Active Tectonics of the North Tunisian Continental Margin

1. Introduction The study area of the North Tunisian continental margin encompass the diffuse boundary between the Nubia and Eurasian plates (Figure1). The region is currently in a contractional tectonic setting driven by the NW–SE plate convergence regime (e.g., Camafort etal.,2020; Serpelloni etal.,2007). The neighboring northern Algeria and northern Sicily that are comparatively better studied, currently display abundant seismicity, concordant with a compressional regime (e.g., Billi etal.,2011; Bougrine etal.,2019; Hollenstein etal.,2003; Meghraoui & Doumaz,1996; Nocquet,2012; Serpelloni etal.,2007; Stich etal.,2006; Totaro etal.,2016) (Figure1). Offshore north Tunisia, the lack of seismicity and scarce seismic profiling information has prevented a detailed tectonic study. Here, we present a structural analysis of the active tectonics in the north Tunisian continental margin. The main goal is to integrate bathymetric maps with parametric echosounder images in order to study the shallow structure of the area and to identify active tectonic structures, and determine fault style and kinematics. The result is the integration of high-resolution TOPAS profiles and high-resolution bathymetry as a fault map with unprecedented detail for the region. 2. Methodology To characterize the offshore active tectonics, we integrated 2D parametric echosounder profiles, acquired with the Kongsberg TOPAS PS 18 sub-bottom profiler installed on-board the research vessel (RV) “Ángeles Alvariño.” High-resolution bathymetry was acquired with the ELAC Seabeam 1050D on the RV “García del Cid” and the Kongsberg EM710 multibeam echosounders on the RV “Ángeles Alvariño.” The data sets were acquired during the Geomargen-2 and Geomargen-2AA cruises in 2013. Multibeam sounds were systematically cleaned using Teledyne CARIS software and converted to depth using Vp/depth profiles daily collected during the two cruises. The high-resolution seafloor maps were composed by approximately 30m grid node spacing, locally reaching up to approximately 10m node spacing in the shallower regions. The survey region covers an area of approximately 15,600km 2 between longitude 9°3.6′ and 11°16.6′E, and latitude 37°14.7′ and 38°41.2′N in a Abstract A poorly defined boundary between the Nubia and Eurasian plates runs along the Northern Tunisian continental margin. The Tunisia margin is deformed by a slow NW–SE trending convergence resulting in a diffuse deformation zone with scarce and scattered seismicity compared to the seismic activity into the neighboring regions to the east and west along the boundary. The area has been poorly studied and therefore its recent evolution is almost unknown, particularly offshore. Here, we present a structural analysis of the active tectonics in this submarine continental margin. The data used for this analysis are high-resolution bathymetric maps together with parametric echosounder images which have allowed to obtain a map of active faulting with unprecedented detail. The structural analysis supports a dominantly transpressive to compressive component of faulting, resulting from the current regional NW–SE trending compressive regime between plates. The North-eastern Domain of the study region contains the highest number of active faults with numerous pockmarks aligned along them. This study shows that the plate boundary across the North Tunisia margin is incipient and poorly developed, which may be due to the fact that deformation is partitioned over a large number of structures, each accommodating a small percentage of convergence, with the exception of the Hayat fault system. The Hayat reverse fault, striking WSW–ENE, is the largest fault system that comparatively may accommodate a greater amount of displacement, and is probably responsible for the uplift of the North-eastern Domain of the continental margin. CAMAFORT ET AL. © 2022. The Authors. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. Active Tectonics of the North Tunisian Continental Margin Miquel Camafort1 , César R. Ranero1,2 , and Eulàlia Gràcia1 1Barcelona Center for Subsurface Imaging, Institut de Ciències del Mar - CSIC, Barcelona, Spain, 2ICREA, Passeig de Lluís Companys 23, Barcelona, Spain Key Points: • We present the structural analysis of the active tectonics in the north Tunisian continental margin • Faulting shows a dominantly transpressive to compressive component, resulting from the current regional NW–SE compressive regime • Fault distribution is unequal across the margin with the largest density in the North-eastern Domain associated to the Hayat reverse fault Correspondence to: M. Camafort, camafor[email protected] Citation: Camafort, M., Ranero, C. R., & Gràcia, E. (2022). Active tectonics of the North Tunisian continental margin. Tectonics, 41, e2021TC007110. https://doi. org/10.1029/2021TC007110 Received 27 OCT 2021 Accepted 19 MAR 2022 Author Contributions: Investigation: Miquel Camafort, César R. Ranero Writing – original draft: Miquel Camafort Writing – review & editing: César R. Ranero, Eulàlia Gràcia 10.1029/2021TC007110 RESEARCH ARTICLE 1 of 20 Tectonics CAMAFORT ET AL. 10.1029/2021TC007110 2 of 20 range from 18 to 2,221m depth. More than 3.500km of TOPAS 2D profiles were used in this work that were collected mainly in the Eastern and North-eastern Domains (Figure2), which contain the largest number of active faults indicated by the bathymetric relief. 2.1. Criteria for Fault Classification In order to create a systematic classification of the fault systems we defined four different groups on the basis of their seismic and bathymetric expression (Table1): 1. Possible faults are interpreted only from geomorphologic structures because either there are not TOPAS data or seismic images do not provide valid information (e.g., regions of low TOPAS penetration). 2. Inferred faults are interpreted from coincident geomorphologic and seismic structures. Although fault offsets have not been imaged, indirect witnesses such as strata geometry (e.g., either growth strata or tilted strata) in TOPAS profiles supports recent and ongoing tectonic activity. 3. Blind faults show offsets imaged in seismic data and associated geomorphologic relief, but the fault plane does not reach the seafloor. These faults cut strata in the TOPAS images that are Quaternary and younger than approximately 1,725 kyr (lower Calabrian). Although there is a debate on the length of the time past since the last slip event occurred that is used to define active faults, it is commonly accepted that a given fault is considered potentially active if it slipped during the Quaternary (e.g., Keller & Pinter,2002). Although the beginning of the Quaternary has been re-defined to 2.58Ma (ICS,2018) opening the question of the time interval to use, we interpret that the blind faults mapped in our data can be interpreted as active faults because they moved more recently than approximately 1.7Ma. Blind fault traces are displayed in yellow in our maps and in the TOPAS profiles. In the maps, faults are classified as “main” and “secondary” depending on their dimensions. 4. Surface rupture faults are defined by both, morphological and seismic evidences. They cut the seafloor and the strata imaged on TOPAS profiles. These faults have been active during the Holocene (past 10 kyr), and are always considered active faults (Keller & Pinter,2002). Surface ruptures in our maps and faults on TOPAS images are displayed in red color. The faults are classified as “main” and “secondary” depending on their dimensions. In addition, recent folding in the study region is classified by its dimensions as “main” folds or “secondary” folds. 3. Tectonic Domains Based on mapped active tectonic structures we defined three main tectonic domains (Figure2): Figure 1. Focal mechanism solutions for all ≥Mw3.9 event from the Global CMT catalog for the period between 1976 and 1996 (Global CMT,2015) and the RCMT catalog between 1997 and 2015 (RCMT,2015). Horizontal velocities (with 95% error ellipses) given with respect to the Eurasian plate (after Serpelloni etal.,2007) along the Nubia-Eurasia boundary in western Mediterranean. The yellow polygon delineates the study area. Ust, Ustica island. Tectonics CAMAFORT ET AL. 10.1029/2021TC007110 3 of 20 1. The North-eastern Domain is bounded to the west by the Bizerte Canyon and to the south by the southern flank of the Bizerte Ridge. 2. The Eastern Domain covers the area east of the Bizerte Canyon, bounded to the north by the Bizerte Ridge. 3. The Western Domain which covers the area west of the Bizerte Canyon. Next, we describe each of the tectonic domains. 3.1. The North-Eastern Domain In the North-eastern Domain, bathymetry depicts elongated troughs with numerous pockmarks aligned along them. The troughs are the surface expression of fault traces that appear to have played a role controlling the up-flow migration of gas-rich fluids and consequently, the generation and preservation of pockmarks. In the North-eastern Domain fault traces average trend is N25°–N30°, and fault-associated folds are subparallel to the fault traces, and therefore their axes follow the same trend (Figures3 and4). In addition to the N25°–N30° main trend, some minor faults trend at N15°– N25° and N30°–N40° (Figures3 and4). The faults delineate a series of basin with fault-influenced deposition (Camafort, Gràcia, & Ranero,2020). Figure 2. Bathymetric map of the North Tunisian continental margin. The main tectonic domains are bounded by the three white polygons. TOPAS tracks are thin black lines and are mainly located on the North-eastern and Eastern domains. Fault classification Bathymetric evidence TOPAS evidence Do not cut strata Cut strata Cut surface Possible fault Inferred fault Blind fault Main Secondary Surface rupture fault Main Secondary Note. Classification criteria is the same for strike-slip, normal or thrust fault and the type, when interpreted, is indicated with symbols in the maps of Figures 4, 12, 17 and 18. Table 1 Fault Classification Criteria Applied in Our Work Tectonics CAMAFORT ET AL. 10.1029/2021TC007110 4 of 20 Fault mapping and seafloor relief delineate left-lateral pull-apart basins throughout the North-eastern Domain (Figures3–5). The fault named Angioletta displays steep fault planes that cut the seafloor, which supports that it is currently active. The pull-apart basin geometry in map view indicates a left-lateral strike-slip fault motion (Figures3 and4), supported by TOPAS images (Figure5b and5c). North and south of the pull-apart basin (Figure5a and5d), the Angioletta fault changes its relative displacement from reverse to normal. This along-strike change, from normal to reverse slip, is also observed in other strike-slip faults in the area. Several NNW-SSE trending en-echelon traces observed within the North-eastern Domain, display oblique sinistral strike-slip faulting (Figures3 and4). The sinistral component agrees with the regional stresses inferred from the NW–SE convergence between the Nubia and Eurasia plates on this sector at the south-western extension of the Tyrrhenian Sea. A rose diagram of fault strike shows that the approximately N30°W convergence vector is oblique to the main N25°E–N30°E faults (Figure4). Pure normal and reverse faults also occur in the North-eastern Domain (Figure5b and5c). The normal SE-dipping fault of Figure5b and5c cuts the seafloor, supporting recent activity. Mass transport deposits (MTDs) imaged on the hanging-wall of the normal fault, may have resulted from co-seismic shaking (Camafort, Gràcia, & Ranero,2020). This kind of structure-less deposits and slide scars, are common features in the North-eastern Domain. A SE-dipping reverse fault named Amalia, folds and uplifts the seafloor and has syn-tectonic deposits thickening toward the east, which together with onlap terminations toward the west indicate the uplift of the western flank (Figure6). The Amalia-fault shows slide-scars on the western flank and structure-less facies on the footwall, which affect the most recent strata (Figure6a and6b). These features suggest recent sliding, likely resulting from slip of the Amalia fault, which further supports recent activity. Pure normal and reverse fault slip-distribution also agrees with convergence stresses in the region. Reverse faults predominantly trend ENE–WSW, striking near-perpendicular to the main convergence vector (Figure4). Normal faults mainly trend NNE–SSW, being highly oblique to the convergence vector (Figure4). Figure 3. The north-eastern tectonic domain. (a) Colored-shaded relief bathymetric map. (b) Zoom of the area showing the pull-apart basin of the Angioletta fault and the Amalia reverse fault. Location of TOPAS profiles is depicted by dashed black lines (Figures5–10). Tectonics CAMAFORT ET AL. 10.1029/2021TC007110 5 of 20 Faults in the southernmost sector trend about N25°–N30° and cross the Bizerte Ridge (Figures3 and4). The main faults crossing the Bizerte Ridge do not cut the shallowest strata, indicating that they may be secondary to deeper faults or have not been recently active (Figure7). The seafloor deformation supports that some deep faults are active (e.g., reverse fault at offset approximately 12,500 in Figure7b). The main faults appear associated to troughs in the bathymetry, where steep walls of fault-scars prevent TOPAS imaging the termination of strata (i.e., main faults in Figure7). The fault traces extend toward the north and south along a smooth seafloor, supporting that they also run along the troughs. The steepness of the faults indicates a predominant strike-slip motion, as in the northernmost areas. Comparatively, fewer reverse and normal faults occur. In general, fault trends are similar to faults in the north, with strike-slip faults changing along-strike the slip component. The Bizerte Ridge is probably the surface expression of an anticline fold, formed above a Sto SE-directed thrust. Seismic reflection profiles show that the region of the north Tunisian margin is underlaid by a Sto SE-directed imbricated fold and thrust-belt system formed during the early-middle Miocene (Tricart etal.,1994). The Bizerte Ridge may be associated to a recently reactivated fault perhaps of the original set of thrusts. The Bizerte Ridge south-eastern flank displays onlap terminations and pinch-out geometries of the youngest layers indicative of contemporaneous uplift, supporting recent/ongoing fault activity (Camafort, Gràcia, & Ranero,2020). Tilted strata likely corresponds to the forelimb of the fold creating the Bizerte ridge (Figure8). This structural configuration supports a S-verging thrust-fault under the south-east flank of the Bizerte Ridge, that we name Hayat fault. The Hayat fault appears a regional reverse blind-thrust that likely caused the uplift of the northern sector of the study region, possibly related to a highly orthogonal fault trend to the current NW–SE convergence (Figure4). It is 23km long within the studied area and extends further toward the east. We do not have seismic images out from our area of study, so we can only speculate that it extends some more 20–30km as the associated Bizerte Ridge seems to indicate. Figure 4. Recent tectonic framework of the North-eastern Domain (faults and folds). The rose diagram shows the average orientation of the North-eastern Domain faults clustered in 5° groups. The white arrow shows the GPS horizontal velocity of the closer permanent station, MILO in western Sicily (Serpelloni etal.,2007), relative to the Eurasian plate. The absolute kinematic rate in MILO station is 3.5±0.6mm/yr with an orientation of approximately N30°W. Main fault systems are labeled. Location of the TOPAS profiles across the fault systems is depicted by aligned black dots (Figures5–10). Tectonics CAMAFORT ET AL. 10.1029/2021TC007110 6 of 20 Figure 5. TOPAS profiles showing the pull-apart basin of the Angioletta fault (a, b, c, and d). Faults with seafloor rupture are represented in red color, while blind faults are shown in yellow. Location is shown in Figures3 and4. Tectonics CAMAFORT ET AL. 10.1029/2021TC007110 7 of 20 The depression next to the Bizerte Ridge shows slide scars, transparent sediment packages and tilted blocks indicative of MTDs (Figure8). These features likely relate to uplift of the Bizerte Ridge, and may also be related to minor reverse N-verging faults (Figure 8a). Fault-related structures are more significant toward the east (Figure8a), indicating that the Hayat fault grows toward the west (Figure8b). Using the margin seismo-stratigraphy (Camafort, Gràcia, & Ranero,2020) and assuming that the noncontourite strata were deposited fundamentally Figure 6. Three parallel TOPAS profiles showing the Amalia active reverse fault (in red). Blind faults are shown in yellow color. Line location is depicted in Figures3 and4. Tectonics CAMAFORT ET AL. 10.1029/2021TC007110 8 of 20 with a subhorizontal attitude, the current layering geometry supports an uplift-rate estimated as approximately 0.24mm/yr for the last 471 kyr, due to slip on the Hayat reverse fault. Assuming a 45° dip for the Hayat fault, this uplift-rate would correspond to 0.33mm/yr slip-rate during the last 471 kyr. This value is estimated from the strata geometrical relationship imaged on Figure8a, thus in the western sector of the fault, where the offset is smaller than in the eastern segment, so that the slip-rate might be larger there. Another important active feature in the North-eastern Domain corresponds to a fault system that bounds the basin H to the west (Figures3 and4). This system, with a NE–SW orientation, extends from the Sentinelle Valley in the north through the Bizerte Ridge in the south (Figures3 and4). The main fault of this system, named Valeria, cuts the seafloor and generates a wide fold, supporting recent activity (Figure9). Seafloor morphology above the subvertical Valeria fault supports that the fold is a pressure ridge formed by the interaction of Valeria fault with secondary faults. The Valeria fault possibly dips slightly toward the east, and sediment layers thinning toward the fold indicate reverse slip on the fault (Figure9). The activity of this fault-system in the northern and southern sectors is obscured by rougher topography, which makes difficult to determine recent activity and slip-component (e.g., faults in Figure7). The S-shaped morphologies along the fault corridor (Figures3 and4) may indicate a sinistral strike-slip system, with changes in slip along-strike indicated by locally reverse-slip (e.g., Figure9). Numerous faults follow a similar NE–SW main regional trend along Cornaglia slope (i.e., to the south and north in Figures3 and4). The detailed trace of the faults is not evident due to slide scars carving the slope seafloor. These scars display a trend following the main NE-SW faulting, which supports that slides initiate along the trace of faults. A profile along the strike of the south Cornaglia slope displays comparatively little faulting, several slide scars and a smooth strata geometry, where a few subvertical fault planes with small vertical offset, cut the seafloor, and indicate strike-slip fault kinematics (Figure10). 3.2. The Eastern Domain The seafloor of the Eastern Domain displays few active fault traces in comparison to the North-eastern Domain. The fault lineaments associated to elongated troughs containing pockmarks described in the North-eastern Domain have no clear continuation toward the south. Similarly, tectonic structures imaged by TOPAS profiles are comparatively subdued. Few recently active tectonic structures are recognized throughout the Eastern Domain, mainly following the regional NE–SW dominant trend. Figure 7. TOPAS profiles showing Blind and Inferred faults (in yellow and white, respectively) across the Bizerte Ridge (Valeria fault is depicted in a). Location is shown in Figures3 and4. Tectonics CAMAFORT ET AL. 10.1029/2021TC007110 9 of 20 The Valeria fault system is the most significant tectonic feature, extending into the northernmost sector of the Eastern Domain. This fault corridor changes from a NE–SW orientation to a N–S trend, delineating an S-shaped bathymetric-high, that we name Snake Ridge (Figures11 and12). A significant normal fault together with conjugated faults and transparent deposits, possibly representing MTDs, and tilted strata, occur on the hanging-wall to the main fault, corresponding to the eastern flank of the high (Figure13a and13b). The MTDs support recent sudden slip of faults, although are covered by a thin undisturbed sediment veneer, indicating some elapsed time since the last fault slip causing sliding, or that the fault has not slip since approximately 146 kyr (age derived from the seismostatigraphy; Camafort, Gràcia, & Ranero,2020). Toward the south-west, the fault corridor may link to or dissect the Resgui Bank (Figures11 and12). Although the structure of the connection is not clear on the TOPAS images, seafloor relief supports a structural continuity. The S-shaped topographic high relief of the north-eastern sector of the Resgui Bank is similar to the NE–SW trending Snake Ridge, which have been described above with supporting fault control (Figures11 and12). The fault corridor continues south of the Resgui Bank, where MTDs along a NE–SW trending confined depression seems to be related to a NE–SW trending significant fault-activity (Figure13c and13d). However, the images do not show offset strata, so that we classify them as inferred faults. The sinuous shape of the corridor within the Eastern Domain indicates a sinistral strike-slip component, similar to structures of the North-eastern Domain. Figure 8. TOPAS profiles showing the southeastern boundary of the Hayat fault-related features. The Hayat blind-fault and other blind-faults are represented in yellow color. (a) Onlap geometries, tilted blocks, anticline, slide-scars, and chaotic facies. (b) Transparent facies are mass transport deposits (MTDs) located near slide scars. Line location is shown in Figures3 and4. Ages of the horizons are taken from Camafort, Gràcia, and Ranero(2020). Tectonics CAMAFORT ET AL. 10.1029/2021TC007110 16 of 20 display pure NE–SW reverse kinematics and NNE–SSW back-thrusts concordant with the regional stress field. In contrast, basin B shows strike-slip faults and west-dipping reverse faults that uplift the eastern basin edge. Minor faults at the head of the Bizerte canyon might be related to the major fault underlying Bizerte Canyon, which may currently have a sinistral strike-slip component, matching the current N30°W contractional regime. In contrast to the North-eastern Domain where faulting generally dip toward the E or SE, the Eastern Domain contains E or SE dipping faults and opposite NW dipping faults (i.e., basins F and B). The relief map supports that the NE-SW trending faults of the North-eastern Domain extend north of our high resolution map, into the Tyrrhenian Basin (Figure18). Faults trending NE–SW and dipping preferentially toward the south-east have been imaged on deep-penetrating seismic images along the south-western region of the Tyrrhenian, across the north Sicily Margin (Figure19; Guzman,2015; Prada etal.,2016). These faults form horsts and grabens associated to the opening of the Tyrrhenian Basin. North of our study area, these faults dip eastward, indicating that the shallow SE-dipping active faults, identified in the North-eastern Domain and northern sector of the Eastern Domain, might be extensional faults formed during Tyrrhenian opening (Loreto etal.,2020; Prada etal.,2020) about approximately 8–6Ma (Mascle & Rehault,1990; Trincardi & Zitellini,1987). These previously normal faults are currently being inverted on a transpressional system in the frame of the present NW–SE convergence between the Nubia and Eurasian plates (Figure4). Undifferentiated Plio-Quaternary minor phases of inversion and recent compressive folding have been described along the edge of the Tunisian plateau in the Figure 17. Interpreted shaded relief map of the Western Tectonic Domain. Framework of the recent tectonic structures in the Western tectonic Domain. Tectonics CAMAFORT ET AL. 10.1029/2021TC007110 17 of 20 Figure 18. Recent tectonics of the North Tunisian continental margin. Epicenters of magnitude Mb between 3 and 6 are from the International Seismological Centre (ISC,2018). The main tectonic domains are bounded by the three white polygons. Dashed black line depicts the boundary between Algeria and Tunisia. SF: Samia fault, HF: Hayat fault, VF: Valeria fault, BCF: Bizerte Canyon fault. Figure 19. Interpreted multichannel seismic (MCS) profile across the North Sicily margin taken from Guzman(2015). Recent faults and seismo-stratigraphic sequence, from Pleistocene to Tortonian are depicted. Inset: Colored bathymetric map of the North Tunisian Margin with the location of the MCS profile in a black line (SAR, Sardinia; SIC, Sicily; TUN, Tunisia). Tectonics CAMAFORT ET AL. 10.1029/2021TC007110 18 of 20 Sardinia Channel area (Mascle etal.,2001,2004; Tricart etal.,1990,1994) and is active in the Tyrrhenian Basin (Sulli etal.,2021; Zitellini etal.,2020). The south Tyrrhenian active contractional belt trending E–W north of Sicily (i.e., to the east of the North-eastern Domain, Figure18) is inferred to be segmented by a succession of ENE–WSW and NE–SW trending reverse faults, and NW–SE right-lateral strikeand oblique-slip faults (Billi etal.,2007). Based on focal mechanisms, the ENEto NE-striking faults are proposed to be high-angle south verging reactivated inherited faults (Billi etal.,2007). The Hayat fault (Figure18), along the south-eastern flank of the Bizerte Ridge, displays a pattern that supports reactivation of an inherited NW-dipping fault. Thus, the ongoing convergence between Nubia and Eurasia, possibly reactivates either transtensional or transpressional strike-slip faults that originally were generated during the opening of the Tyrrhenian Basin (i.e., SE-dipping, NE-SW trending faults of the North-eastern Domain). Likewise, the NW-dipping NE–SW trending faults of the North-eastern and Eastern domains may correspond to the reactivation of older faults from the fold-and-thrust belt system, formed in the African margin during the opening of the Algero-Balearic Basin at approximately 17–14Ma. The estimated approximately 0.33mm/yr slip-rate for the Hayat fault during the last 471 kyr is significantly larger than the slip of any other NE–SW reverse fault, all with smaller offsets, of the North-eastern Domain. The highly orthogonal attitude of the Hayat fault with respect to the Nubia-Eurasia convergence vector and strongly tilted strata at the forelimb of the Bizerte Ridge, suggests that Hayat fault is likely a major fault accommodating much of the convergence between the plates on the studied area (Figure4). Furthermore, slip on the Hayat fault appears to control the topographic evolution of the northern sector, and is responsible of its uplift (Camafort, Gràcia, & Ranero,2020). Several seismo-tectonic and geodetic studies propose that the current approximately 5mm/yr convergence between the Nubia and Eurasian plates in the central Mediterranean is currently being completely or largely absorbed across the southern Tyrrhenian seismic belt (Figure1) (Billi etal.,2011; Goes etal.,2004; Nocquet,2012; Serpelloni etal.,2007; Totaro etal.,2016). Along Algeria, the current approximately 2–3mm/yr of convergence are accommodated in a narrow belt along the north-Algerian margin (Figure1; e.g., Bougrine etal.,2019; Meghraoui & Doumaz,1996; Serpelloni etal.,2007; Stich etal.,2006). In our study area, it appears that a considerable amount of the total convergence is being accommodated by the Hayat fault, although we have not being able to calculate its cumulative strain. However, the region to the east of our survey area displays poorly quantified deformation that has some seismicity associated (Figure18) and may contain unmapped active tectonic structures. Serpelloni etal.(2007) noted that the residual shortening of the 2.3±0.5mm/yr NW-ward drift of Sicily has to be accommodated between Ustica (in NW Sicily) and the Corsica-Sardinia block, that is, N-NE of our study region. Due to the lack of instrumental seismic events along this region, Serpelloni etal.(2007) suggest that compression is probably transferred northwards, in Liguria, where active thrusting has been described (e.g., Bigot-Cormier etal.,2004; Larroque etal.,2001). Although some convergence might be absorbed in Liguria, our study supports that part of the shortening is accommodated within our study region, mainly by the Hayat fault and across the North-eastern Domain sinistral fault system. The main NE-SW trending sinistral strike-slip system in a transpressive regime defined in our study area differs from the faulting in northern Sicily and Algeria. There, both areas display compressional regimes with prevailing thrust focal mechanisms (e.g., Billi etal.,2011; Serpelloni etal.,2007). 5. Conclusions The structural analysis of high-resolution seafloor maps and TOPAS images reveals for the first time multiple active fault systems defined in the in the north Tunisian continental margin. The tectonic structures display variable expressions in the data which has led to a classification in four groups based on their characteristics that refers to the certainty on their presence and in their current activity. Surface Rupture Faults display both morphological and seismic features and offset to the seafloor. They are active during the Holocene (0.1Ma) and considered currently active faults. Blind Faults offset strata at depth and have associated seafloor relief, but they do not cut the seafloor. They cut strata younger than approximately 1,725 kyr (lower Calabrian) and can be considered active faults. Inferred faults involve seafloor morphologic and seismic structures. Faults do not offset strata in images but their geometry (e.g., growth strata or tilted strata) supports recent tectonic activity. Possible faults are interpreted from seafloor relief structures because either we do not have profiles or the imaging is poor. Tectonics CAMAFORT ET AL. 10.1029/2021TC007110 19 of 20 The North Tunisia continental margin fault systems dominantly show a transpressive to compressive component, resulting from the current NW–SE plate convergence compressive regime. Based on the density and significance of active tectonic structures, we defined three main tectonic domains. The North-eastern Domain is located in the transition from the Tyrrhenian basin to the North Tunisia margin, and it is bounded to the west by the Bizerte Canyon and to the south by the southern flank of the Bizerte Ridge. The North-eastern Domain contains the highest number of active faults, the largest and longest fault systems, and the greatest fault-associated relief. The largest fault systems form lineaments that contain numerous pockmarks along them, possibly related to recent fluid expulsion. The largest fault systems form sigmoidal seafloor highs containing uplifted consolidated sediment. Further south, extends the Eastern Domain, covering the area east of the Bizerte Canyon and bounded to the north by the Bizerte Ridge, and to the south by the narrow continental shelf. A few fault systems extend from the north into this domain, although fault density decreases abruptly. The Western Domain covers the area west of the Bizerte Canyon, which contains only few seafloor morphologies that may indicate recent faulting, while most of it displays a dominantly smooth seafloor. Most surface rupture and blind faults (i.e., active faults) occur within the North-eastern Domain. These faults are mainly SE-dipping NE–SW trending faults, possibly originally formed during the opening of the Tyrrhenian Basin segment to the north at approximately 8–6Ma. Currently, they are reactivated with strike-slip displacement and inverted in compression due to plate convergence. The kinematic indicators of the faults of the North-eastern Domain support a transpressional regime with a main sinistral strike-slip faulting style. Faults dipping NW and trending NE–SW are related to the older fold-thrust belt system, formed during the early-middle Miocene, during the opening of the Algero-Balearic basin. Some of these faults are also reactivated with different fault kinematics, such as reverse faults in basin B and normal faults in basin F. The largest fault system is the WSW-ENE Hayat reverse fault, located south of the Bizerte Ridge. This structure is likely accommodating much of the plate convergence within the studied area. The recent slip of Hayat fault appears also responsible for the uplift of the North-eastern Domain. Thus, the plate boundary deformation across the North Tunisia margin is incipient and partitioned over a large number of structures, each accommodating a comparatively small percentage of convergence, with the exception of the Hayat fault system that, relatively, may accommodate a larger amount of displacement. This broad zone of deformation may also explain the lack of instrumental seismicity in the study area. Some of the deformation might be occurring to the East of our study area yet undetected in the poorly studied East Tunisia continental margin. 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