Mechanical decoupling along a subduction boundary fault ... 1 1E-01 1E-02 1E-03 1E-04 1E-02 1E-01 1

Mechanical decoupling along a subduction boundary fault ... 1 1E-01 1E-02 1E-03 1E-04 1E-02 1E-01 1

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  • 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 increasing number of studies focused in understanding the lateral terminations of subduction zones. In the Mediterranean region, this topic is of particular interest for the presence of a “land-locked” system of subduction zones interrupted by continental collision and back-arc opening.

    The Tindari-Alfeo Fault System (TAFS) is a major NNW-SSE trending Subduction-Transform Edge Propagator (STEP) that controls the deformation zone bounding the Calabrian subduction zone (central Mediterranean Sea) to the southwest.

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

    The 3D model of the Calabrian subduction was obtained by integrating the shallow subduction interface with the intraslab seismicity distribution that constrains the deep slab geometry.

    Istituto Nazionale di Geofisica e Vulcanologia, Roma

    2 Km

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    WSW ENEInset 1 – section A

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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 the location of section A in the Piacenzian (see Section A inset 1) and the current location 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 obtained from the cumulative vertical offsets measured in section 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-Holocene deposits

    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

    NWSE

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    3 km

    Basins at the front of the accretionary wedge (1) not deformed along the continental margin escarpment (2)

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    STEP 1

    STEP 2

    STEP 3

    STEP 5

    STEP 6

    Strike slip faults

    Normal faults

    Thrust faults

    Deformation bends

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    1E-011E-02 1 1E+01 1E+02 1E+03 1E+04 1E+05 1E+06

    M ax

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    Length (m)

    1. Miocene contractional tectonics (Gallais et al. 2011) 2. Post Messinian growth of the accretionary wedge 3. Interface on the top of U4 propagated after the

    Messinian 4. Duplexing of U3 occurred after the Messinian 5. Major inner thrust controlling the forearc basin

    The seismo-stratigraphic scheme was adopted in order to highlight the structural setting of the Calabrian accretionary wedge 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 dip component of slip rate and propagation rate of the TAFS.

    Length vs Throw compared with literature data

    B o

    n in

    ie t

    al . (

    2 0

    1 6

    ) J

    St ru

    ct G

    eo l

    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 ratio of TAFS segments falls in the range of strike-slip faults at the transition with normal faults.

    References Bonini, 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.2015.03.004 Gallais, Gutscher, Graindorge, Chamot-Rooke, Klaeschen (2011) A Miocene tectonic inversion in the Ionian Sea (central Mediterranean): Evidence from multichannel seismic data. JGR Solid 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 (Central Mediterranean), 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.2004.06.003 Maesano, 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 Confidentiality Agreement (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), Global Bathymetry 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 Software Initiative (ASI) in 2016. This poster benefits from the financial support of the TSUMPAS-NEAM, co-financed by the European Union Civil Protection Mechanism, Agreement Number: ECHO/SUB/2015/718568/PREV26, RITMARE, the INGV Centro per la Pericolosità Sismica (CPS, Seismic Hazard Centre), Porto Empedocle, and PON Massimo Projects.

    The TAFS deformation pattern highlights the presence of mechanical decoupling between the lower plate, constituted by Ionian oceanic crust, and the upper plate, where a thick accretionary wedge has formed. The lower plate hosts the 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 normal faults growing in presence of pre-existing discontinuities (Bonini et al., 2016).

    The deep part of the TAFS shows an increased degree of maturity from from SSE (sections g-h) to NNW (sections b-f). North of the Alfeo Seamount (section a) the TAFS consists of a system of subparallel faults.

    The shallow expression of the TAFS is marked by bending-moment faults and NW-SE elongated basins whose thickness decreases southeastwardly.

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

    Catania

    Siracusa

    …more on Calabrian Arc Accretionary Wedge propagation

    NWSE

    Alfeo Seamount

    Alfeo Seamount

    Alfeo Seamount