Southern Tyrrhenian Area Research Articles

The Response of Sandstone Sea Cliffs to Holocene Sea-Level Rise by Means of Remote Sensing and Direct Surveys: The Case Study of Punta Licosa Promontory (Southern Italy)

Punta Licosa promontory is located in the northern part of the Cilento coast, in the southern Tyrrhenian basin. This promontory is bordered by sea cliffs connected to a wide shore platform sloping slightly towards the sea. This area has been considered stable at least since Late Pleistocene, as testified by a series of evidence well known in the literature. The aim of this research is to reconstruct the main coastal changes that have occurred in this area since the middle Holocene by means of the literature data, aerial photo interpretation, satellite images, GPS measurements, direct underwater surveys, GIS elaborations of high-resolution DTMs, bathymetric data and high-resolution orthophotos taken by UAV. Particular attention was paid to the wide platform positioned between −7.2 ± 1.2 m MSL and the present MSL, this being the coastal landform interpreted as the main consequence of sea cliff retreat. The elevation of this landform was compared with the GIA models calculated for the southern Tyrrhenian area, allowing establishing that it was shaped during the last 7.6 ± 1.1 ky BP. Moreover, the interpretation of archaeological and geomorphological markers led to the reconstruction of the shoreline evolution of this coastal sector since 7.6 ky BP. This research evaluates the cliff retreat under the effect of Holocene RSL variation on Cilento promontories, located in the western Mediterranean and characterised by the presence of monophasic platforms, and the applied method can be considered more effective and less complex and expensive if compared to other effective approaches such as those based on the usage of cosmogenic nuclides.

New insights on volcanic and tectonic structures of the southern Tyrrhenian (Italy) from marine and land seismic data

We present results from the first crustal seismic tomography for the southern Tyrrhenian area, which includes ocean bottom seismometer (OBS) data and a bathymetry correction. This area comprises Mt. Etna, the Aeolian Islands, and many volcanic seamounts, including the Marsili Seamount. The seismicity distribution in the area depends on the complex interaction between tectonics and volcanism. The 3‐D velocity model presented in this study is obtained by the inversion of P wave arrival times from crustal earthquakes. We integrate travel time data recorded by an OBS network (Tyrrhenian Deep Sea Experiment), the SN‐1 seafloor observatory, and the land network. Our model shows a high correlation between the P wave anomaly distribution and seismic and volcanic structures. Two main low‐velocity anomalies underlie the central Aeolian Islands and Mt. Etna. The two volumes, which are related to the well‐known active volcanism, are separated and located at different depths. This finding, in agreement with structural, petrography, and GPS data from literature, confirms the independence of the two systems. The strongest negative anomaly is found below Mt. Etna at the base of the crust, and we associate it with the deep feeding system of the volcano. We infer that most of the seismicity is generated in brittle rock volumes that are affected by the action of hot fluids under high pressure due to the active volcanism in the area. Lateral changes of velocity are related to a transition from the western to the central Aeolian Islands and to the passage from continental crust to the Tyrrhenian oceanic uppermost mantle.

Modeling ground deformations of Panarea volcano hydrothermal/geothermal system (Aeolian Islands, Italy) from GPS data

Panarea volcano (Aeolian Islands, Italy) was considered extinct until November 3, 2002, when a submarine gas eruption began in the area of the islets of Lisca Bianca, Bottaro, Lisca Nera, Dattilo, and Panarelli, about 2.5 km east of Panarea Island. The gas eruption decreased to a state of low degassing by July 2003. Before 2002, the activity of Panarea volcano was characterized by mild degassing of hydrothermal fluid. The compositions of the 2002 gases and their isotopic signatures suggested that the emissions originated from a hydrothermal/geothermal reservoir fed by magmatic fluids. We investigate crustal deformation of Panarea volcano using the global positioning system (GPS) velocity field obtained by the combination of continuous and episodic site observations of the Panarea GPS network in the time span 1995–2007. We present a combined model of Okada sources, which explains the GPS results acquired in the area from December 2002. The kinematics of Panarea volcano show two distinct active crustal domains characterized by different styles of horizontal deformation, supported also by volcanological and structural evidence. Subsidence on order of several millimeters/year is affecting the entire Panarea volcano, and a shortening of 10−6 year−1 has been estimated in the Islets area. Our model reveals that the degassing intensity and distribution are strongly influenced by geophysical-geochemical changes within the hydrothermal/geothermal system. These variations may be triggered by changes in the regional stress field as suggested by the geophysical and volcanological events which occurred in 2002 in the Southern Tyrrhenian area.

An improved seismicity picture of the Southern Tyrrhenian area by the use of OBS and land-based networks: the TYDE experiment

The problem of large location uncertainties for seismicity occurring in the Southern Tyrrhenian Sea have been partially exceeded during the implementation of the long-term scientific mission of the TYrrhenian Deep sea Experiment (TYDE), which allowed the installation of 14 wide-band Ocean Bottom Seismometers (OBS) and Hydrophones (OBH) in the period December 2000 – May 2001 on the sea-bottom floor around the Aeolian and Ustica Islands. Local events recorded at landstations have been observed also on the seismograms of the Ocean Bottom Seismic Network (OBSN). Moreover, some hundreds of low magnitude events, undetected from the land networks, have been recorded. We combined the readings of body wave arrival times from OBS-OBH with those from landstations to localise seismic events. We focused our study on three clusters of events representative of the seismic activity of the area: (i) “deep” events, (ii) Ustica (iii) NE-Sicily. The analysis of the integrated data set of the seismicity off-shore and on-shore, obtained from the combined land-OBS seismic network (Ustica sequence and Deep events), has improved locations in terms of RMS residuals, azimuthal gap, epicentral and hypocentral errors. Moreover, further classes of events have been analysed: the first one includes some local events that could be located only by integrating single trigger readings from the few available land-stations with the OBSN-data; the second one comprises local events that have been detected only by the OBS-OBH stations. In particular, the last cluster underlines the importance of an OBSN in the Tyrrhenian deep basin to reveal its unknown intense micro-seismicity, permitting to better understand both the tectonic and geodynamic picture of the area.

Crustal magnetism of the Southern Tyrrhenian Sea from aeromagnetic surveys

Abstract Aeromagnetic data from the Southern Tyrrhenian Sea have been analysed, to remove the contributions of shallow and deep sources to the magnetic anomalies by applying a processing technology that increases the informative potential of the magnetic data acquired by AGIP with great accuracy, uniform distribution and high density. The aeromagnetic anomaly field has been reduced to the bottom topographic surface by the bottom reduction method. Spectral signal analysis has been carried out to separate low- and high-frequency components. The spectral reference field (SRF), obtained from the cotransformation of low frequencies, gives information about deep magnetic structures. The high-frequency components, computed from the difference between the magnetic anomaly field and the SRF, provides the spectral anomaly field (SAF). The bottom reduced magnetic anomaly field is derived by merging the high- and low-frequency bands. The resulting map provides information about geotectonic features in the Southern Tyrrhenian area and shows the effectiveness of the adopted approach over traditional procedures.

Crustal velocity and strain-rate fields in Italy and surrounding regions: new results from the analysis of permanent and non-permanent GPS networks

SUMMARY We present a new geodetic velocity solution for Italy and the surrounding areas, obtained from an analysis of continuous and survey-mode Global Positioning System observations collected between 1991 and 2002. We have combined local, regional and global networks into a common reference frame velocity solution, providing a new detailed picture of the regional-scale deformation field in the central Mediterranean. Our velocity estimates are computed with respect to a new stable Eurasian reference frame, constraining the kinematics of the greater African–Eurasian plate boundary system in the study area. We provide strain-rate values for the main seismotectonic districts, which are in good agreement with the seismic deformation inferred from earthquake focal mechanisms. The southern Tyrrhenian area, Calabria, the Apennines, the southeastern Alps, the southern Dinarides and the Albanides display deformation rates at the order of 20–30 nanostrain yr−1. The Corsica–Sardinia block moves according to Eurasian Plate motions, and there is no indication that the opening of the Tyrrhenian is still active. The Pelagian and Sicilian domains are separated by a northwest–southeast discontinuity, the Sicily Channel rifted area, and marginally significant relative motion between the Pelagian Plateau and the African Plate is also observed. The southern Tyrrhenian is affected by north–south compression and accommodates up to 50 per cent of the Africa–Eurasia relative plate motion, whereas the Calabrian Arc exhibits ∼2 mm yr−1 northwest–southeast extension. The observed deformation pattern suggests the presence of a major approximately north–south tectonic discontinuity separating the Sicilian and Calabrian domains. An extensional boundary observed along peninsular Italy coincides with the distribution of seismogenic faults along the axis of the Apennines. This boundary separates a Tyrrhenian and an Adriatic domain with diverging velocities, orientated north–NNW-ward and northeastward, respectively. The Apennines are extending perpendicularly to the chain axis at rates of less than 3 mm yr−1, and only in the outer northern Apennines indications of active shortening are observed. Insignificant deformation is observed in the western Po Plain and the western Alps, while the central and eastern Alps display north–south shortening. The eastern Adriatic domain is shortening perpendicular to the Dinaric front with strain rates increasing from north to south. The locus of collision between the Aegean/Balkan system and the Adriatic and Ionian domains is marked by the Kephalonia fault system, which accommodates up to 20±1 mm yr−1 of right-lateral motion. The deformation pattern observed in the peri-Adriatic domain is well described by a counter-clockwise rotation of the Adriatic microplate around a pole located in the western Alps.

Geodetic control on recent tectonic movements in the central Mediterranean area

During the Neogene and Quaternary, the western Mediterranean geodynamics was apparently dominated by the nearly eastward migration of the Apenninic arc and the associated opening (spreading) of the back-arc basin (Tyrrhenian Sea). However, during the last 5 My, the collision of the arc with the Apulian platform led to a dramatic change in the tectonic setting of the area. As geological processes require a long period of time to register the displacements of the different blocks, it is indispensable to take into account the present-day motion given by space geodesy data analysis in order to better constrain the geological models. Geodetic motions were derived from Global Positioning System (GPS), Satellite Laser Ranging (SLR) and Very Long Baseline Interferometry (VLBI) observations collected from different networks. All the geodetic solutions have been computed and combined at the Centre of Space Geodesy (CGS), at Matera, Italy. The geodetic results show a NNE motion of the Adriatic plate with a small component of counter-clockwise rotation, in good agreement with the geological and geophysical observations. In the southern Tyrrhenian area, the lengthening of the Matera–Cagliari baseline should imply that convergence cannot be considered as the driving mechanism for the Apenninic subduction process. The estimated motion of Noto is in quite good agreement with the estimated motion of the African plate.

The Seismicity in the Southern Tyrrhenian Area and its Neural Forecasting

—The Southern Tyrrhenian basin is a region characterized by complex tectonics and large-scale geodynamic deformations, and its seismicity has been recently recognized as following fractal laws in its five dimensional set (magnitude, time and space). In particular, the time occurrences of earthquakes are found to follow a significant fractal clustering within the interval ranging from 16 minutes to 24 hours; for longer intervals, the time clustering regime was not significantly different from that of a random process. An artificial neural network is applied here to the same seismicity data set and further evidence of the nonlinear dynamic process, for which the fractal approach failed, is obtained. The monthly values of magnitude predicted by extrapolation are found to be in fair agreement with the historical data.

Experiences of integrated mariculture in a southern Tyrrhenian area (Mediterranean Sea)

To ascertain the potential for exploiting marine areas for mariculture, data on the cultivation of molluscs and fish in the open sea of the southern Tyrrhenian were collected from May 1994 to June 1995. The aims of this integrated study were to test simple breeding methods for molluscs and fish, to apply these to the practices employed by local fishermen and to experiment with the use of a cage system requiring a low level of investment. Crassostrea gigas (Thunberg) and Mytilus galloprovincialis (Lamarck) were cultivated on submerged long lines around cages used for cultivating Seriola dumerili (Risso) and Diplodus puntazzo (Cetti). S. dumerili specimens were placed in two cages and fed with either fish scraps or pellets, while in a third cage, D. puntazzo were fed with pellets only. After a period of 12 months, the following results were obtained: the oysters measured 47.50 ± 12.30 mm and weighed 0.13 ± 0.09 g; the mussels placed in culture as juveniles reached a length of ≈ 40 mm, while the mussels placed in culture as subadults reached the commercial size of about 60 mm. The mean length and weight measurements of the two fish species were as follows: Diplodus 228 ± 14.4 mm and 228 ± 40.48 g; Seriola (lot A) 438.1 ± 25.28 mm and 1149 ± 172.2 g; Seriola (lot B) 347 ± 25.6 mm and 576 ± 139 g.

On the clustering of seismicity in the Southern Tyrrhenian area

High-quality shallow, intermediate and deep shocks from the Southern Tyrrhenian area (interval: 1985-1995) are analysed to draw inferences on the complex shape of the underlying Benioff zone. The hypothesis of an active NW-oriented subduction of the lithosphere, generated and stressed by the opening of the Tyrrhenian basin, is confirmed. The fractal behaviour of seismic data in its five-dimensional set (magnitude, time and space) is significantly identified, even if within specific ranges. The light but significant variations of the different fractal dimensions measured during more recent years is explained in terms of a reduction in the fracturing degree of the Southern Tyrrhenian crust.

The dynamics of back-arc extension: an experimental approach to the opening of the Tyrrhenian Sea

The E-W-opening Tyrrhenian Sea developed after the Cretaceous-Palaeogene Alpine collision, nearly perpendicular to the motion of the African plate, as a back-arc of the Adria-Ionian westward subduction. Three driving mechanisms have been proposed to explain the dynamic evolution of the Tyrrhenian-Apennine system: (1) the northward indentation of the African plate; (2) the retreating subduction of the Adria-Ionian lithosphere; and (3) the gravitational collapse of the Alpine post-collisional wedge. In order to define the relative contribution of each of these mechanisms in the Neogene dynamic of the Tyrrhenian-Apennine system, we performed 3-D laboratory experiments, in which we simulated a retreating subduction process in a compressional regime oriented perpendicularly to the direction of subduction; in this framework we also tested the influence of the gravitational collapse of the overriding plate. Experiments were constructed using dry sand and silicone putties to simulate brittle upper crust and ductile lower crust/upper mantle, respectively; these layers floated on a high-density, low-viscosity glucose syrup which simulated the asthenosphere. The main conclusion of our experiments is that large-scale continental extension, similar to that observed in the Tyrrhenian area, could be reproduced perpendicular to the shortening direction induced by the indentation of the African plate; in this framework, extensional processes are indeed possible if the trench retreat velocity is higher than the rate of shortening induced by the advancing African plate. Our experimental results indicate that this high trench retreat velocity could be explained by the coexistence of the gravitational collapse of the post-Alpine wedge with a slab-pull process, linked to the retreating subduction of the Adria-Ionian plate. While the first mechanism is predominant in the Northern Tyrrhenian area, the second one seems to be important in the latest stage of extension and oceanic accretion of the Southern Tyrrhenian area.

Geodynamic implications of earthquake data in the southern Tyrrhenian sea

Data from short-period seismic stations operating in Calabria, Sicily and the Aeolian Islands have been used to investigate earthquake properties of the southern Tyrrhenian lithosphere. The results have been analyzed, taking into account other geophysical and geological information available in the literature for the same region, with the main purpose of contributing to the definition of local geodynamic processes. Space distribution and focal mechanisms of earthquakes support the hypothesis of southeastward migration of the southern Tyrrhenian lithosphere, shared by several authors in their tectonic modelling of the area. We find that most seismicity appears to be related to two main faults crossing the Aeolian Island archipelago (Sisifo and Vulcano) and propose that these faults are important dislocation structures associated with the lithosphere migration process. We also give a detailed picture of the seismic behaviour of the above-mentioned fault systems by analyzing the earthquake depth distribution, focal mechanisms, seismic clustering and strain release. Some degree of activity was also detected at the eastern boundary of the southern Tyrrhenian area (Calabrian Arc). In particular, our results demonstrate that in this highly stressed zone of contact between different tectonic units (Tyrrhenian and Ionian basins) strain is released under seismic form up to depths of the order of 25 km in the crust and not just in the shallowest structures as proposed by other authors.

Rotation of the Italian peninsula from aeromagnetic evidence

Abstract Palaeomagnetic data have been used extensively in order to study the geodynamical history of a region. Similar information can be obtained by analysing the shape of aeromagnetic anomalies and the direction of the total magnetization vector of the anomaly sources. We can suppose that the direction of the Earth's magnetic induction vector is almost constant with time along a N-S direction. If a significant directional difference between total magnetization and induction vector is observed, we can argue that the anomaly sources were affected by conspicuous rotational movements. In the central Southern Tyrrhenian area, the anomaly shape is generally normal i.e., N-S, except for several anomalies which have a maximum-minimum direction parallel to the Italian coast, that is, NW-SE rather than N-S. This feature, and the location of these anomalies on the border of the bathyal plain, seems to be in agreement with the anticlockwise rotation movements suggested in some geodynamical models of the region.