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 back-arc regions toward 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.

Seismic precursors are an as yet unattained frontier in earthquake studies. With the aim of making a step towards this frontier, we present a hydrogeochemical dataset associated with the 2016 Amatrice-Norcia seismic sequence (central Apennines, Italy), developed from August 24th, with an Mw 6.0 event, and culminating on October 30th, with an Mw 6.5 mainshock. The seismic sequence occurred during a seasonal depletion of hydrostructures, and the four strongest earthquakes (Mw ≥ 5.5) generated an abrupt uplift of the water level, recorded up to 100 km away from the mainshock area. Monitoring a set of selected springs in the central Apennines, a few hydrogeochemical anomalies were observed months before the onset of the seismic swarm, including a variation of pH values and an increase of As, V, and Fe concentrations. Cr concentrations increased immediately after the onset of the seismic sequence. On November 2016, these elements recovered to their usual low concentrations. We interpret these geochemical anomalies as reliable seismic precursors for a dilational tectonic setting.

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The Tindari Fault System (southern Tyrrhenian Sea, Italy) is a regional zone of brittle deformation located at the transition between ongoing contractional and extensional crustal compartments and lying above the western edge of a narrow subducting slab. Onshore structural data, an offshore seismic reflection profile, and earthquake data are analyzed to constrain the present geometry of the Tindari Fault System and its tectonic evolution since Neogene, including the present seismicity. Results show that this zone of deformation consists of a broad NNW trending system of faults including sets of right‐lateral, left‐lateral, and extensional faults as well as early strike‐slip faults reworked under late extension. Earthquakes and other neotectonic data provide evidence that the Tindari Fault System is still active in the central and northern sectors and mostly accommodates extensional or right‐lateral transtensional displacements on a diffuse array of faults. From these data, a multiphase tectonic history is inferred, including an early phase as a right‐lateral strike‐slip fault and a late extensional reworking under the influence of the subduction‐related processes, which have led to the formation of the Tyrrhenian back‐arc basin. Within the present, regional, geodynamic context, the Tindari Fault System is interpreted as an ongoing accommodation zone between the adjacent contractional and extensional crustal compartments, these tectonic compartments relating to the complex processes of plate convergence occurring in the region. The Tindari Fault System might also be included in an incipient, oblique‐extensional, transfer zone linking the ongoing contractional belts in the Calabrian‐Ionian and southern Tyrrhenian compartments.

seismic slip in the geological record. However, pseudotachylytes form at >5 km depth, and there are many rock types in which they do not form at all. We performed low- to high-velocity rock friction experiments designed to impose realistic coseismic slip pulses on calcite fault gouges, and report that localized dynamic recrystallization may be an easy-to-recognize microstructural indicator of seismic slip in shallow, otherwise brittle fault zones. Calcite gouges with starting grain size <250 μm were confi ned up to 26 MPa normal stress using a purpose-built sample holder. Slip velocities were between 0.01 and 3.4 m s−1, and total displacements between 1 and 4 m. At coseismic slip velocities ≥0.1 m s−1, the gouges were cut by refl ective principal slip surfaces lined by polygonal grains <1 μm in size. The principal slip surfaces were fl anked by <300 μm thick layers of dynamically recrystallized calcite (grain size 1–10 μm) containing well-defi ned shape- and crystallographic-preferred orientations. Dynamic recrystallization was accompanied by fault weakening and thermal decomposition of calcite to CO2 + CaO. The recrystallized calcite aggregates resemble those found along the principal slip surface of the Garam thrust, South Korea, exhumed from <5 km depth. We suggest that intense frictional heating along the experimental and natural principal slip surfaces resulted in localized dynamic recrystallization, a microstructure that may be diagnostic of seismic slip in the shallow crust

""Calabria represents an ideal site to analyze the. topography of a subduction zone as it is located on. top of a narrow active Wadati‐Benioff zone and shows. evidence of rapid uplift. We analyzed a pattern of surface. deformation using elevation data with different. filters and showed the existence of a long wavelength. (>100 km) relatively positive topographic signal at the. slab edges. The elevation of MIS 5.5 stage marine. terraces supports this pattern, although the record is. incomplete and partly masked by the variable denudation. rate. We performed structural analyses along. the major active or recently reactivated normal faults. showing that the extensional direction varies along the. Calabrian Arc and laterally switches from arc‐normal,. within the active portion of the slab, to arc‐oblique or. even arc‐parallel, along the northern and southern slab. edges. This surface deformation pattern was compared. with a recent high resolution P wave tomographic. model showing that the high seismic velocity anomaly. is continuous only within the active Wadati‐Benioff. zone, whereas the northern and southwestern sides are. marked by low velocity anomalies, suggesting that. large‐scale topographic bulges, volcanism, and uplift. could have been produced by mantle upwelling. We. present numerical simulations to visualize the threedimensional. mantle circulation around a narrow retreating. slab, ideally similar to the one presently subducting. beneath Calabria. We emphasize that mantle upwelling. and surface deformation are expected at the edges of. the slab, where return flows may eventually drive decompression. melting and the Mount Etna volcanism."

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