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Chiarabba C.,Istituto Nazionale di Geofisica and Vulcanologia | de Gori P.,Istituto Nazionale di Geofisica and Vulcanologia | Amato A.,Istituto Nazionale di Geofisica and Vulcanologia
Terra Nova | Year: 2011

Series of multiple main shocks that develop on adjacent faults is a typical way in which active extension is accommodated in the Apennines of Italy. This behaviour is explained by fault interaction that occurs at a scale ranging from seconds to days, yielding a space-time clustering of earthquakes, termed as earthquake storms. We show that the seismic energy released by historical earthquakes in central Apennines is clustered into two main small time periods, around 600 and 300years ago, during which a great portion of the normal faulting belt failed. We favour the hypothesis that clustering results from sudden input of deep fluids into the brittle upper crust. The roughly 300years periodicity and the 3-4mmyear-1 of tectonic extension suggest that earthquake storms need to be taken into account in seismic hazard scenarios. © 2011 Blackwell Publishing Ltd. Source

Chiarabba C.,Istituto Nazionale di Geofisica and Vulcanologia | De Gori P.,Istituto Nazionale di Geofisica and Vulcanologia | Latorre D.,Istituto Nazionale di Geofisica and Vulcanologia | Amato A.,Istituto Nazionale di Geofisica and Vulcanologia
Tectonics | Year: 2014

The Apennines is a mountain belt with paired extension and compression that are explained by the subduction and delamination of the Ionian/Adria lithosphere. During the belt formation, the Adria crust is flexed downward and then incorporated into the wedge after peeling off along some weak level whose origin is still discussed. In southern Apennines, this process seems to have stopped at about 0.7 Ma by the development of a tear in the subducting lithosphere and consequent extension that spread along the mountain range. Seismological data acquired after the 2002 Mw 6.0 Molise strike-slip earthquake yield modeling the structure of the Adria crust as congealed close to the leading edge of the belt. Tomography images show inverted normal faults within the sedimentary cover (Apulian units). Fault inversion, incomplete close to the compressional front, testifies for a final squeezing of the entire, previously flexed, Apulian continental margin. Pronounced high Vp and low Vp/Vs anomalies are observed at depth greater than 12km and undoubtfully attributed to heterogeneities of the basement, solving the long-lasting contention on the nature of similar high-speed bodies observed beneath the Apennines. Beneath these bodies, we observe a strong reflectivity, suggesting the presence of a fluid-filled layer in the middle lower crust that may act as a decoupling level in the Apennines tectonics. The deep fluids are also favoring the rupture of strike-slip earthquakes, like those that occurred in 2002, and the intermediate-depth seismicity diffused in the Apulian region. Key Points We revealed the pristine structure of Adria margin accreted in the Apennines The pristine structure of Adria conditioned the evolution of the belt We document the inversion of normal faults ©2014. American Geophysical Union. All Rights Reserved. Source

Giacomuzzi G.,Istituto Nazionale di Geofisica and Vulcanologia | Civalleri M.,Istituto Nazionale di Geofisica and Vulcanologia | De Gori P.,Istituto Nazionale di Geofisica and Vulcanologia | Chiarabba C.,Istituto Nazionale di Geofisica and Vulcanologia
Earth and Planetary Science Letters | Year: 2012

We compute a high resolution Vs model of the upper mantle underneath Italy by inverting relative residuals of S-wave arrivals from teleseisms recorded at the Italian broad-band national seismic network. We also present a model of Vp/Vs perturbations obtained from similarly resolved P- and S-wave velocity models. The joint analyses of Vs and Vp/Vs models suggests that compositional variations concur with temperature variations to generate the observed velocity patterns, giving deeper insight into the upper mantle structure. The investigation of coherent high Vs and high Vp anomalies permits a comprehensive picture of the main oceanic domains involved in the puzzling subduction system of the central Mediterranean. Slab windows and tears developed in the Ionian slab are highlighted by regions of low Vp, low Vs and high Vp/Vs anomalies. The Adria continental lithosphere is characterized by high Vp, high Vs and low Vp/Vs anomalies that trace the sinking of eclogitized material underneath the Apennines and the Eastern Alps chains. The overall tomographic results yield the development of a new conceptual model for the Alps and Apennines formation, in which three basic processes occurred in different time and different locations all around the Alpine-Apennines system: continental collision, slab break-off and delamination of the upper-plate lithosphere. © 2012 Elsevier B.V. Source

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