Enrico Serpelloni

Mantle dynamics in the Mediterranean

The Mediterranean offers a unique opportunity to study the driving forces of tectonic deformation within a complex mobile belt. Lithospheric dynamics are affected by slab rollback and collision of two large, slowly moving plates, forcing fragments of continental and oceanic lithosphere to interact. This paper reviews the rich and growing set of constraints from geological reconstructions, geodetic data, and crustal and upper mantle heterogeneity imaged by structural seismology. We proceed to discuss a conceptual and quantitative framework for the causes of surface deformation. Exploring existing and newly developed tectonic and numerical geodynamic models, we illustrate the role of mantle convection on surface geology. A coherent picture emerges which can be outlined by two, almost symmetric, upper mantle convection cells. The downwellings are found in the center of the Mediterranean and are associated with the descent of the Tyrrhenian and the Hellenic slabs. During plate convergence, these slabs migrated backward with respect to the Eurasian upper plate, inducing a return flow of the asthenosphere from the backarc regions towards the subduction zones. This flow can be found at large distance from the subduction zones, and is at present expressed in two upwellings beneath Anatolia and eastern Iberia. This convection system provides an explanation for the general pattern of seismic anisotropy in the Mediterranean, first-order Anatolia and Adria microplate kinematics, and may contribute to the high elevation of scarcely deformed areas such as Anatolia and Eastern Iberia. More generally, the Mediterranean is an illustration of how upper mantle, small-scale convection leads to intraplate deformation and complex plate boundary reconfiguration at the westernmost terminus of the Tethyan collision.

Vertical GPS ground motion rates in the Euro‐Mediterranean region: New evidence of velocity gradients at different spatial scales along the Nubia‐Eurasia plate boundary

We use 2.5 to 14 years long position time series from >800 continuous Global Positioning System (GPS) stations to study vertical deformation rates in the Euro-Mediterranean region. We estimate and remove common mode errors in position time series using a principal component analysis, obtaining a significant gain in the signal-to-noise ratio of the displacements data. Following the results of a maximum likelihood estimation analysis, which gives a mean spectral index ~ −0.7, we adopt a power law + white noise stochastic model in estimating the final vertical rates and find 95% of the velocities within ±2 mm/yr, with uncertainties from filtered time series ~40% smaller than from the unfiltered ones. We highlight the presence of statistically significant velocity gradients where the stations density is higher. We find undulations of the vertical velocity field at different spatial scales both in tectonically active regions, like eastern Alps, Apennines, and eastern Mediterranean, and in regions characterized by a low or negligible tectonic activity, like central Iberia and western Alps. A correlation between smooth vertical velocities and topographic features is apparent in many sectors of the study area. Glacial isostatic adjustment and weathering processes do not completely explain the measured rates, and a combination of active tectonics and deep-seated geodynamic processes must be invoked. Excluding areas where localized processes are likely, or where subduction processes may be active, mantle dynamics is the most likely process, but regional mantle modeling is required for a better understanding.

Convergence vs. retreat in Southern Tyrrhenian Sea: Insights from kinematics

[1] The Tyrrhenian Sea is an extensional basin opened by trench retreat and back-arc extension during subduction of the Calabrian slab in the last 10-12 My. Subduction is still active beneath the SEmost part of the Tyrrhenian Sea, as testified by seismicity down to 500 km depth. By analyzing seismicity and geodetic data, together with recent tomographic images, we define the present-day situation. An evident ∼N-S compressional regime prevails in the Tyrrhenian region west of the Aeolian archipelago, while east of them a NNW-SSE extension is documented by focal mechanisms and GPS data, with a much smaller strain rate with respect to the past. The transition between these two domains is accommodated by a N-S discontinuity zone which runs from Aeolian Islands to Mt. Etna with an extensional to strike-slip deformation.

Coastal structure, sea-level changes and vertical motion of the land in the Mediterranean

Abstract The Mediterranean basin is an important area of the Earth for studying the interplay between geodynamic processes and landscape evolution affected by tectonic, glacio-hydro-isostatic and eustatic factors. We focus on determining vertical deformations and relative sea-level change of the coastal zone utilizing geological, archaeological, historical and instrumental data, and modelling. For deformation determinations on recent decadal to centennial time scales, seismic strain analysis based on about 6000 focal mechanisms, surface deformation analysis based on some 850 continuous GPS stations, and 57 tide gauge records were used. Utilizing data from tectonically stable areas, reference surfaces were established to separate tectonic and climate (eustatic) signals throughout the basin for the last 20 000 years. Predominant Holocene subsidence (west coast of Italy, northern Adriatic sea, most of Greece and Turkey are areas at risk of flooding owing to relative sea-level rise), uplift (local areas in southwestern Italy and southern Greece) or stability (northwestern and central western Mediterranean and Levant area) were determined. Superimposed on the long trends, the coasts are also impacted by sudden extreme events such as recurring large storms and numerous, but unpredictable tsunamis caused by the high seismicity of parts of the basins. Supplementary material: A table of locations and timings of the largest tsunamis in the Mediterranean during the last 5660 years BP is available at http://www.geolsoc.org.uk/SUP18757.

Creep and locking of a low-angle normal fault: Insights from the Altotiberina fault in the Northern Apennines (Italy)

While low-angle normal faults have been recognized worldwide from geological studies, whether these structures are active or capable of generating big earthquakes is still debated. We provide new constraints on the role and modes of the Altotiberina fault (ATF) in accommodating extension in the Northern Apennines. We model GPS velocities to study block kinematics, faults slip rates and interseismic coupling of the ATF, which is active and accounts, with its antithetic fault, for a large part of the observed chain normal 3 mm/yr tectonic extension. A wide portion of the ATF creeps at the long-term slip rate (1.7 ± 0.3 mm/yr), but the shallow locked portions are compatible with M > 6.5 earthquakes. We suggest that positive stress accumulation due to ATF creep is most likely released by more favorable oriented splay faults, whose rupture may propagate downdip along low-angle normal fault surface and reduce the probability of occurrence of a seismic rupture of the shallower locked portion.

The coseismic and postseismic deformation of the L’Aquila, 2009 earthquake from repeated GPS measurements

We analyze more than 100 GPS time series of continuous and discontinuous GPS stations located in the Abruzzi region (Italy) surrounding the epicentres of the L’Aquila 2009 seismic sequence. The purpose of this work is to reconstruct the coseismic displacement field caused by the 6 th April (Mw 6.3) main shock from a dense network of survey-mode stations surrounding the epicentral area and to characterize the early postseismic deformation field. In the months following the main shock, an extensive GPS survey was carried out on the existing Central Apennines Geodetic Network (CAGeoNet), with the intention of collecting a robust data set and to study the co- and postseismic deformation field of this Apenninic normal faulting earthquake. The analysis is carried out with two independent procedures and software (Bernese and Gamit) in order to provide reliable and validated geodetic solutions. The analysis of the postseismic transients and the knowledge of long-term inter-seismic velocities at all GPS stations, issued from permanent and CAGeoNet sites, allow us to derive a dense co- and postseismic displacement field for the L’Aquila Mw 6.3 main shock in a wide area around the epicentre. The highest deformation rate occurs during the first 4–5 months after the main shock and persists in the following at slightly slower rate throughout the whole monitoring period. Fast deformation rates imply that most of the observed deformation is due to a process different from a pure viscoelastic relaxation of the stress perturbation. Since the observed rates would imply a too low effective viscosity value (below 10 17 Pa s), we rather suggest that most of the observed deformation in the first months after the earthquake is due to different processes, most likely frictional afterslip possibly modulated by the presence of fluids. The new coseismic displacement field is used to invert for the main shock fault geometry, analysing the consistency among the different geodetic solutions and the combined one, with the goal of validating the two data sets.

Constraining primary surface rupture length along the Paganica fault (2009 L’Aquila earthquake) with geological and geodetic (DInSAR and GPS) data

Part of this work has been carried out within the ASI-SIGRIS project, funded by the Italian Space Agency and Istituto Nazionale di Geofisica e Vulcanologia

Aseismic deformation associated with an earthquake swarm in the northern Apennines (Italy)

Analyzing the displacement time series from continuous GPS (cGPS) with an Independent Component Analysis, we detect a transient deformation signal that correlates both in space and time with a seismic swarm activity (maximum M_w=3.69 ± 0.09) occurred in the hanging wall of the Altotiberina normal fault (Northern Apennines, Italy) in 2013–2014. The geodetic transient lasted ∼6 months and produced a NW-SE trending extension of ∼5.3 mm, consistent with the regional tectonic regime. The seismicity and the geodetic signal are consistent with slip on two splay faults in the Altotiberina fault (ATF) hanging wall. Comparing the seismic moment associated with the geodetic transient and the seismic events, we observe that seismicity accounts for only a fraction of the measured geodetic deformation. The combined seismic and aseismic slip decreased the Coulomb stress on the locked shallow portion of the ATF, while the transition region to the creeping section has been loaded.

Flooding scenario for four Italian coastal plains using three relative sea level rise models

ABSTRACT The coastal areas of the central Mediterranean Sea are sensitive to climate change and the consequent relative sea level rise. Both phenomena may affect densely urbanized and populated areas, causing severe damages. Our maps show the land-marine flooding projections as effects of the expected relative sea level rise for four Italian coastal plains using (i) IPCC AR5 estimations, based on the IPCC RCP 8.5 emission scenarios and (ii) the Rahmstorf 2007 model. Isostatic and tectonic data were added to the global projections to estimate the relative sea changes expected along the coastline by 2100, as well as sea-flooding. The northern Adriatic map shows the study area, extending for about 5500 km2, and is presented at a scale of 1:300,000 with two inset maps at a scale of 1:150,000. The Oristano coastal plain is about 125 km2; the map scale is at 1:60,000 with an inset map scale at 1:33,000. The Cagliari coastal study area extends for 61 km2; the map scale is at 1:60,000 with two inset maps at 1:30,000. The Taranto area extends for 4.2 km2 and is represented at a scale map of 1:30,000, while the three inset maps are at a scale of 1:10,000.

Application and analysis of geodetic protocols for monitoring subsidence phenomena along on-shore hydrocarbon reservoirs

Abstract In this study, we tested the “land-subsidence monitoring guidelines” proposed by the Italian Ministry of Economic Development (MISE), to study ground deformations along on-shore hydrocarbon reservoirs. We propose protocols that include the joint use of Global Positioning System (GPS) and multi-temporal Differential Interferometric Synthetic Aperture Radar (DInSAR) techniques, for a twofold purpose: a) monitoring land subsidence phenomena along selected areas after defining the background of ground deformations; b) analyzing possible relationships between hydrocarbon exploitation and anomalous deformation patterns. Experimental results, gathered along the Ravenna coastline (northern Italy) and in the southeastern Sicily (southern Italy), show wide areas of subsidence mainly related to natural and anthropogenic processes. Moreover, ground deformations retrieved through multi-temporal DInSAR time series exhibit low sensitivity as well as poor spatial and temporal correlation with hydrocarbon exploitation activities. Results allow evaluating the advantages and limitations of proposed protocols, to improve the techniques and security standards established by MISE guidelines for monitoring on-shore hydrocarbon reservoirs.