Mechanical decoupling along a subduction boundary fault: the case of the Tindari-Alfeo Fault System, Calabrian Arc (central Mediterranean Sea)

Tectonic framework Dataset & interpretation Subduction interface 3D model

Mechanical decoupling Plio-Holocene syn-tectonic basins

In recent years an increasingnumber of studies focused inunderstanding the lateralterminations of subduction zones.In the Mediterranean region, thistopic is of particular interest for thepresence of a “land-locked” systemof subduction zones interrupted bycontinental collision and back-arcopening.

The Tindari-Alfeo Fault System (TAFS) is a major NNW-SSE trendingSubduction-Transform Edge Propagator (STEP) that controls thedeformation zone bounding the Calabrian subduction zone (centralMediterranean Sea) to the southwest.

The 3D reconstruction of the area surrounding the Tindari-AlfeoFault System (TAFS) is based on a dense set of deep seismicreflection profiles, mostly of which provided by Spectrum Geo.

The 3D model of the Calabrian subduction wasobtained by integrating the shallow subductioninterface with the intraslab seismicity distribution thatconstrains the deep slab geometry.

Istituto Nazionale di Geofisica e Vulcanologia, Roma

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1 – Plio-Pleistocene succession

2 – Lower Pliocene pre-TAFS fault succession

3 – Pliocene – Lower Pleistocene (?) syn-TAFS fault turbidites

4 – Pleistocene-Holocene growth strata

5 – Bending moment fault related to deep TAFS fault

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Considering the TAFS has reached thelocation of section A in the Piacenzian(see Section A inset 1) and the currentlocation of its southernmost tip(Gutscher et al., 2017) is ~90 km away,the propagation rate is 24 mm/yr.

The dip component of the slip rate is obtainedfrom the cumulative vertical offsets measured insection A. The reference time is the Piacenzian(first evidence of activity in Section A – inset 1).The resulting rate is 2.2 mm/yr.

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Thickness of Plio-Holocenedeposits

Basins at the front of the accretionary wedge

Elongated basin controlled by TAFS fault

Reference point

Evidence of active tectonics along Plio-Holocene basins related to TAFS fault activity

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Basins at the front of theaccretionary wedge (1) notdeformed along the continentalmargin escarpment (2)

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Strike slip faults

Normal faults

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Deformation bends

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1. Miocene contractional tectonics (Gallais et al. 2011)2. Post Messinian growth of the accretionary wedge3. Interface on the top of U4 propagated after the

Messinian4. Duplexing of U3 occurred after the Messinian5. Major inner thrust controlling the forearc basin

The seismo-stratigraphic scheme was adopted in order tohighlight the structural setting of the Calabrian accretionarywedge and the geometry of the shallow (0-20 km)subduction interface (Maesano et al., 2017).

Dip component of slip rate 2.2 mm/yr

Southeastward propagation of the TAFS 24 mm/yr

Rates averaged over the Piacenzian (3.6 Myr)

TAFS fault tip

There is a factor of 10 between the dipcomponent of slip rate and propagation rate ofthe TAFS.

Length vs Throw compared with literature data

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Francesco E. Maesano, Mara M. Tiberti, Roberto Basili

TAFS fault analysis and propagation rates

Data from Kim and Sanderson (2005) ESR and references therein.

The length/throw ratioof TAFS segments falls inthe range of strike-slipfaults at the transitionwith normal faults.

ReferencesBonini, Basili, Toscani, Burrato, Seno, Valensise (2016) The role of pre-existing discontinuities in the development of extensional faults: An analog modeling perspective. J Struct. Geol.,doi: 10.1016/j.jsg.2015.03.004Gallais, Gutscher, Graindorge, Chamot-Rooke, Klaeschen (2011) A Miocene tectonic inversion in the Ionian Sea (central Mediterranean): Evidence from multichannel seismic data. JGRSolid Earth, doi: 10.1029/2011JB008505.Gutscher et al. (2016) Tectonic expression of an active slab tear from high-resolution seismic and bathymetric data offshore Sicily (Ionian Sea). Tectonics, doi: 10.1002/2015TC003898.Gutscher et al. (2017) Active tectonics of the Calabrian subduction revealed by new multi-beam bathymetric data and high-resolution seismic profiles in the Ionian Sea (CentralMediterranean), EPSL, doi: 10.1016/j.epsl.2016.12.020.Kim and Sanderson (2005) The relationship between displacement and length of faults: a review. ESR doi: 10.1016/j.earscirev.2004.06.003Maesano, Tiberti, Basili (2017) The Calabrian Arc: three-dimensional modelling of the subduction interface. Scientific Reports, doi: 10.1038/s41598-017-09074-8

ORCID 0000-0002-5652-1548 ORCID 0000-0003-2504-853X ORCID 0000-0002-1213-0828

francesco.maesano@ingv.it T31D-0682

Deep fault segments are not connected with shallow faults.

Multichannel seismic reflection surveys in the Ionian sea are kindly provided by Spectrum under a ConfidentialityAgreement (CA-60) with INGV.CROP seismic profiles are provided by CNR-ISMAR.The bathymetric Digital Terrain Model is derived from SRTM30 Plus V6.0 data files. Beckeret al. (2009), GlobalBathymetry and Elevation Data at 30 Arc Seconds Resolution: SRTM30_PLUS, Marine Geodesy, 32:4, 355-371, 2009.Midland Valley Ltd is acknowledged for making available the Move software to INGV under Academic SoftwareInitiative (ASI) in 2016.This poster benefits from the financial support of the TSUMPAS-NEAM, co-financed by the European Union CivilProtection Mechanism, Agreement Number: ECHO/SUB/2015/718568/PREV26, RITMARE, the INGV Centro per laPericolosità Sismica (CPS, Seismic Hazard Centre), Porto Empedocle, and PON Massimo Projects.

The TAFS deformation pattern highlights the presence of mechanicaldecoupling between the lower plate, constituted by Ionian oceanic crust, and theupper plate, where a thick accretionary wedge has formed. The lower plate hoststhe master faults of the TAFS, whereas the upper plate is affected by bending-moment faulting, localized subsidence, stepovers, and restraining/releasing bends.Our observations are supported by analogue modelling experiments of normalfaults growing in presence of pre-existing discontinuities (Bonini et al., 2016).

The deep part of the TAFS shows anincreased degree of maturity fromfrom SSE (sections g-h) to NNW(sections b-f). North of the AlfeoSeamount (section a) the TAFS consistsof a system of subparallel faults.

The shallow expression of the TAFS ismarked by bending-moment faults andNW-SE elongated basins whose thicknessdecreases southeastwardly.

Morpho bathymetricstructural features (in black)from Gutscher et al., (2017)

Catania

Siracusa

…more on Calabrian ArcAccretionary Wedge propagation

NWSE

Alfeo Seamount

Alfeo Seamount

Alfeo Seamount