault (ATLF) system, a main shear zone extending from the Aeolian Islands to the Ionian coast of Sicily, with significant transpression and transtension partitioned between discrete sectors of the fault; iv) transtension (∼1 mm/yr) across the Sicily Channel between Sicily and North Africa. We use geodetic observations coupled to geological constraints to better elucidate the interplay of crustal blocks revealed in the investigated area. In particular, we focus on the ATLF, which forms the primary boundary between the Sicilian and Calabrian blocks. The ATLF juxtaposes north-south contraction between Sicily and the Tyrrhenian block with northwest-southeast extension in northeastern Sicily and Calabria. Contraction between Sicily and Tyrrhenian blocks probably arises from the main Europe-Nubia convergence, although Sicily has a component of lateral motion away from Nubia. We found that convergence is not restricted to the northern offshore, as commonly believed, but is widely accommodated between the frontal belt and the northern rim of the Hyblean foreland in southern Sicily. Geodetic data also indicate that active right shear on the ATLF occurs to the southeast of the mapped fault array in northern Sicily, suggesting the fault cuts through till the Ionian coast of the island. The small geodetic divergence between the Hyblean and Apulian blocks rimming on both sides the Calabria block and subjacent Ionian slab, coupled with marine geophysical evidences in the Ionian Sea lends credit to the proposed deep root of the ATLF and to a fragmentation of the Ionian domain.
129121316
Geometry and kinematics of the fault systems controlling the unstable flank of Etna volcano (Sicily)
Abstract An updated tectonic framework of Etna's unstable flank has been defined as a result of multidisciplinary analyses carried out by integrating geological and geophysical data. The different typologies of datasets have been analyzed and correlated in order to constrain the geometry and kinematics of the fault systems controlling the unstable flank of Etna volcano and to better understand their complex relationship with the offshore morphostructures of the continental margin. In particular, we have considered as the main structural elements the following four fault systems: Pernicana, Ragalna, Tremestieri–Trecastagni and Timpe. Slip-rates and kinematics have been estimated in both long- and short-terms, respectively, from geological and seismotectonic/geodetic data. Data integration has allowed defining five kinematic domains in the sliding flank of Etna: (1) the NE block, bordered by the Pernicana fault and characterised by the highest deformation velocities; ground velocity progressively diminishes toward South, with a clockwise rotation of the vectors defining (2) the block embracing the central part of the Timpe system; (3) the Giarre wedge; (4) the Medium-East block, bounded by the S. Tecla and Trecastagni faults; and (5) the SE block bordered, by the hidden Belpasso-Ognina tectonic lineament. The dynamics of these blocks takes place through discontinuous movements: sudden short-term accelerations related to the magma intrusion are superimposed to a fairly constant mid-term ESE sliding. The proposed comprehensive model of the unstable flank provides the basic input parameters for applying analytical models to flank dynamics of Etna volcano.
129623172
Dynamics of Mount Etna Volcano inferred from static and kinematic GPS measurements
[1] Ground deformations measured on Mount Etna from late 1995 to mid-1998 using GPS observations are analyzed. Four GPS surveys were carried out during the considered period. In 1995 the GPS network consisted of 18 stations on the volcanic edifice and 6 stations around it. During the 1996 survey, 22 new monuments were added along a N-S profile crossing the summit craters area. This profile was surveyed by a semikinematic method, allowing greater spatial detail to be achieved on the uppermost part of the volcano. The comparisons between the GPS surveys are reported here in terms of horizontal and vertical displacements for each station and also in terms of areal dilatation and strain distribution. This last parameter continues its ascending trend, at a rate of ∼5 μstrain yr−1, already shown in the previous period, after the end of the 1991–1993 flank eruption. Inversion of the ground deformation patterns permits investigation of the evolution of both the position and dynamics of magma reservoirs beneath the volcano, consistently associated with a general eastward sliding of its eastern sector. This study allows us to define the nonuniqueness of ground deformation sources through the investigated period, suggesting that the plumbing system of the volcano is made up of a complex system of single intrusions occurring at different times.
128413703
Dynamics of the eastern flank of Mt. Etna volcano (Italy) investigated by a dense GPS network
Abstract Mount Etna has developed at the intersection of two regional tectonic lineaments, the NNW–SSE trending Hybleo–Maltese escarpment, which separates the thick inland continental crust of the African platform from the Ionian Mesozoic oceanic crust, and the NE–SW Messina–Fiumefreddo fault that marks a rift zone between south Calabria and north-eastern Sicily, extending as far as the Mt. Etna area. All tectonic features affect, with outstanding surface features, the eastern side of the volcano. The eastern flank of the volcano is affected by a long-term motion toward ESE. In 1997, in order to increase the detail of the ground deformation pattern on the lower eastern flank of Mt. Etna, a new GPS network, the “Ionica” network, was installed on this sector of the volcano. This GPS network consists of 24 stations and covers the lower eastern flank of the volcano from the town of Catania to Taormina and from the coastline up to an altitude of about 1300 m. All the new stations consist in self-centring benchmarks; this kind of benchmark allows all station set-up errors to be avoided. Before the merging of the Ionica network to the frame of the global GPS network of Mt. Etna (in June 2001), three surveys were carried out on this network: in September 1997, August 1998 and January 2001. From the ground deformation pattern, it is possible to distinguish two different sectors, showing different characteristics of deformation. The southern part of the network shows a more uniform distribution of the vertical motion with a mean SE-ward horizontal component while the northern one shows an heterogeneous vertical motion with a ESE-ward horizontal component. Furthermore, a higher velocity is detected between 1997 and 1998, due to the additional stress induced by a shallow intrusion on the NW flank of the volcano. The model resulting from data inversions defines a wide sliding plane beneath the entire eastern flank of the volcano with a low dip angle. The expected velocity vectors fit well the observed ones, even if the measured velocities are still quite higher than expected, at lowermost stations. The vertical inclination of the velocity vectors measured during the 1998–2001 period, gradually decreases from West to East suggesting a sort of rotational movement of the south-eastern flank, interrupted by some anomalous vectors on the lower part, that show higher vertical velocities. These anomalies, being located on a wedge defined by the intersection of the main NNW–SSE and NE–SW fault systems and near the Timpe faults, are probably due to the activity of the vertical faults cutting the lower eastern flank of Mt. Etna. Stations lying on the hanging wall and on the footwall of the Timpe fault system are affected by similar horizontal displacements, meaning that these structures are moving eastwards together with the sliding flank; this evidence suggests that the Timpe faults are probably second order structures, with respect to the detachment surface. These results depict a structural framework of the eastern flank of Mt. Etna in which the low angle dislocation can be considered as a first order approximation of an actual listric plane and the current active part of the Timpe fault system is confined above the detachment surface.
140693886
Active spreading and regional extension at Mount Etna imaged by SAR interferometry
Abstract Large-flank instability has been proposed by most recent authors as a major process in the dynamics of Mount Etna. However, several aspects of the models are still disputed, such as the boundaries of the moving area and the driving force for the instability. In this paper we present synthetic aperture radar interferometric data which allow us to identify two main sectors of active instability where the deformational process differs. An eastern sector is bounded to the north by the Pernicana–Provenzana fault, to the west by the North Rift Zone and the South Rift Zone and to the south by the Mascalucia–Tremestieri–Trecastagni fault system. Interferograms provide new data on the activity and extent of the southern boundary, which was previously underestimated. In this sector the structural features indicate an eastward sliding, driven by E–W regional extension, which can be interpreted as a result of the retreating slab of the Ionian subduction. A second collapsing sector exists along the southern flank of Mount Etna, where the interferograms show the presence of an active anticlinal ridge. This ridge is interpreted as the result of southward gravity spreading over a basal decollement between Etna and its Plio–Quaternary basement and the Hyblean platform. The two sectors first became active in summer 1996, after the beginning of a new cycle of eruptive activity at the summit. The activity was ongoing until January 1998, with the deformation rate ranging from 4–6 mm/yr for the Mascalucia–Tremestieri–Trecastagni faults to 12 mm/yr for the anticlinal ridge.
59440867
Gravity and magma induced spreading of Mount Etna volcano revealed by satellite radar interferometry
[1] Mount Etna underwent a cycle of eruptive activity over the past ten years. Here we compute ground displacement maps and deformation time series from more than 400 radar interferograms to reveal Mount Etna's average and time varying surface deformation from 1992 to 2001. We find that during this time interval it experienced magmatic inflation and radial spreading to the West, South, and East. Steady relative motion between the West and South flanks, and between the East and North flanks, during this time interval, suggests they are related to gravitational spreading of the volcanic edifice. Time series analysis shows that growth of a southeastern basal anticline began with the end of magma recharge in 1995, thus showing a direct link between deep-seated magma intrusions and edifice spreading. These observations support a complex mode of radial gravitational collapse underlain by deeper magma driven basal spreading, although ultimately the two must be related.
128511447
Structural assessment of Mount Etna volcano from Permanent Scatterers analysis
A study of the deformation pattern of Mount Etna volcano based on the results from the Permanent Scatterers (PS) technique is reported. Ground motion data provided by the interferometric synthetic aperture radar (InSAR) PS technique from 1995 to 2000 are compared and validated by GPS data. An analysis of the ascending and descending line of sight (LOS) components of ground velocities has yielded detailed ground deformation maps and cross sections. This analysis allows detection and constraint of discontinuities in the surface velocity field. LOS velocities have then been combined to calculate the vertical and horizontal (E-W) ground velocities. A wide inflation of the edifice has been detected on the western and northern flanks (over an area of about 350 km2). A seaward motion of the eastern and southern flanks has also been measured. PS data allows the geometry and kinematics of the several blocks composing the unstable flanks to be defined even in the highly urbanized areas, and their displacement rates have been measured with millimeter precision. This analysis reveals the extension of some features beyond their field evidences and defines new important features. The results of this work depict a new comprehensive kinematic model of the volcano highlighting the gravitational reorganization of the unbuttressed volcanic pile on its slippery clay basement on the southern flank, but an additional drag force due to a strong subsidence of the continental margin facing the Etna volcano is necessary to explain the PS velocity field observed on the eastern flank.
53325127
Tectonic expression of an active slab‐tear from high‐resolution seismic and bathymetric data offshore Sicily (Ionian Sea)
Subduction of a narrow slab of oceanic lithosphere beneath a tightly curved orogenic arc requires the presence of at least one lithospheric scale tear fault. While the Calabrian subduction beneath southern Italy is considered to be the type example of this geodynamic setting, the geometry, kinematics and surface expression of the associated lateral, slab tear fault offshore eastern Sicily remain controversial. Results from a new marine geophysical survey conducted in the Ionian Sea, using high-resolution bathymetry and seismic profiling reveal active faulting at the seafloor within a 140 km long, two-branched fault system near Alfeo Seamount. The previously unidentified 60 km long NW trending North Alfeo Fault system shows primarily strike-slip kinematics as indicated by the morphology and steep-dipping transpressional and transtensional faults. Available earthquake focal mechanisms indicate dextral strike-slip motion along this fault segment. The 80 km long SSE trending South Alfeo fault system is expressed by one or two steeply dipping normal faults, bounding the western side of a 500+ m thick, 5 km wide, elongate, syntectonic Plio-Quaternary sedimentary basin. Both branches of the fault system are mechanically capable of generating magnitude 6–7 earthquakes like those that struck eastern Sicily in 1169, 1542, and 1693.
130154063
Geological, seismological and geodetic evidence of active thrusting and folding south of Mt. Etna (eastern Sicily): Revaluation of “seismic efficiency” of the Sicilian Basal Thrust
Abstract Geological studies and morphological analysis, compared with seismological and geodetic data, suggest that a compressive regime currently occurs at crustal depth in the western sector of Mt. Etna, accommodated by shallow thrusting and folding at the front of the chain, south of the volcanic edifice. In particular, a large WSW-ENE trending anticline, interpreted as detachment fold, is growing west and north of Catania city (the Catania anticline). Geological data suggest that during the last 6000 years the frontal fold has been characterized by uplift rates of ∼6 mm/yr along the hinge, consistent with the interferometric data (10 mm/yr) recorded in the last 20 years. Moreover, a NNW-SSE oriented axis of compression has been obtained by seismological data, consistent with GPS measurements over the last 20 years which have revealed a shortening rate of ∼5 mm/yr along the same direction. Besides the activity related to the volcanic feeding system, the seismic pattern under the Mt. Etna edifice can be certainly related to the regional tectonics. The compressive stress is converted into elastic accumulation and then in earthquakes along the ramps beneath the chain, whereas on the frontal area it is accommodated by aseismic deformation along an incipient detachment within the clayish foredeep deposits. The high rate of shortening at the aseismic front of the chain, suggests a greater “seismic efficiency” in correspondence of ramps at the rear.
128898375
Continental margin large-scale instability controlling the flank sliding of Etna volcano
Abstract Etna volcano is affected by a downward sliding of its eastern flank, as rapid as a few cm/year, whose nature is highly debated. Recently collected marine geological and geophysical data allows a detailed image of the morphostructural setting of the continental margin facing the volcano. Here, a large bulge offsets the margin that is deeply affected by widespread semicircular steps, interpreted as evidence of large-scale gravitational instability. Such features permeate the whole margin and extend inshore to the volcano sector where the larger ground deformations are measured. Both submarine instability and subaerial flank sliding are bounded by two regional tectonic lineaments interpreted as weakness lines. These cross the coastline to accommodate the basinward movement of this large sector of the continental margin topped by the Etna volcanic pile. The new data allows re-interpreting the tectonic setting of the coastal belt and proposing a novel structural model, highlighting the active role of the continental margin instability to drive the seaward sliding of the volcano's eastern flank. This model may suggest why a very active basaltic volcano has so unusually developed in front of an active thrust belt.
129730559
Earthquake surface faulting at Mount Etna volcano (Sicily) and implications for active tectonics
Recognition of active faults and assessment of their kinematics constrain thedeformative model of an area. Thus, observations on coseismic faulting at Etna can provideeffective evidence on ongoing tectonics and fault activity. The present study has allowed therecognition of surface ruptures for a large number of earthquakes (50) that have occurred since1818 by means of a careful search and re-examination of historical sources and recent data.Analysis of surface faulting has provided a clearer relationship between seismicity and mappedstructures, and also a better definition of the volcanos tectonic framework through theidentification of previously unknown, hidden faults. Critical interpretation of data and ad hoc field investigations also allowed the verification of kinematics, slip per event, length ofrupture, and the geometry of seismogenic segments providing new data for seismic hazardassessment. © 1999 Elsevier Science Ltd. All rights reserved.
140165832
A comprehensive interpretative model of slow slip events on Mt. Etna's eastern flank
Starting off from a review of previous literature on kinematic models of the unstable eastern flank of Mt. Etna, we propose a new model. The model is based on our analysis of a large quantity of multidisciplinary data deriving from an extensive and diverse network of INGV monitoring devices deployed along the slopes of the volcano. Our analysis had a twofold objective: first, investigating the origin of the recently observed slow-slip events on the eastern flank of Mt. Etna; and second, defining a general kinematic model for the instability of this area of the volcano. To this end, we investigated the 2008–2013 period using data collected from different geochemical, geodetic, and seismic networks, integrated with the tectonic and geologic features of the volcano and including the volcanic activity during the observation period. The complex correlations between the large quantities of multidisciplinary data have given us the opportunity to infer, as outlined in this work, that the fluids of volcanic origin and their interrelationship with aquifers, tectonic and morphological features play a dominant role in the large scale instability of the eastern flank of Mt. Etna. Furthermore, we suggest that changes in the strain distribution due to volcanic inflation/deflation cycles are closely connected to changes in shallow depth fluid circulation. Finally, we propose a general framework for both the short and long term modeling of the large flank displacements observed.
129619111
Active thrusting as a possible seismogenic source in Sicily (Southern Italy): Some insights from integrated structural–kinematic and seismological data
Abstract This paper proposes a new seismogenic interpretation of mainland and central-southern Sicily, based on an integrated structural–kinematic–seismological approach. Through analysis of available structural and geophysical data, the tectonic setting, the major kinematic units and the crust geometry of the Sicilian southward-verging fold-and-thrust belt system are schematized in sections and in map form. The depth-contour lines of the outermost basal thrust plane, which dates back to Plio-Pleistocene times with some evidence of Holocene activity, are reconstructed. This plane, here named Sicilian Basal Thrust (SBT), emerges along the southward convex Sciacca–Gela–Catania front and reaches the base of the crust at a depth of about 30 km beneath northern Sicily. Additionally, an important regional upper crust splay, with the same arched shape, has been identified some kilometres northward. In order to detect any possible indication of seismogenic activity linked to ongoing deformation of the SBT and its splay, we analyzed the distribution and kinematics of the instrumental seismicity in the period between 1981 and 2006. Particular attention was given to the background seismicity (Ml up to 4.6) located beneath the sedimentary cover at Mt. Etna, as it allows individuating a northward deepening seismogenic volume undergoing an average N–S compression, which corresponds well with the SBT geometry in section view. A merged dataset of all the known major historical and instrumental events (moment magnitude ≥ 4.5) that occurred above the SBT 0-to-30 km depth-contour lines from 217 B.C. to 2006 was compiled and analyzed. Based on information from instrumental data and/or on speculations on the shape and extent of the historical earthquake macroseismic fields, two major ranges of hypocentral depths have been schematically identified within the merged dataset: an upper crust range (in average
140668881
The Tectonics and Geodynamics of Mt. Etna: Synthesis and Interpretation of Geological and Geophysical Data
The eastern flank of Mt. Etna is traversed by faults of the Aeolian-Maltese system, which has the role of a transform fault in the Calabrian-Sicilian arc and divides it into two parts: toward the east, its Jonian part has the characteristics of an active margin, while in its western part, subduction is blocked and the area shows a collisional regime. The synthesis of the tectonic data on the volcano, its substratum, its periphery, and on this sector of the Apenninic-Maghrebian chain, reveals a complex situation: this is largely due to the proximity of the volcano to the Aeolian-Maltese fault system and also to the evolution of the stress field, in relation to the growth of the Etnean edifice. Today the geophysical data indicate a compressive stress field at depth (10 km), with σ 1 being oriented N-S. At depths of <10 km, below and within the volcano, stress distribution is modified by various factors such as magmatism, burden of the volcanic edifice, and gravity. On a more general scale, at the surface, compression in the chain is continuing. The transforming Aeolian-Maltese fault system delimits two sectors in the volcano: toward the west, the neotectonic and geophysical data indicate that Mt. Etna functions in a compressive context, modified at the surface by the presence of the volcano and its activity, while toward the east the data testify to an extensional stress regime, which controls north-eastern Sicily and a significant portion of Calabria.
130546114
Quaternary normal faulting in southeastern Sicily (Italy): a seismic source for the 1693 large earthquake
SUMMARY We present geological and morphological data, combined with an analysis of seismic reflection lines across the Ionian oVshore zone and information on historical earthquakes, in order to yield new constraints on active faulting in southeastern Sicily. This region, one of the most seismically active of the Mediterranean, is aVected by WNW‐ESE regional extension producing normal faulting of the southern edge of the Siculo‐Calabrian rift zone. Our data describe two systems of Quaternary normal faults, characterized by diVerent ages and related to distinct tectonic processes. The older NW‐SE-trending normal fault segments developed up to #400 kyr ago and, striking perpendicular to the main front of the Maghrebian thrust belt, bound the small basins occurring along the eastern coast of the Hyblean Plateau. The younger fault system is represented by prominent NNW‐SSE-trending normal fault segments and extends along the Ionian oVshore zone following the NE‐SW-trending Avola and Rosolini‐Ispica normal faults. These faults are characterized by vertical slip rates of 0.7‐3.3 mm yr’1 and might be associated with the large seismic events of January 1693. We suggest that the main shock of the January 1693 earthquakes (M~7) could be related to a 45 km long normal fault with a right-lateral component of motion. A long-term net slip rate of about 3.7 mm yr’1 is calculated, and a recurrence interval of about 550±50 yr is proposed for large events similar to that of January 1693.
140587264
New insights in the geodynamics of the Lipari–Vulcano area (Aeolian Archipelago, southern Italy) from geological, geodetic and seismological data
Abstract Geological, geodetic and seismological data have been analyzed in order to frame the Lipari–Vulcano complex (Aeolian archipelago, southern Italy) into the geodynamic context of the southeastern Tyrrhenian Sea. It is located at the northern end of a major NNW–SSE trending right-lateral strike-slip fault system named “Aeolian–Tindari–Letojanni” which has been interpreted as a lithospheric discontinuity extending from the Aeolian Islands to the Ionian coast of Sicily and separating two different tectonic domains: a contractional one to the west and an extensional one to the north-east. Structural field data consist of structural measurements performed on well-exposed fault planes and fractures. The mesostructures are mostly represented by NW–SE striking normal faults with a dextral-oblique component of motion. Minor structures are represented by N–S oriented joints and tension gashes widespread over the whole analyzed area and particularly along fumarolized sectors. The analyzed seismological dataset (from 1994 to 2013) is based on earthquakes with magnitude ranging between 1.0 and 4.8. The hypocenter distribution depicts two major alignments corresponding to the NNW–SSE trending Aeolian–Tindari–Letojanni fault system and to the WNW–ESE oriented Sisifo–Alicudi fault system. GPS data analysis displays ∼3.0 mm/yr of active shortening between the two islands, with a maximum shortening rate of about 1.0 × 10 −13  s −1 , between La Fossa Caldera and south of Vulcanello. This region is bounded to the north by an area where the maximum values of shear strain rates, of about 0.7 × 10 −13  s −1 are observed. This major change occurs in the area south of Vulcanello that is also characterized by a transition in the way of the vertical axis rotation. Moreover, both the islands show a clear subsidence process, as suggested by negative vertical velocities of all GPS stations which exhibit a decrease from about −15 to −7 mm/yr from north to south. New data suggest that the current kinematics of the Lipari–Vulcano complex can be framed in the tectonic context of the eastward migrating Sisifo–Alicudi fault system. This is dominated by transpressive tectonics in which contractional and minor extensional structures can coexist with strike-slip motion.
129414112
Roots of Etna volcano in faults of great earthquakes
Abstract Results from several seismic methods allow us to sketch the deep structure of Etna and its Ionian margin. Under Etna a volume of high velocity material is found in a structurally high position; the emplacement of this suggests spreading of the surrounding medium. Just offshore, down-to-the-east normal faults penetrate through the upper crust. The deeper crustal structure beneath appears upwarped from the basin towards Etna. Juxtaposed with the crust of Sicily, a thinner crust reaches from the Ionian Basin under Etna, and the mantle is upwarped. In such a structure, magma can then be viewed as a melted lens capping a mantle upwarp at shallow depth, rather than in an intracrustal chamber. This reduces the conflict between estimates of its volume from excess output of volatiles and short residence times. A link in time is indicated between volcanic and seismic activity at a large scale: over the millennium the reported ends of episodes of high output rates of magma are followed by the reported occurrences of magnitude 7 + earthquakes which caused destruction in southeastern Sicily. Several steep active normal fault have been imaged to a depth of 10 km the crust up to 30 km offshore of the cities of Catania and Augusta, which may be fault planes for such large earthquakes. They expand and prolongate the system of the Timpe faults on the eastern flank of Etna, thus linking large-scale tectonics offshore with the volcano. Etna developed together with normal faulting, upwarp, and spreading during the recent evolution of the former Ionian subduction. Activation of the material at depth at the lateral edge of the slab, by vertical motion with extension above, could produce the peculiar type of Etna magmatism.
4423107
The formation of Mount Etna as the consequence of slab rollback
Mount Etna, the largest volcano in Europe, lies close to the subduction-related Aeolian magmatic arc but shows no trace of subducted material in its magmas. Mount Etna is also situated on continental crust yet shows oceanic basalt affinities, with isotopic ratios of helium and carbon suggesting that it is fed by the same type of mantle source as are mid-ocean ridge basalts. Here we propose that although this giant volcano is not subduction-related—in the sense that it is not part of the magmatic arc—its formation is strongly related to the nearby subduction process. Based on a three-dimensional model of the tectonic plates in this region, we propose that the voluminous melting under Mount Etna results from ‘suction’ of asthenospheric material from under the neighbouring African plate. Such lateral flow is expected when descending slabs migrate backwards in the mantle (rollback) leaving low-pressure regions behind them. This was previously identified at the northern end of the Tonga arc (southwest Pacific Ocean) where such flow feeds arc or backarc magmatism. Here we show that in the south Tyrrhenian subduction zone, slab rollback pulls asthenospheric material much farther along the plate contact, reaching the base of the crust in the forearc region. This explains the voluminous melting under Mount Etna and also the recent uplift of the forearc region (the Calabrian peninsula).
51914312
Active faults and historical earthquakes in the Messina Straits area (Ionian Sea)
Abstract. The Calabrian Arc (CA) subduction complex is located at the toe of the Eurasian Plate in the Ionian Sea, where sediments resting on the lower plate have been scraped off and piled up in the accretionary wedge due to the African/Eurasian plate convergence and back arc extension. The CA has been struck repeatedly by destructive historical earthquakes, but knowledge of active faults and source parameters is relatively poor, particularly for seismogenic structures extending offshore. We analysed the fine structure of major tectonic features likely to have been sources of past earthquakes: (i) the NNW–SSE trending Malta STEP (Slab Transfer Edge Propagator) fault system, representing a lateral tear of the subduction system; (ii) the out-of-sequence thrusts (splay faults) at the rear of the salt-bearing Messinian accretionary wedge; and (iii) the Messina Straits fault system, part of the wide deformation zone separating the western and eastern lobes of the accretionary wedge. Our findings have implications for seismic hazard in southern Italy, as we compile an inventory of first order active faults that may have produced past seismic events such as the 1908, 1693 and 1169 earthquakes. These faults are likely to be source regions for future large magnitude events as they are long, deep and bound sectors of the margin characterized by different deformation and coupling rates on the plate interface.
129860139
Two-stage growth of the Calabrian accretionary wedge in the Ionian Sea (Central Mediterranean): Constraints from depth‐migrated multichannel seismic data
New structural images of the Calabrian accretionary wedge are presented from depth‐migrated multichannel seismic data. A combined interpretation swath‐mapping bathymetry allows us to identify five morphological domains on the basis of their tectonic style. (1) Beneath the undeformed Abyssal Plain, a set of deep, NW vergent reverse faults cuts the Ionian oceanic crust and thick pre-Messinian sediments. (2) Towards the NW, the low-taper post-Messinian wedge overlying a shallow NW dipping decollement, at the base of the Messinian evaporites and exhibiting strong tectonic thickening. (3) Beneath the flat Central Transition Zone, a backthrust marks the contact between the post- and pre-Messinian wedges. Here, the decollement dip increases (> 3°) cutting through deeper sediments to reach 10 km depth. (4) Beneath the pre-Messinian Calabrian wedge, some steep landward dipping features are imaged where underplating may occur. (5) Beneath the inner plateau, a fore‐arc basin lies above the top of the Calabrian continental basement imaged at 8 km depth. The architecture of the Calabrian accretionary complex is very similar to the Mediterranean Ridge. Both systems consist of (a) an external low-taper post-Messinian wedge overlying a thick undeformed section of underthrust Mesozoic sediments and (b) an internal pre-Messinian wedge where the decollement steps down and where the underthrust section is presumably underplated. We perform area balancing and show that since the Messinian, the Calabrian accretionary wedge has undergone extremely rapid outward growth at an average rate of 30 km/Ma, which makes it the fastest growing accretionary wedge over the past 5 Ma. 
 
Highlights: 
 
► Relation between the pre- and post-Messinian juxtaposed wedges. ► Contact between these wedges along a major backthrust. ► The 130 km long outer Calabrian prism: a huge salt-bearing body. ► One of the fastest growing wedges (2.0 cm/year) in recent Earth history. ►~ 170 km amount of post-Messinian subduction (subduction rate 3–4 cm/year).
128900656
Long‐term uplift rate of the Etna volcano basement (southern Italy) based on biochronological data from Pleistocene sediments
The eastern flank of Mt. Etna volcano rests on Pleistocene marine sediments, which unconformably cover the Apenninic–Maghrebian Chain units. A quantitative biostratigraphic analysis was carried out based on the calcareous nannofossil content of the Pleistocene deposits outcropping along the S and NE periphery of the volcano. Sediments were constrained to the MNN19e and MNN19f biozones, deposited from 1.2 to 0.589 Ma. According to the depth of deposition and the present altitude of the Pleistocene succession, uplift rates are estimated between 1.1 and 1.7 mm yr−1 for the northeastern sector of the Etna edifice, and between 0.36 and 0.61 mm yr−1 for the southern one. This inhomogeneous long-term uplift rate affecting the Etna region, probably results from a buried thrust below the northern flank of Etna, which is related to the post-Tortonian geodynamic evolution of NE Sicily.
129920963
Paleo-environmental and volcano-tectonic evolution of the southeastern flank of Mt. Etna during the last 225 ka inferred from the volcanic succession of the ‘Timpe’, Acireale, Sicily
Abstract The tectonic escarpments locally known as ‘Timpe’ cut a large sector of the eastern flank of Etna, and allow an ancient volcanic succession dating back to 225 ka to be exposed. Geological and volcanological investigations carried out on this succession have allowed us to recognize relevant angular unconformities and volcanic features which are the remnants of eruptive fissures, as well as important changes in the nature, composition and magmatic affinity of the exposed volcanics. In particular, the recognition in the lower part of the succession of important and unequivocal evidence of ancient eruptive fissures led us to propose a local origin for these volcanics and to revise previous interpretations which attributed their westward-dipping to the progressive tectonic tilting of strata. These elements led us to reinterpret the main features of the volcanic activity occurring since 250 ka BP and their relationship with tectonic structures active in the eastern flank of Etna. We propose a complex paleo-environmental and volcano-tectonic evolution of the southeastern flank of Mt. Etna, in which the Timpe fault system played the role of the crustal structure that allowed the rise and eruption of magmas in the above considered time span.
127150579
The volcano-tectonic map of Etna volcano, 1:100.000 scale:an integrated approach based on a morphotectonic analysisfrom high-resolution DEM constrained by geologic,active faulting and seismotectonic data
A new volcano-tectonic map of Etna volcano has been compiled 
through a morphotectonic analysis performed with detailed field 
mapping, high-resolution DEM and orthoimages, constrained by 
seismotectonic data. In this study, we present a homogeneous mapping 
of the volcano-tectonic and tectonic elements on the whole volcano, 
consistent with the updated knowledge on the geology and 
active tectonics observed in historical times. Details of the tectonic 
features occurring in the lower-middle part of the volcanic edifice, 
namely the more densely urbanized areas, are described; volcanic 
elements such as eruptive fissures, caldera and flank collapse rims 
affecting the upper sectors, are also reported. All the volcanic landforms 
of Etna edifice have been generated by constructive and 
destructive volcanic processes largely during the last 15 ka activity of 
Mongibello volcano. DEM-derived images (e.g. slope and aspect 
maps) were produced and interpreted in order to identify faultrelated 
surface features based on an explicit list of well-known elements 
of tectonic geomorphology. Subsequently, the morphotectonic 
mapping has been compared with field data on geologic 
marker offsets, as well as evidence of surface faulting, including 
coseismic displacements and creeping of historical and recent 
events. This combined approach has enabled classifying each element 
reported in the map as (i) exposed faults, (ii) buried faults and 
(iii) hidden faults. The analysis of slip-rates confirms the exceptional 
dynamics of the Pernicana fault, which is characterised by an almost 
constant slip-rate of 20-36 mm/a over the last 1000 years, while the 
Timpe fault zone and the structural system in the southern flank 
accommodate a relevant amount of deformation with slip-rates 
reported to range of ca. 2-4 mm/a. Finally, a seismotectonic model summarises 
the information regarding seismic hazard, with reference to 
the additional, potentially severe effects induced by surface faulting.
134054978
Macroseismic catalogue of Mt. Etna earthquakes from 1832 to 1998
A catalogue of the earthquakes which have produced macroseismic effects in the Etnean area during the 1832-1998 period is presented. The motivation for creating a catalogue specifically for this region derives from the fact that the traditional parametric catalogues do not allow a detailed characterisation of seismicity, for instance in terms of seismic sequences or seismotectonic analyses. The quantity and the quality of available historical information for the area allow to investigate these aspects. The performed analysis has permitted to associate about 550 earthquakes with seismogenic structures so that it is possible to investigate fault behaviour in time. The catalogue has been compiled through the analysis of some 200 contemporaneous sources (scientific papers, bulletins, newspapers and archive documents) and the intensities assessed by using the EMS-98 macroseismic scale. The catalogue lists 1735 events in all. 
For each event the focal parameters are defined: epicentral location, maximum and epicentral intensities, macroseismic magnitude, when possible seismogenic fault and coseismic surface faulting; instrumental values of magnitude and depth are also reported. Tests on determination of the epicentral coordinates and some examples of possible use and application of the catalogue dataset are presented. The attached CD-ROM, which includes a database of 7325 macroseismic observations, is a searchable catalogue for epicentres and intensity maps of all the events. In addition, the following queries can be performed: selection of earthquakes by date, intensity and coordinates; reconstruction of the seismic histories for 426 localities in the Etna area.
102483399
Buried active faults in the Zafferana Etnea territory (south-eastern flank of Mt. Etna): geometry and kinematics by earthquake relocation and focal mechanisms
We relocated seismicity that occurred from 2000 to 2005 inside a sector of Mt. Etna, comprising the town of Zafferana Etnea, using the double-difference technique. This approach revealed some spatial clusters of events at depths of 3.0 km to 5.5 km b.s.l., which suggested NE-SW-oriented and NNW-SSE-oriented active structures located west and north-west with respect to Zafferana Etnea. We also calculated 64 fault plane solutions, and azimuth and dip distributions of maximum compression P axes. The data include eight events with magnitudes between 3.1 and 3.7 that caused damage to Zafferana Etnea. This approach has allowed the definition of the geometry of structures that show no surface evidence, but are potentially hazardous for this territory. These faults might be linked to the regional tectonics, although they were activated by stress changes related to a general pressurizing of the Mt. Etna magma system between 2000 and 2005.
129716715
Coastal elevation changes in eastern Sicily: implications for volcano instability at Mount Etna
Abstract The eastern flank of Mount Etna, Sicily has been recognized as being unstable, and three contrasting models have been proposed to account for this phenomenon, these being deep-seated spreading, shallow sliding and tectonic block movements. These models are examined by making reference to the rates and patterns of crustal movement along the eastern coastline of Sicily as determined from palaeoshoreline data. The south-eastern coastline of Sicily (Portopalo to Catania) provides no evidence of Holocene emergence. In contrast the volcanic coastline (Catania to Capo Schiso) and the northeastern shoreline (Taormina to Milazzo) display widespread evidence of coastal emergence. Radiocarbon dated remains indicate that both the volcano and northeastern Sicily have been uplifted at a rate exceeding 1.5 mm a−1 during Holocene times, although more recent rates of uplift may have been greater. The pattern of uplift suggests that the northeastern coastline of Sicily, including the volcanic edifice, is apparently uplifting as a coherent unit, with superficial flank movements being superimposed on a regionally uplifting sub-volcanic basement.
128984902
Holocene coastal uplift in the taormina area, northeastern sicily: Implications for the southern prolongation of the calabrian seismogenic belt
Elevated erosional notches and emergent marine deposits developed on limestone headlands along the Taormina coastline of northeastern Sicily testify to recent shoreline uplift. Although located at the southern prolongation of the Calabrian seismogenic belt, a zone of active extensional tectonics and rapid late Quaternary uplift, the study area lacks historical and instrumental evidence for significant earthquakes. A prominent notch level at an elevation of +4.5 and +5.0 m at Mazzaro and Capo Sant'Alessio, respectively, is dated by 14C assay of associated marine boring molluscs (Lithophaga) to be coincident with the 5000 yr BP deceleration of global eustatic rise, the mid-Holocene quasi-stillstand. These first radiometric dates of Holocene emergence along the northeastern Sicily coast indicate time-averaged uplift rates of 1.1 – 1.8 mm/yr. Well-defined erosional notches postdating the mid-Holocene quasistillstand, however, imply coastal uplift was not gradual but instead involved occasional abrupt crustal movements, probably the result of large paleoseismic earthquakes along the coastal-bounding normal faults. The results support a need for a re-evaluation of the earthquake potential of the Sicilian sector of the Apenninic seismogenic belt.
131018329
Holocene sea-level change in Sicily and its implications for tectonic models: new data from the Taormina area, northeast Sicily
The northeast coast of Sicily shows emergent marine features that have been uplifting during the Holocene along the footwalls of two major regional fault systems, the Malta Escarpment and Messina fault system. Previously, uplift rates were interpreted as up to about 1.8 mm/mm a−1. New dates on shelly remains, collected close to sea-level, from the Taormina area north of Mount Etna, and amended sea-level curves, are used to show that uplift over the past 6000 years has been proceeding at a slower rate of about 1.4 mm a−1. However, over a longer time period, from the Tyrrhenian Oxygen Isotope Stage 5.5 (about 125 ka) to the present day, the uplift rate has been yet slower, at about 1 mm a−1. Northeast Sicily lies in a complex plate boundary region whereas, in contrast, the rest of Sicily appears to have been stable throughout the later Quaternary. Further comparisons show that the French Mediterranean coast [Lambeck, Bard (2000) Earth Planet. Sci. Lett., 175, 202–222] is a region of crustal stability, where movement is dominated by subsidence of the outer portion of the proglacial forebulge of the last glaciation. There the coastline has been progressively submerged during the Holocene, and sea level has never been higher than at present. Northeastern Sicily uplift is therefore more likely controlled by plate processes that mask most of the effects of glacio-hydro-isostatic adjustment.
140683806
Geological and geomorphological evolution of the Etna volcano NE flank and relationships between lava flow invasions and erosional processes in the Alcantara Valley (Italy)
Abstract In this paper, the interrelationships between volcanic activity and fluvial events in the Alcantara Valley are investigated. Based on the correlation between the stratigraphy of the NE flank of Mt Etna and subsurface data, the geological and geomorphological evolutions of the valley are reconstructed. New 1:10 000 scale geological mapping shows that the bulk of this sector of the volcano is made up of the Ellittico volcano lava flows, though they are widely covered by the products of the eruptive activity of the last 15 ka. The present-day morphological setting of the Alcantara Valley is the result of two main evolutionary phases initiated during the activity of the Ellittico volcano. Only one lava flow invasion of the valley floor occurred in the first phase. This phenomenon was followed by a long period of erosional processes leading to the entrenchment of the drainage pattern and the erosion of the Ellittico lava flow. About 20–25 ka ago, an important change in the frequency of the lava flow invasions into the valley occurred associated with the final stage of the Ellittico volcano activity marking the beginning of the second phase. During this phase, volcanic processes became predominant with respect to other morphogenetic processes in the Alcantara Valley. Lava flows coming from the NE flank of the Ellittico volcano caused a radical modification of the morphological setting of this area, even though only one lava flow emitted by an eruptive fissure located within the valley partially filled the riverbed. During the eruptive activity of the last 15 ka, the complete filling of the Alcantara Valley floor occurred. In particular, between 15 and 7 ka, a lava flow originated from the Mt Moio scoria cone filled the valley floor for a distance of about 9 km. Following a short period of erosion, an eruptive fissure located within the valley generated a 20–21-km-long lava flow that was channelled along the full extent of the Alcantara Valley and stretches for about 3 km offshore in the Ionian sea. In the last 7 ka, lava flows originating from the NE-Rift zone produced only temporary damming of the riverbed without any important contribution to the filling of the Alcantara Valley.
128415484
Raised Holocene paleo-shorelines along the Capo Schisò coast, Taormina: New evidence of recent co-seismic deformation in northeastern Sicily (Italy)
Abstract Detailed mapping of geomorphological, biological and archaeological sea-level markers around the Capo Schiso volcanic headland, a few kilometers south of Taormina, north-eastern Sicily, has documented the occurrence of three Holocene paleo-shorelines raised at different altitudes. The uppermost shoreline (PS1) is represented by a fossiliferous beach deposit that is heavily eroded and only few small sections, at elevations ranging between ∼3 and ∼5 m above the present sea-level, are visible. The middle shoreline (PS2) was found at a maximum altitude of ∼3 m and is represented by algal rims, remnants of barnacle bands and vermetid concretions, and by a fossiliferous beach deposit. The lowermost shoreline (PS3) includes remnants of algal rims, vermetid concretions, fossil barnacle bands and a beachrock, and reaches an elevation of 1.60–1.80 m. New radiocarbon dating results, integrated with published ages from nearby paleo-shoreline outcrops, constrains for the Taormina region an average uplift rate of 1.7–1.8 mm/yr in the last 5 ka, and the occurrence of three co-seismic uplift events at 4.4–3.9 ka, 2.1–1.8 ka and ≤1.0 ka ago. Abrupt displacements are tentatively attributed to footwall uplift along an offshore normal fault, but further investigations are needed to better constrain the causative source of past earthquakes. Notwithstanding, based on coastal tectonic analysis, this paper provides a new assessment of age and recurrence time of Holocene earthquakes in a historically strong seismogenic area.
128810315
The deformation offshore of Mount Etna as imaged by multichannel seismic reflection profiles
Abstract Despite the clear evidence of active flank dynamics that is affecting the eastern side of Mount Etna, the contribution of tectonic processes has not been yet understood. So far, the various models proposed to explain the observed flank deformation have been based on onshore structural data, coming from the volcanic edifice. The Ionian offshore of Mount Etna has been only recently investigated using multichannel seismic profiles, and offers the opportunity to image the structural features of the substrate of the unstable flank of the volcano. This contribution aims at describing the deformation located offshore Mount Etna using multichannel seismic profiles recently acquired during three seismic surveys. The onshore flank deformation of Mount Etna appears to be laterally confined by two tectonic guidelines, trending roughly E–W, located to the north and south of the deforming flank; the northern guideline, in particular, takes the surface expression of a sharp fault (Pernicana Fault). Though often assumed that these boundary structures continue offshore as linear features, connected to a frontal thrust ramp, the occurrence of this simple offshore structural system has not been imaged. In fact, seismic data show a remarkable degree of structural complexity offshore Mount Etna. The Pernicana Fault, for instance, is not continuing offshore as a sharp feature; rather, the deformation is expressed as ENE–WSW folds located very close to the coastline. It is possible that these tectonic structures might have affected the offshore of Mount Etna before the Pernicana Fault system was developed, less than 15 ka ago. The southern guideline of the collapsing eastern flank of the volcano is poorly expressed onshore, and does not show up offshore; in fact, seismic data indicate that the Catania canyon, a remarkable E–W-trending feature, does not reflect a tectonic control. Seismic interpretation also shows the occurrence of a structural high located just offshore the edifice of Mount Etna. Whereas a complex deformation affects the boundary of this offshore bulge, it shows only limited internal deformation. Part of the topography of the offshore bulge pre-existed the constructional phase of Mount Etna, being an extension of the Hyblean Plateau. Only in the northern part, the bulge is a recent tectonic feature, being composed by Plio-Quaternary strata that were folded before and during the building of Mount Etna. The offshore bulge is bounded by a thrust fault that can be related to the intrusion of the large-scale magmatic body below Mount Etna.
128672398
Volcano-tectonic activity along structures of the unstable NE flank of Mt. Etna (Italy) and their possible origin
Abstract We describe the prehistoric–historic activity of the main and minor volcano-tectonic structures of the northeastern flank of Mt. Etna, giving new data which provide a clearer view of how destabilized volcanoes react to magma pressure and gravity forces. Data are mostly based on new lithostratigraphic surveys and on offset measurements of late Pleistocene–Holocene deposits and historic man-made features. The North-East Rift (NE Rift) is a volcanic rift that has guided mostly explosive, but also secondary effusive, activity since the end of the Pleistocene. Monogenetic cones and explosive craters are strongly elongated and aligned along 66 main surface fractures and several others, hidden, but inferred, from sinkhole alignments. The opening direction is locally oblique, with a left-lateral component in the north-eastern segment of the rift. At the NE tip of the rift, the movements are relieved by the normal left-lateral Pernicana Fault (PF), an 11-km-long structure comprising E–W fault segments connected by right-stepping en echelon faults. Our study demonstrates that the very high slip rates at a centennial scale of these structures are well constrained and similar (NE Rift=0.6–1.8 cm/a, PF=0.5–2.2 cm/a) and have been also recognized in the Latest Pleistocene–Holocene (2.7 cm/a). The E–W Fiumefreddo Fault (FF) has normal left-lateral kinematics and a historic slip rate of 0.1 cm/a. Ripa della Naca Faults strike NE and are covered by unfaulted
126795830
Geophysical investigation of Pleistocene volcanism and tectonics offshore Capo Vaticano (Calabria, southeastern Tyrrhenian Sea)
Abstract Magma upwelling forming volcanic plumbing systems in back arc settings is typically controlled by extensional tectonic structures of the upper crust. Here we investigate this process in the area between the volcanic arc of the Aeolian Islands and the Calabrian arc (SE Tyrrhenian Sea) by integrating morpho-bathymetry and reflection seismic data with the outcomes of “Inverse 3D magnetic modeling” of previously gathered aeromagnetic data. Morpho-bathymetric data highlight the presence of a seamount ∼10 km offshore Capo Vaticano Promontory (eastern Calabria). This feature, named Capo Vaticano seamount is composed of a series of NE-trending ridges, the greatest of which (R1) is ∼12 km long, and 2.4 km wide, displays asymmetric flanks with a landward steep slope, oblique morphological steps and elongated NE-trending rims. The position of the R1 ridge summit fits the Reduced-to-the-Pole peak of a high-intensity magnetic anomaly straddling Capo Vaticano Promontory and its offshore prolongation. Seismic and bathymetric data highlight two extensional fault systems affecting the offshore of Capo Vaticano Promontory during the Plio-Pleistocene: (a) a Pliocene NW-trending, SW-dipping normal fault system, and (b) a Pleistocene NE-trending, SE-dipping normal fault system. The younger system is composed of a series of en-echelon branching normal faults bounding the eastern side of the R1 ridge. Aeromagnetic data modeling imaged a complex 3D-magnetized body below the R1 ridge exhibiting a sub-vertical conduit-like structure in the shallow part, and a NE-striking, sheet-like shape inclined by 45° in depth. The location of the sub-vertical conduit coincides with the summit of the R1 ridge. The magma uprising at the root of the volcano was controlled by the Pliocene NW-trending faults whereas its further upwards migration was ostensibly controlled by the Pleistocene NE-trending faults. Both fault systems are responsible for the high level of fracturing that likely favored the upward migration of magma. The younger extensional systems also controls the present-day, mantle derived, fluid escapes observed at the summit of the R1 ridge. Relying on seismic stratigraphic evidence as well as the normal polarity of the magnetic anomaly, the R1 ridge probably started to form during the Olduvai chron (early Pleistocene, 1.81–1.96 Ma). Accordingly, the Capo Vaticano volcano may represent the result of magmatic activity that predates the Aeolian volcanic arc.
128674381
Use of high-frequency (3.5–12 kHz) echograms in the study of near-bottom sedimentation processes in the deep-sea: A review☆
During the past 15 years in creasing numbers of studies have demonstrated that continuous echograms recorded on high-frequency (3.5–12 kHz) precision depth recorders aboard surface ships provide a valuable tool for the study of near-bottom sedimentation processes on the deep-sea floor. By constructing an echo character map of the various types of bottom echoes recorded in a region and combining this information with additional data (cores, bottom photographs, nephelometer, hydrographic and temperature), it is often possible to determine the types and regional influence of the various sedimentation processes (e.g., contour currents, turbidity currents, slumps and debris flows) which have shaped that region. The types and distributions of bottom echoes from most of the basins of the Atlantic as well as for several regions of the western Indian Ocean and the western Pacific have now been classified and mapped on a regional scale. Each of these regions returns several discrete types of echoes; most types are similar from basin to basin as well as ocean to ocean. In this paper a few examples of previous echo character studies are reviewed in order to illustrate how high-frequency echograms can be utilized to study near-bottom processes. 
 
(1) Regional echo-character maps often reveal the distribution and abundance of sediments deposited by down-slope processes such as turbidity currents. Three echo types which are widespread throughout most basins of the world show a qualitative correlation with the relative abundance of coarse, bedded turbidites (silt, sand, and gravel) in the upper few meters of the sea floor: (a) distinct echoes with continuous sub-bottoms are recorded from regions with little or no coarse sediment; (b) regions with moderate amounts of silt/sand return semi-prolonged echoes with intermittent or discontinuous sub-bottoms; and (c) regions with large amounts of silt/sand return very prolonged echoes with no sub-bottoms. 
 
(2) A wide variety of hyperbolic bottom echoes are recorded from regions of the sea floor where sedimentation is controlled by deep thermohaline flow (contour currents). These hyperbolic echoes are returned by erosional/depositonal bed forms such as non-migrating sediment waves and erosional furrows. Such regions of hyperbolic echoes are often clearly distributed beneath strong near-bottom thermohaline currents such as the Antarctic Bottom Water. Thus the distributions of these types of echoes often show the regional influence of contour currents. In addition to the hyperbolic echoes, a variety of undulating, quasi-hyperbolic echoes with shifting, non-conformable or truncated sub-bottoms are also often recorded. These bedforms appear to be migrating sediment waves and are generally observed in regions affected by contour currents. In some cases, however, it appears that turbidity currents also form such migrating waves. 
 
(3) Echograms have also been of great value in revealing the presence and distribution of mass-wasting processes such as slumps, slides and debris flows. Such deposits generally appear as convex, lense-shaped transparent layers which return a fuzzy, prolonged bottom echo. Often undisturbed, well-stratified sediments are visible below the deposits as are scarps and displaced blocks at the head of the slump complex. Echograms have revealed slump/debris-flow complexes ranging from 30,000 km2 in size. 
 
High-frequency echograms are thus an extremely valuable tool for studying the marine geology, sediment types, and near-bottom sedimentation processes active on the sea floor. Although widely spaced data lines in many regions can only define various sedimentary processes and bedforms on a broad regional scale, such data often indicate the best locations for concentrating more detailed and quantitative studies using closely spaced surveys and sophisticated instrument packages (e.g., Deep-tow, GLORIA, submersibles, etc.). Often only the detailed studies such as these can reveal the true shapes, origins, and hydrodynamic setting of various bedforms which return specific echo types on surface-ship echograms. In addition, most echocharacter studies to date have been qualitative. In the future more sophisticated, quantitative studies will be necessary in order to fully interpret and utilize the information contained in surface-ship echograms.
129552346
Sea level change along the Italian coast during the Holocene and projections for the future
Published and new sea level data are used to provide projections of sea level change in Italy for the year 2100 by adding new isostatic and tectonic component to the IPCC and Rahmstorf projections. Comparison of the observations from more than 130 sites (with different geomorphological and archaeological sea level markers) with the predicted sea level curves provides estimates of the vertical tectonic contribution to the relative sea level change. The results are based on the most recent ANU model for the ice sheets of both hemispheres, including an alpine deglaciation model. On the basis of the eustatic, tectonic and isostatic components to the sea level change, projections are provided for marine inundation scenarios for the Italian coastal plains for the year 2100, that today are at elevations close to current sea level.
46895266
A Late Pleistocene sea level stack
Abstract. Late Pleistocene sea level has been reconstructed from ocean sediment core data using a wide variety of proxies and models. However, the accuracy of individual reconstructions is limited by measurement error, local variations in salinity and temperature, and assumptions particular to each technique. Here we present a sea level stack (average) which increases the signal-to-noise ratio of individual reconstructions. Specifically, we perform principal component analysis (PCA) on seven records from 0 to 430 ka and five records from 0 to 798 ka. The first principal component, which we use as the stack, describes  ∼  80 % of the variance in the data and is similar using either five or seven records. After scaling the stack based on Holocene and Last Glacial Maximum (LGM) sea level estimates, the stack agrees to within 5 m with isostatically adjusted coral sea level estimates for Marine Isotope Stages 5e and 11 (125 and 400 ka, respectively). Bootstrapping and random sampling yield mean uncertainty estimates of 9–12 m (1σ) for the scaled stack. Sea level change accounts for about 45 % of the total orbital-band variance in benthic δ18O, compared to a 65 % contribution during the LGM-to-Holocene transition. Additionally, the second and third principal components of our analyses reflect differences between proxy records associated with spatial variations in the δ18O of seawater.
140561362
Sea level at the last glacial maximum, constrained by oxygen isotopic curves of planktonic foraminifera in the Japan Sea
The Japan Sea is connected with the Okhotsk Sea and Northwest Pacific through three straits, viz. Mamiya (Tartarskiy), Soya and Tsugaru, and with the East China Sea through Tsushima Strait, all having sill depths of 3% recorded in the MIS 3-4 sections of the studied cores. This observation indicates nearly similar surface water conditions in the Japan Sea during both the previous glacial maxima, and hence suggests negligible effect of strait tectonics on the sea level since the last 140 ka. Low d 18 OPF values with small amplitude are also observed at the cold stage MIS 6.4, but not observed at another cold stage MIS 4.2. This observation suggests that the low-salinity surface water in the Japan Sea started to develop at the sea level between MIS 4.2 and 6.4. Judging from the cross-section of the Tsushima Strait and the sea floor topography of the East China Sea, the sea level between MIS 4.2 and 6.4 must have been between 90 m and 100 m below the present. From a proportional relationship between the standard d 18 O curve (LR04) in deep-sea cores and globally averaged sea-level change, the eustatic sea level obtained for the LGM is 120 � 7 m below the present. Thus the Japan Sea, in a far-field location from the continental ice sheets, provides an important clue for estimation of the eustatic sea level at the LGM. Copyright # 2012 John Wiley & Sons, Ltd.
129198718
Dansgaard‐Oeschger and Heinrich event imprints in Alboran Sea paleotemperatures
Past sea surface temperature (SST) evolution in the Alboran Sea (western Mediterranean) during the last 50,000 years has been inferred from the study of C37 alkenones in International Marine Global Change Studies MD952043 core. This record has a time resolution of ∼200 years allowing the study of millennial-scale and even shorter climatic changes. The observed SST curve displays characteristic sequences of extremely rapid warming and cooling events along the glacial period. Comparison of this Alboran record with δ18O from Greenland ice (Greenland Ice Sheet Project 2 core) shows a strong parallelism between these SST oscillations and the Dansgaard-Oeschger events. Five prominent cooling episodes standing out in the SST profile are accompanied by an anomalous high abundance of Neogloboquadrina pachyderma sinistral which is confined to the duration of these cold intervals. These features and the isotopic record reflect drastic changes in the surface hydrography of the Alboran Sea in association with Heinrich events Hl–5.
129647476
Structure of mud volcano systems and pockmarks in the region of the Ceuta Contourite Depositional System (Western Alborán Sea)
Abstract New high-resolution seismic and swath bathymetry data reveal the detailed structure of nine mud volcanoes and two large fields of pockmarks at water depths of 400–1100 m in the western Alboran Sea. These features are related to episodes of focused fluid flow through Pliocene-Quaternary contourite deposits of the Ceuta Drift. We describe nine mud volcano systems, composed of two key structural elements: (i) extrusive edifices comprising cones, bicones and low-dip mudflows interfingering with adjacent drift sediments and (ii) intrusive feeder complexes comprising pipes and unstratified downward-tapering cones underlying the extrusive edifices. The mud volcano systems are grouped into four types: I: Complex edifices; II: Stacked single edifices; III: Single edifices fed by buried bicones and IV: Single edifices. All except the last record episodic extrusive activity since the Pliocene, the timing of which is constrained by correlation between the main mud extrusion episodes and dated unconformities within the Ceuta Drift. Complex mud volcanoes composed of twin to multiple seabed cones are the longest-lived systems, with at least six extrusive episodes since the mid-Pliocene; most of the mud volcanoes appear to have been reactivated in the mid-Pleistocene (~ 0.9 Ma, MPR discontinuity) and all at MIS12 (0.4 Ma). While the onset of focused fluid flow was triggered by mid-Pliocene tectonically-driven diapirism of Lower Miocene shales that form the rooting zone of the mud volcanoes, we suggest that some of the Pleistocene phases of mud extrusion might be related to erosion of the contourite drift during major sea-level falls. In addition to vertical focused fluid flow, we propose that leakages from the mud volcano feeder complexes into high-permeability contourite sediments may cause lateral fluid migration and form gas accumulations. Lateral fluid flow in the near surface sediments could be responsible of forming subsurface reservoirs and consequently, random pockmarks by fluidification and/or liquefaction of the non-consolidated shallow sediments. Stacked buried paleo-pockmarks indicate that this mechanism has been persistent along recent times, at least after the mid-Pleistocene.
129384465
Plio–Quaternary tectonic evolution and structure of the Catania foredeep, the northern Hyblean Plateau and the Ionian shelf (SE Sicily)
Abstract Available multi- and single-channel seismic reflection profiles, calibrated by onshore borehole data, have been used for defining the structural styles in the shelf and slope of the Ionian Sea between Catania and Augusta (SE Sicily). The geological and geophysical data suggest that this area represents a segment of the foredeep–foreland system which collapsed after Late Pliocene times. The foundering was controlled by normal faults trending NE–SW, which flank the southern margin of the Catania foredeep. Onland, in outcrop, these faults appear largely to be post-dated by Lower Pleistocene sediments, nearshore carbonates passing laterally into basinal clays, which lie unconformably upon older substrata. Offshore, close to the southern edge of the foredeep, seismic lines allow recognition of two distinct units: a syn-rift wedge (Upper Pliocene submarine tholeiites and sediments), and a post-rift sequence which can be correlated with Lower Pleistocene carbonates, sands and clays recognisable on land, both in outcrop and by borehole data. The true frontal part of the thrust belt, as detected by the seismic lines, occupies the inner part of the area investigated and is buried by Upper Pliocene and Lower Pleistocene sediments. However, the compressive deformation seems to propagate toward the south-southeast by means of growing detachment levels developing at depth within Pleistocene marine clays, for a length of about 10 km, ahead of the present-day thrust front. Offshore, the faults trending NE–SW are dissected towards the east by faults trending NNW–SSE, subparallel to the Malta Escarpment, which flank the edge of the submerged Messina Rise. These faults, originating in a steep scarp which drops eastwards to the deep Ionian basin, have triggered submarine slides and affected the present-day seafloor sediments. As shown by seismic lines and as stressed by the modern seismicity of the area, some of the faults along the Malta Escarpment could be still active.
73655407
Evidences of a contractional pattern along the northern rim of the Hyblean Plateau (Sicily, Italy) from GPS data
In this paper we present the main results inferred from GPS data collected between 1998.00 and 2009.78 along the northern rim of the Hyblean Plateau from 9 continuous and 23 survey-mode sites. From a geological point of view, this area is of great interest because 1) it represents an important piece of the collision front between Nubia and Eurasia 2) it is very close to the biggest European volcano Mount Etna and 3) it has been hit by strong earthquakes in the past (1169 and 1693) that struggled the cities of Catania, Siracusa and Ragusa provoking tens of thousands of casualties. We have found that the ground deformation pattern clearly defines an area of prevailing contraction along the northern rim of the Hyblean Plateau with a maximum negative strain-rate of about 0.14µstrain/yr in agreement with both geological and Interferometric Synthetic Aperture Radar (InSAR) data. In addition, a transition to extensional regime is acting toward the central sector of the plateau. The velocity field referred to the Eurasian frame indicates that a large part of the plateau is dominated by a 5.4mm/yr northward motion.