Geometry of the deep Calabrian subduction (Central Mediterranean Sea) from wide‐angle seismic data and 3‐D gravity modeling

Type Article
Date 2020-03
Language English
Author(s) Dellong David1, 2, Klingelhoefer FraukeORCID1, Dannowski Anke3, Kopp Heidrun3, 4, Murphy ShaneORCID1, Graindorge David2, Margheriti Lucia5, Moretti Milena5, Barreca Giovanni6, Scarfì Luciano7, Polonia Alina8, Gutscher Marc-Andre2
Affiliation(s) 1 : Géosciences Marines, IFREMER, Centre de Brest Plouzané , France
2 : UMR LGO, University of Western Brittany Brest , France
3 : GEOMAR , Kiel , Germany
4 : Christian Albrechts, University Kiel , Germany
5 : Istituto Nazionale di Geofisica e Vulcanologia (INGV), Centro Nazionale Terremoti Rome, Italy
6 : Dipartimento di Scienze Biologiche, Geologiche ed Ambientali, University of Catania Catania, Italy
7 : Istituto Nazionale di Geofisica e Vulcanologia (INGV), Osservatorio Etneo Catania,Italy
8 : ISMAR CNR, Bologna, Italy
Source Geochemistry Geophysics Geosystems (1525-2027) (American Geophysical Union (AGU)), 2020-03 , Vol. 21 , N. 3 , P. 23p.
DOI 10.1029/2019GC008586
Keyword(s) Ionian Basin, wide-angle seismic, gravity, crustal structure, seismicity, tomography

The Calabrian subduction zone is one of the narrowest arcs on Earth and a key area to understand the geodynamic evolution of the Mediterranean and other marginal seas. Here in the Ionian Sea, the African plate subducts beneath Eurasia. Imaging the boundary between the downgoing slab and the upper plate along the Calabrian subduction zone is important for assessing the potential of the subduction zone to generate mega‐thrust earthquakes and was the main objective of this study. Here we present and analyze the results from a 380 km long, wide‐angle seismic profile spanning the complete subduction zone, from the deep Ionian Basin and the accretionary wedge to NE Sicily, with additional constraints offered by 3‐D Gravity modeling and the analysis of earthquake hypocenters. The velocity model for the wide‐angle seismic profile images thin oceanic crust throughout the basin. The Calabrian backstop extends underneath the accretionary wedge to about 100 km SE of the coast. The seismic model was extended in depth using earthquake hypocenters. The combined results indicate that the slab dip increases abruptly from 2‐3° to 60‐70° over a distance of ≤50 km underneath the Calabrian backstop. This abrupt steepening is likely related to the roll‐back geodynamic evolution of the narrow Calabrian slab which shows great similarity to the shallow and deep geometry of the Gibraltar slab.

Plain language abstract

We investigate the deep crustal structure of southern Italy and the Central Mediterranean where some of the oldest oceanic crust on Earth is actively descending (subducting) into the earth's interior (Speranza et al., 2012). This process causes much of the moderate seismicity observed in this region and may be responsible for strong historical earthquakes as well (Gutscher et al., 2006). Deep seismic data recorded during a marine geophysical expedition performed in 2014, allow us to reconstruct the 3‐D geometry of this subduction zone. Our data reveal a 1‐4 km thick evaporitic (salt bearing) layer in the 13 km thick accretionary wedge. The thin underlying crust has characteristics of oceanic crust. The adjacent onshore domains (E Sicily and SW Calabria) are composed of 25‐30 km thick crust with velocities typical of continental crust. Together with earthquake travel‐time tomography (providing images of the subducting slab down to 300 km) and gravity modeling we can for the first time image the abrupt steepening of the subducting slab, the “slab hinge”, where slab dip increases from ≤5° to >60° over a downdip distance of 50 km. This slab dip is steep compared to other subduction zones, for example in Northern Honshu Japan or Sumatra, where the slab dip remains roughly 10° down to 40 km depth and therefore may have consequences on the seismicity of the region.

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Figure S4 79 KB Open access
Figure S5 7 MB Open access
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Dellong David, Klingelhoefer Frauke, Dannowski Anke, Kopp Heidrun, Murphy Shane, Graindorge David, Margheriti Lucia, Moretti Milena, Barreca Giovanni, Scarfì Luciano, Polonia Alina, Gutscher Marc-Andre (2020). Geometry of the deep Calabrian subduction (Central Mediterranean Sea) from wide‐angle seismic data and 3‐D gravity modeling. Geochemistry Geophysics Geosystems, 21(3), 23p. Publisher's official version : , Open Access version :