Preprints
https://doi.org/10.5194/egusphere-2025-3844
https://doi.org/10.5194/egusphere-2025-3844
18 Sep 2025
 | 18 Sep 2025
Status: this preprint is open for discussion and under review for Solid Earth (SE).

First Tomographic Imaging of Mid-Crustal Doubling at the Abruzzi Outer Thrust Front, Central-Southern Italy

Rita de Nardis, Donato Talone, Luca De Siena, Maria Adelaide Romano, Francesco Brozzetti, and Giusy Lavecchia

Abstract. The geometry, deep structural style, and seismotectonic setting of the outer Abruzzi thrust system are less understood than those of other segments of Italy's Late Pliocene–Quaternary contractional belt. This knowledge gap arises from the region's complex surface geology, low seismicity rates, and the limited resolution of existing geophysical data.

Here, we present a local earthquake tomography of a large and previously unexplored area that encompasses the Abruzzi thrust system and spans from the Apennine extensional province in the west to the foreland strike-slip province in the east. The model is based on the inversion of 42,176 P-wave and 29,045 S-wave arrival times from earthquakes with ML ranging from 0.2 to 5.5.

Our results show low seismic velocities at upper crustal levels in the western sectors, correlating with continental basins of the extensional domain. In contrast, marked Vp inversions at mid- to lower-crustal depths in the eastern sector delineate a crustal doubling.

We interpret the tomographic results in the context of geological, geophysical, and seismological data to construct a 3D conceptual model of the region. This includes the first geometric reconstruction of the Abruzzi Arc basal thrust, an eastward convex arcuate structure extending ~170 km and reaching depths of ~24 km. The model also incorporates strike-slip faults in the footwall and east-dipping normal faults to the west.

The structural affinity between the Abruzzi Arc basal thrust and other seismogenic structures of the Padan–Adriatic belt located in the same structural position, suggests potential seismogenic behavior, although slow deformation rates and long recurrence intervals obscure its seismic expression. This conceptual model provides new insights into regional geodynamics and has significant implications for seismic hazard assessment in the central–southern Apennine transition zone.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
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Rita de Nardis, Donato Talone, Luca De Siena, Maria Adelaide Romano, Francesco Brozzetti, and Giusy Lavecchia

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Rita de Nardis, Donato Talone, Luca De Siena, Maria Adelaide Romano, Francesco Brozzetti, and Giusy Lavecchia
Rita de Nardis, Donato Talone, Luca De Siena, Maria Adelaide Romano, Francesco Brozzetti, and Giusy Lavecchia

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Short summary
The Outer Thrust System (OTS) in coastal Abruzzi (Italy) remains debated in terms of its geometry, seismic activity, and deformation style. This study presents a new seismic tomography of the Abruzzi Arc basal thrust, revealing mid-crustal doubling at depths of 14–24 km. The conceptual 3D model highlights deep compressive tectonics influencing the crustal structure. If the thrust is seismogenic, it could have significant implications for regional geodynamics and seismic hazard assessment.
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