The Calabrian Arc subduction complex in the Ionian Sea: Regional architecture, active deformation, and seismic hazard

Abstract

[1] We analyzed the structure and evolution of the external Calabrian Arc (CA) subduction complex through an integrated geophysical approach involving multichannel and single-channel seismic data at different scales. Pre-stack depth migrated crustal-scale seismic profiles have been used to reconstruct the overall geometry of the subduction complex, i.e., depth of the basal detachment, geometry and structural style of different tectonic domains, and location and geometry of major faults. High-resolution multichannel seismic (MCS) and sub-bottom CHIRP profiles acquired in key areas during a recent cruise, as well as multibeam data, integrate deep data and constrain the fine structure of the accretionary wedge as well as the activity of individual fault strands. We identified four main morpho-structural domains in the subduction complex: 1) the post-Messinian accretionary wedge; 2) a slope terrace; 3) the pre-Messinian accretionary wedge and 4) the inner plateau. Variation of structural style and seafloor morphology in these domains are related to different tectonic processes, such as frontal accretion, out-of-sequence thrusting, underplating and complex faulting. The CA subduction complex is segmented longitudinally into two different lobes characterized by different structural style, deformation rates and basal detachment depths. They are delimited by a NW/SE deformation zone that accommodates differential movements of the Calabrian and the Peloritan portions of CA and represent a recent phase of plate re-organization in the central Mediterranean. Although shallow thrust-type seismicity along the CA is lacking, we identified active deformation of the shallowest sedimentary units at the wedge front and in the inner portions of the subduction complex. This implies that subduction could be active but aseismic or with a locked fault plane. On the other hand, if underthrusting of the African plate has stopped recently, active shortening may be accommodated through more distributed deformation. Our findings have consequences on seismic hazard, since we identified tectonic structures likely to have caused large earthquakes in the past and to be the source regions for future events.

Active faults and historical earthquakes in the Messina Straits area (Ionian Sea)

“…In this section we summarize the overall architecture and evolution of the CA subduction complex as derived from an integrated geophysical approach involving the analysis of seismic data at different scales (Polonia et al, 2011). Such architecture and evolution of the CA constitute the structural and geodynamic basis for the present study.…”

“…Shaded relief morpho-bathymetric map compiled using data collected during different cruises by the CIESM/IFREMER Medimap group (Loubrieu et al, 2008). Major faults derived from the tectonic model of Polonia et al (2011) are indicated and labelled STEP, Splay-1, -2, -3, while the thick, discontinuous, NW-SE trending orange lines offshore the Messina Straits represent the boundary between the two lobes, which is marked by a diffuse area of deformation related to scarps, ridges and troughs. Seismic data from the different datasets used in this work are represented by red, blue and green lines.…”

“…Splay-3, in particular, is a major regional tectonic feature, the Calabrian escarpment ( Fig. 1), segmenting across-strike the EL (Polonia et al, 2011). The NE-SW trending Calabria escarpment is the shallow expression of Splay-3, represented at the seafloor by a topographic scarp, where the seafloor deepens to more than 700 m from the rather flat Inner Plateau (average water depth 2000 m) to the intermediate depressions (2800-3000 m water depth).…”

“…The overall geometry of the subduction complex (i.e. depth of the basal detachment, geometry and structural style of different tectonic domains), as well as the location and geometry of major faults, has been reconstructed through an analysis of geophysical data at different scales (Polonia et al, 2011). The complex structure of the subduction complex reflects convergence in a pre-collisional stage, where the African Plate oceanic crust had already been consumed, except in the Ionian Sea abyssal plain.…”

“…The CA subduction complex, in fact, is part of the most active seismic belt of the central Mediterranean region; it faces the highly populated regions of southern Italy, which were struck repeatedly by large magnitude earthquakes in the recent past (Bottari et al, 1989;Jacques et al, 2001;Galli and Bosi, 2003;Gutscher et al, 2006;Jenny et al, 2006), often associated with destructive tsunamis (Piatanesi and Tinti, 1998;Tinti et al, 2004). For several major earthquakes in the region, like the 1908 (Mulargia and Boschi, 1983;Bottari et al, 1986;Capuano et al, 1988;De Natale and Pingue, 1991;Amoruso et al, 2002;Pino et al, 2009) and 1693 (Bianca et al, 1999;Sirovich and Pettenati, 1999;Monaco and Tortorici, 2000;Gutscher et al, 2006), it has Polonia et al (2011). Slip vector in the African reference frame is indicated by a red arrow.…”