Recent Activity and Kinematics of the Bounding Faults of the Catanzaro Trough (Central Calabria, Italy): New Morphotectonic, Geodetic and Seismological Data

: A multidisciplinary work integrating structural, geodetic and seismological data was performed in the Catanzaro Trough (central Calabria, Italy) to deﬁne the seismotectonic setting of this area. The Catanzaro Trough is a structural depression transversal to the Calabrian Arc, lying in-between two longitudinal grabens: the Crati Basin to the north and the Mesima Basin to the south. The investigated area experienced some of the strongest historical earthquakes of Italy, whose seismogenic sources are still not well deﬁned. We investigated and mapped the major WSW–ENE to WNW–ESE trending normal-oblique Lamezia-Catanzaro Fault System, bounding to the north the Catanzaro Trough. Morphotectonic data reveal that some fault segments have recently been reactivated since they have displaced upper Pleistocene deposits showing typical geomorphic features associated with active normal fault scarps such as triangular and trapezoidal facets, and displaced alluvial fans. The analysis of instrumental seismicity indicates that some clusters of earthquakes have nucleated on the Lamezia-Catanzaro Fault System. In addition, focal mechanisms indicate the prevalence of left-lateral kinematics on E–W roughly oriented fault plains. GPS data conﬁrm that slow left-lateral motion occurs along this fault system. Minor north-dipping normal faults were also mapped in the southern side of the Catanzaro Trough. They show eroded fault scarps along which weak seismic activity and negligible geodetic motion occur. Our study highlights that the Catanzaro Trough is a poliphased Plio-Quaternary extensional basin developed early as a half-graben in the frame of the tear-faulting occurring at the northern edge of the subducting Ionian slab. In this context, the strike-slip motion contributes to the longitudinal segmentation of the Calabrian Arc. In addition, the high number of seismic events evidenced by the instrumental seismicity, the macroseismic intensity distribution of the historical earthquakes and the scaling laws relating to earthquakes and seismogenic faults support the hypothesis that the Lamezia-Catanzaro Fault System may have been responsible for the historical earthquakes since it is capable of triggering earthquakes with magnitude up to 6.9. possible recent fault activity; (iii) geological structural surveys carried out on the most relevant faults to deﬁne their recent kinematics; (iv) analysis of seismological and geodetic data.


Introduction
The Calabrian Arc (CA hereafter) is an arc-shaped sector of the Apennine-Maghrebian chain structured in the frame of the NW convergence between Eurasia and the Nubia plates [1] (Figure 1A). Since the middle Miocene, this region has been affected by extensional  [17] and Ghisetti [18,19]; TFS is the Tindari Fault System. Inset shows the Alpine-Apenninic-Maghrebian orogen in the context of the Eurasia-Nubia convergence; (B) Geological sketch map of the Central Calabria.  [17] and Ghisetti [18,19]; TFS is the Tindari Fault System. Inset shows the Alpine-Apenninic-Maghrebian orogen in the context of the Eurasia-Nubia convergence; (B) Geological sketch map of the Central Calabria.

The Calabrian Arc
The northwestward subduction of the Ionian lithosphere below the CA was responsible for developing a complex back-arc/forearc/trench system [1]. The presence of distinct lithospheric domains, such as the continental crust of the Pelagian Block (Nubia Plate) and the Apulian Block (Adria Plate), and the oceanic crust of the Ionian Basin between them, has strongly influenced the geodynamic evolution of the subduction system. Due to these crustal heterogeneities, the plates convergence caused (i) diachronous collisional processes at the northern and southern boundaries of the CA [17], where the Apenninic-Maghrebian chain built up, (ii) the formation of an accretionary wedge in the Ionian Sea [20] and (iii) the opening of the back-arc in the Tyrrhenian Basin [21]. Subduction migrated eastward from the Tortonian to Early Pliocene and southeastward from the Late Pliocene to Early Pleistocene [3,4,21,22]. Currently, the subduction of the oceanic crust continues only in a narrow sector between the Tindari Fault System to the south and the Catanzaro Trough to the north [23][24][25][26] (Figure 1A). The southwestern edge of the slab is represented by a NW-SE trending structure classified as a Subduction-Transform Edge Propagator (STEP) highlighted by an abrupt ending of the deep seismicity [25][26][27]. In the northeastern sector, the subduction terminates with a lateral ramp marking the transition from subduction in the CA to collision in the Southern Apennines [24,28].
In the upper crustal sector, the evolution of the CA is controversial. According to Ghisetti and Vezzani [8], the opening of longitudinal grabens and fan-like transverse troughs can be genetically related to the progressive thickening and bowing, respectively, of the CA since the Neogene phase of its SE-ward migration. According to Van Dijk et al. [17], since the Miocene epoch, five major transpressive crustal shear zones, which root into many deep thick-skinned overthrusts, have dissected and deformed the Early Miocene thrust sheet pile. These fault systems caused the structuration of highs and longitudinal and transversal sedimentary basins such as the Catanzaro Trough (see also [2]). Other authors [36][37][38] suggest that these basins developed as a consequence of strike-slip and transtensional tectonics related to different advancements of distinct sectors of the CA. From the middle Pleistocene, contraction was replaced by orogenic extension, which also caused the development of N-S to NE-SW trending normal faults that diffusely offset late Quaternary deposits [2,9,10,39].

The Catanzaro Trough
The Catanzaro Basin is filled by Pliocene-Quaternary sedimentary sequences, consisting of marine and continental deposits, unconformably lying on the CA structural units [47][48][49] (Figure 1B). The CA units encompass Hercynian metamorphic and magmatic rocks, Mesozoic carbonate platform, and middle-late Miocene terrigenous sequences ( [17] and reference therein). The thickness of Pleistocene deposits in the Catanzaro Trough is higher in the northwestern sector. Here, large and widespread alluvial fans [39], likely due to the activity of prevalently normal faults ( Figure 1B) occur. The southern border of the Catanzaro Trough is characterised by on-lapping of Pliocene-Quaternary deposits on crystalline nappes. The top of the sedimentary succession is represented by middleupper Pleistocene marine terraces made up of siliciclastic sands and sandstones, with poor fossiliferous content [39].
The development of the Catanzaro Trough has been controlled by the activity of a primary WNW-ESE to WSW-ENE trending fault system ( Figure 1B), the Lamezia-Catanzaro Fault System, which bound the basin to the north. Two minor north-dipping faults, the Maida Fault and the Stalettì Fault bound the basin to the south [2,39]. The Lamezia-Catanzaro Fault System shows a clear morphologic expression and structural continuity. It is composed of distinct normal/oblique-slip faults, locally arranged in a left-stepping en-echelon pattern (see also [2]). The Lamezia-Catanzaro Fault System shows significant evidence of recent normal faulting in the western sector, where Punzo et al. [50] have recently demonstrated that it is still active but hidden by Holocene deposits. According to Brutto et al. [39], during the late Miocene-early Pliocene, the WNW-ESE trending fault systems were characterised by left-lateral kinematics, switching to right-lateral during the late Pliocene and to extensional kinematics since the middle Pleistocene. This extension, WNW-ESE oriented (see also [10]), has also been accommodated by NE-SW and, subordinately, N-S oriented normal faults producing horst and graben association in the Catanzaro Trough, affecting late Quaternary deposits. Recently, Corradino et al. [51] found evidence of recent activity along NE-SW trending faults in the Sant'Eufemia Gulf that allowed to infer the occurrence of an active~E-W oriented left-lateral transtensional shear zone, extending as far as the Squillace Gulf (Ionian offshore). According to the authors, this likely represents the upper plate response to a tear fault of the lower plate (see also [52]).
During the year 1783, a destructive seismic sequence started on 5 February and lasted until 28 March (maximum Magnitude Mw ≈ 7.1; Io ≈ XI MCS [16]). The last shock of this sequence, which occurred on March 28 (Mw = 7.03 and Imax XI MCS [16]) was located in the central sector of the Catanzaro Trough ( [53]; see composite seismogenic source N. 9 in Figure 3B, from [35]). Although numerous seismotectonic works were undertaken in this area, the epicentral location of this shock is still debated.
On 8 September 1905, a large earthquake (Mw = 7.5 and MCS intensity X-XI [54]) occurred in the western sector of the Catanzaro Trough, likely offshore not far from the coastline [11,55]. This event triggered large landslides accompanied by several cracks, fractures and liquefactions, and generated a tsunami [56] with an estimated height of waves of about 2.5 m [32]. Supported by this evidence, and/or based on marine geophysical data, several authors proposed distinct source models located offshore ( Figure 2B), within the Gulf of S. Eufemia [16,29,57,58]. Recently, among several minor earthquakes, two moderate seismic sequences occurred: 6 July 2017 (Maximum magnitude Mw = 3.7) and October 2019 (maximum magnitude Mw = 4.0) (Figure 2A). During the year 1783, a destructive seismic sequence started on 5 February and lasted until 28 March (maximum Magnitude Mw ≈ 7.1; Io ≈ XI MCS [16]). The last shock of this sequence, which occurred on March 28 (Mw = 7.03 and Imax XI MCS [16]) was located in the central sector of the Catanzaro Trough ( [53]; see composite seismogenic source N. 9 in Figure 3B, from [35]). Although numerous seismotectonic works were undertaken in this area, the epicentral location of this shock is still debated. On 8 September 1905, a large earthquake (Mw = 7.5 and MCS intensity X-XI [54]) occurred in the western sector of the Catanzaro Trough, likely offshore not far from the coastline [11,55]. This event triggered large landslides accompanied by several cracks, fractures and liquefactions, and generated a tsunami [56] with an estimated height of waves of about 2.5 m [32]. Supported by this evidence, and/or based on marine geophysical data, several authors proposed distinct source models located offshore ( Figure 2B), within the Gulf of S. Eufemia [16,29,57,58]. Recently, among several minor earthquakes, two moderate seismic sequences occurred: 6 July 2017 (Maximum magnitude Mw = 3.7) starting point was the use of a high-resolution (5 × 5 m cell size) Digital Elevation Model (DEM) of the study area (Regione Calabrian, http://geoportale.regione.calabria.it/, accessed on 1 September 2021), managed in the GIS software platform (ArcMap 10.2 by ESRI and Global Mapper 20.1). The DEM was integrated with Lidar rendering maps to characterise the faults' geometries. Aerial stereopairs from the Italian Military Geographical Institute (1:33,000 scale) were also analysed. Finally, we performed field surveys on the major faults to check their possible recent activity and define their kinematics ( Figure 4). Structural data were collected at four key measurement stations. Fault surfaces and slickenlines were mapped and analysed using the "FieldMove ® " software. These data were used to determine the geometry and kinematics of major faults and the principal stress orientation.

Methods
Starting from the known regional structural setting, along with the faults reported on available geological maps (Carta Geologica della Calabria, scale 1:25,000), we re-mapped the tectonic structures and analysed the surface features associated to faults. The starting point was the use of a high-resolution (5 × 5 m cell size) Digital Elevation Model (DEM) of the study area (Regione Calabrian, http://geoportale.regione.calabria.it/, accessed on 1 September 2021), managed in the GIS software platform (ArcMap 10.2 by ESRI and Global Mapper 20.1). The DEM was integrated with Lidar rendering maps to characterise the faults' geometries. Aerial stereopairs from the Italian Military Geographical Institute (1:33,000 scale) were also analysed. Finally, we performed field surveys on the major faults to check their possible recent activity and define their kinematics ( Figure 4).
Structural data were collected at four key measurement stations. Fault surfaces and slickenlines were mapped and analysed using the "FieldMove ® " software. These data were used to determine the geometry and kinematics of major faults and the principal stress orientation.

Results
The Lamezia-Catanzaro Fault System (LCFS) extends for a maximum length of~35 km. It is composed of several 10-15 km long segments (Fa, Fb and Fc in Figure 3A) that form a set of steps in the western sector (see also [39]). The southernmost segments (Fa and Fb), which show evidence of recent activity, could be splays of the main fault (Fc) located to the north. These could have been formed when the latter became critically misaligned with the direction of maximum principal stress. Between Lamezia and the Tyrrhenian coastal area ( Figure 3B), these faults displace the upper Pleistocene marine terraces and alluvial fans (conglomerate and sand deposits). Structural data collected mainly in Mesozoic limestones outcropping in the Lamezia area show a prevalence of oblique slickenlines and calcite fibres, indicating a left-lateral component of motion along the WNW-ESE striking fault planes, and prevalent normal kinematics, slightly right-lateral, along the WSW-ENE striking fault planes ( Figure 4A). Morphological evidence, such as the up to 100 m high scarps with triangular and trapezoidal facets in the Pianopoli area ( Figure 4B) and the displaced poly-phased alluvial fans southwest of Lamezia ( Figure 4C), suggests recent normal fault activity along the WNW-ESE trending segments.
On the southeastern border of the Catanzaro Trough, a 300 m high escarpment, juxtaposing crystalline rocks with Pliocene-Middle Pleistocene deposits, characterises the WNW-ESE trending, northeast dipping, Stalettì Fault (SF in Figure 3A). In particular, at the Copanello promontory along the Ionian coast ( Figure 3A), the fault has displaced upper Miocene evaporitic limestones, tilted to the north. Uncertain slickenlines along the coastline suggest oblique normal-left-lateral motion ( Figure 4D). Morphological and structural evidence allowed us to interpret this 6 km long structure (probably extending offshore to the east) as an exhumed fault. The W-E-trending and north-dipping Maida Fault (MF in Figure 3A) is almost 5 km long and, similarly to the Stalettì Fault, shows a deeply eroded escarpment juxtaposing crystalline rocks with Pliocene-Middle Pleistocene deposits. Westwards, it is displaced by the active N-S-oriented Serre Fault ( Figure 3A).
Finally, differential tilting of the middle-late Pleistocene marine terraces allowed us to infer the occurrence of two WSW-ENE trending normal faults below the Holocene deposits of the Amato and Gaccia rivers ( Figure 3A). As also reported by Brutto et al. [39], these faults produced up-faulted and down-faulted blocks inside the Catanzaro Trough (see section A-A' in Figure 3B).

Instrumental Seismicity
Seismological data (magnitude, hypocentral depth and location) of the earthquakes recorded by the INGV National Seismic Network in central Calabria in the last 40 years (see https://istituto.ingv.it/it/risorse-e-servizi/archivi-e-banche-dati.html, accessed on 1 September 2021) were elaborated to create a distribution map of the seismicity and relative sections in depth ( Figure 5). Specifically, in order to improve the quality of the seismic dataset, the events (about 3200, with magnitude mostly in the range 1.0-3.0, with maximum magnitude 4.7) were relocated using a double-difference (DD) algorithm implemented in the tomoDDPS code [59]. The software is able to improve the locations by using a combination of absolute and differential arrival-time readings between couples of closedspaced earthquakes, and by computing the seismic ray-tracing in a 3D velocity model; here we used the model of Scarfì et al. [25], suitable for the Calabrian area. The application of the algorithm produced a better clustering of the seismicity and a significant reduction in the residuals between the observed and theoretical arrival times of about 46%. The final locations are affected by average uncertainties of 0.35 ± 0.25 km in the epicentral coordinates and of 0.52 ± 0.35 km in depth; the average root-mean-square travel-time residual is 0.07 ± 0.03 s. The kinematics of the area ( Figure 6) were analysed through the focal solutions dataset collected by Scarfì et al. [60]. Geosciences 2021, 11, x FOR PEER REVIEW 10 of 20

Data Interpretation
The instrumental seismicity shows a high concentration of events and some clusters mainly in the northern sector of the Catanzaro Trough, in correspondence with the LCFS (see red ellipses in the sections from S7 to S9 of Figure 5), whereas diffuse seismicity characterises the southern sector. To the west, the subducting slab is well depicted by intermediate and deep earthquakes (see red line in the sections from S1 to S4 of Figure 5). In the central sector of the studied area, crustal earthquakes between 10 and 30 km of depth define a roughly N-S alignment (see yellow ellipse in the map of Figure 5).
Among the strongest recorded earthquakes, some are located close to the northern  (Figure 2A). In addition, the mainshock of the seismic sequence that occurred on the 6 July 2017 (Mw = 3.7) was located in the Ionian offshore, close to the Catanzaro coast (Figure 2A).
Focal solutions indicate prevalent left-lateral strike-slip kinematics along the WNW-ESE to ENE-WSW planes of the LCFS, whereas primarily extension on the NNE-SSW to NE-SW fault planes characterises the southwestern and central sectors of the Catanzaro Trough ( Figure 6B). Additionally, it is worth noting that the focal solution of the mainshock of the seismic sequence that recently occurred in this area (7 October 2019; Mw = 4.0) indicates normal kinematics on the NNE-SSW fault planes, some kilometres north of the Caraffa village (Figure 2A).
The P-axis map confirms the change in the direction of the maximum stress axis, from predominantly horizontal in the northern margin of the Catanzaro Trough, along the LCFS, to vertical in the central area ( Figure 6C). The T-axis map ( Figure 6D) shows a predominance of the WNW-ESE oriented extension in the central area of the Catanzaro Trough.

Data Interpretation
The instrumental seismicity shows a high concentration of events and some clusters mainly in the northern sector of the Catanzaro Trough, in correspondence with the LCFS (see red ellipses in the sections from S7 to S9 of Figure 5), whereas diffuse seismicity characterises the southern sector. To the west, the subducting slab is well depicted by intermediate and deep earthquakes (see red line in the sections from S1 to S4 of Figure 5). In the central sector of the studied area, crustal earthquakes between 10 and 30 km of depth define a roughly N-S alignment (see yellow ellipse in the map of Figure 5).
Among the strongest recorded earthquakes, some are located close to the northern  Figure 2A). In addition, the mainshock of the seismic sequence that occurred on the 6 July 2017 (Mw = 3.7) was located in the Ionian offshore, close to the Catanzaro coast (Figure 2A).
Focal solutions indicate prevalent left-lateral strike-slip kinematics along the WNW-ESE to ENE-WSW planes of the LCFS, whereas primarily extension on the NNE-SSW to NE-SW fault planes characterises the southwestern and central sectors of the Catanzaro Trough ( Figure 6B). Additionally, it is worth noting that the focal solution of the mainshock of the seismic sequence that recently occurred in this area (7 October 2019; Mw = 4.0) indicates normal kinematics on the NNE-SSW fault planes, some kilometres north of the Caraffa village (Figure 2A).
The P-axis map confirms the change in the direction of the maximum stress axis, from predominantly horizontal in the northern margin of the Catanzaro Trough, along the LCFS, to vertical in the central area ( Figure 6C). The T-axis map ( Figure 6D) shows a predominance of the WNW-ESE oriented extension in the central area of the Catanzaro Trough.

IGM95-NET GNSS Monitoring
Since 1992 the Italian Istituto Geografico Militare (IGM) (https://www.igmi.org/it/ Home, accessed on 1 September 2021) installed a new geodetic network, currently consist-ing of 2000 benchmarks distributed throughout the Italian territory with an interdistance of about 20 km. This network has also been recently used for scientific purposes in order to calculate the coseismic deformations after the earthquakes of Colfiorito in 1997 [61] and Emilia in 2012 [62], and to estimate the active compression on southwestern Sicily [63] and in eastern Sicily [64].
We have re-surveyed six benchmarks in the Catanzaro Trough area, named as TSGI, CICA, FILA, SQUI, PZCL and SSBR, belonging to the IGM95 network (Figure 7). The benchmarks CICA and SQUI had already been surveyed three times by the IGM; TSGI, PZCL, SSBR were surveyed two times and FILA one time. In 1995, the instruments used by the IGM were Trimble 4000 SSE receivers and Trimble compact with ground plane

Data Interpretation
Considering the tectonic frame, we divided the studied area into four blocks (A, B, C and D) in order to define the kinematics of the major fault zones ( Figure 8B). The GNSS stations located inside each block were grouped in order to calculate the average velocity of each block. This was computed by the weighted average of the velocity of the stations according to their distance to the first-and second-order of regional structures and/or by taking into account if they are located inside a main active transition shear zone ( Figure  8B). After that, we computed the relative velocity of each crustal block with respect to the others, to estimate the kinematics of the main shear zone (Table 1).  Figure 8B) with respect to the others.  To improve the robustness of the network, we added the data of the continuous GNSS station SERS and PLAC, belonging to the RING Network (http://ring.gm.ingv.it/, accessed on 1 September 2021), the data of VIBO, LAM2, CATZ, CTN2, DAVO and MNST belonging to the TopNET live Italy Network (https://rtk.topnetlive.com/italy/networks/ topnet-live-italy, accessed on 1 September 2021) and the processing of the Nevada Geodetic Laboratory (http://geodesy.unr.edu, accessed on 1 September 2021) of AMA1, COM1, LAME, MOS3 and SOV1 (Figure 7). The GNSS data were processed by GipsyX-1.5 [65] using precise ephemerides and clock correction provided by the Jet Propulsion Laboratory (https://sideshow.jpl.nasa.gov, accessed on 1 September 2021). The Earth orientation parameters are from the International Earth Rotation Services (https://www.iers.org, accessed on 1 September 2021). The absolute IGS antenna phase center (GPS week 1958) and the Global Mapping Function (GMF) atmospheric zenith delay models [66] were used to process data. The RINEX (Receiver INdipendent EXchange) files were processed in order to estimate the position of the GNSS stations by the gd2e.py module of GipsyX, which operate in PPP (Precise Point Positioning) mode. For each Day Of the Year (DOY) we obtained covariance matrices that were used to compute the time series tied to the ITRF2014 reference frame [67].

A Fixed
Finally, to show adequately the current deformation field involving the Catanzaro Trough, we subtracted the velocity of eastern Sicily calculated by Carnemolla [68] to the ITRF2014 velocity of the stations. To verify the consistency of the data, we compared our results with those obtained by Palano et al. [69]. They analysed GNSS data from continuous survey stations in south Italy for a period spanning 1994-2011, aligning the horizontal GPS velocity field with respect to a fixed Hyblean-Malta block. We found an average difference of about 0.5-0.8 mm/yr between their and our velocities. Figure 8A shows the horizontal velocities of GNSS stations for the study region, with respect to the Hyblean plateau [69]. Considering the east velocity, we calculated that block A shows velocities of 1.08 and 0.94 mm/yr with respect to blocks B and D, respectively. Considering the north component, we decided to neglect the deformation along this direction due to their low value with respect to their uncertainty. This implies that the Catanzaro Trough is bounded to the north by a shear zone with a prevalent left-lateral component of motion ( Figure 8B) that well matches with the present kinematics of LCFZ (see Sections 3 and 4). Between blocks C and D, we measured an extension of about 1 mm/yr associated to the Serre fault ( Figures 3A and 8B). Finally, we identified the possible prolongation of the Serre fault system in the Catanzaro Trough since a differential motion of 0.14 mm/yr in the east component between the western (block B) and eastern (block D) sectors, separated by a likely blind structure, was measured ( Figures 3A and 8B for the likely location of the inferred fault).

Discussion
Fault mapping, field survey, morpho-structural analysis and seismological/geodetic data allowed defining of the recent kinematics of the major fault system that bounds the Catanzaro Trough. To the north, the WNW-ESE to WSW-ENE-trending, south-dipping Lamezia-Catanzaro Fault System (LCFS) shows evidence of recent normal faulting since it displaces Holocene alluvial fans and shows trapezoidal and triangular facets (see also [39]). Structural analysis suggests that the LCFS has been characterised by normal-oblique left-lateral motion along the WNW-ESE-trending fault planes and normal-oblique rightlateral motion along the WSW-ENE segments ( Figure 4A). Morphotectonic features highlight that the normal component of movement has been prevalent along the WSW-ENE segments ( Figure 4B,C). To the south, the Plio-Quaternary deposits are displaced by minor north-dipping normal faults, Maida Fault and Stalettì Fault, whose activity seems to have run out during late Quaternary times.
The seismological data indicates activity characterised by left-lateral strike-slip kinematics on roughly west-east oriented faults, in correspondence with the LCFS (Figure 6B).

Data Interpretation
Considering the tectonic frame, we divided the studied area into four blocks (A, B, C and D) in order to define the kinematics of the major fault zones ( Figure 8B). The GNSS stations located inside each block were grouped in order to calculate the average velocity of each block. This was computed by the weighted average of the velocity of the stations according to their distance to the first-and second-order of regional structures and/or by taking into account if they are located inside a main active transition shear zone ( Figure 8B). After that, we computed the relative velocity of each crustal block with respect to the others, to estimate the kinematics of the main shear zone (Table 1). Table 1. Relative horizontal velocity of each crustal block (as defined in Figure 8B) with respect to the others. Considering the east velocity, we calculated that block A shows velocities of 1.08 and 0.94 mm/yr with respect to blocks B and D, respectively. Considering the north component, we decided to neglect the deformation along this direction due to their low value with respect to their uncertainty. This implies that the Catanzaro Trough is bounded to the north by a shear zone with a prevalent left-lateral component of motion ( Figure 8B) that well matches with the present kinematics of LCFZ (see Sections 3 and 4). Between blocks C and D, we measured an extension of about 1 mm/yr associated to the Serre fault ( Figures 3A and 8B). Finally, we identified the possible prolongation of the Serre fault system in the Catanzaro Trough since a differential motion of 0.14 mm/yr in the east component between the western (block B) and eastern (block D) sectors, separated by a likely blind structure, was measured ( Figures 3A and 8B for the likely location of the inferred fault).

Discussion
Fault mapping, field survey, morpho-structural analysis and seismological/geodetic data allowed defining of the recent kinematics of the major fault system that bounds the Catanzaro Trough. To the north, the WNW-ESE to WSW-ENE-trending, south-dipping Lamezia-Catanzaro Fault System (LCFS) shows evidence of recent normal faulting since it displaces Holocene alluvial fans and shows trapezoidal and triangular facets (see also [39]). Structural analysis suggests that the LCFS has been characterised by normal-oblique leftlateral motion along the WNW-ESE-trending fault planes and normal-oblique right-lateral motion along the WSW-ENE segments ( Figure 4A). Morphotectonic features highlight that the normal component of movement has been prevalent along the WSW-ENE segments ( Figure 4B,C). To the south, the Plio-Quaternary deposits are displaced by minor northdipping normal faults, Maida Fault and Stalettì Fault, whose activity seems to have run out during late Quaternary times.
The seismological data indicates activity characterised by left-lateral strike-slip kinematics on roughly west-east oriented faults, in correspondence with the LCFS ( Figure 6B). Notable seismic activity, characterised by extension on the NNE-SSW oriented planes, is observed in the central area of the Catanzaro Trough ( Figure 6B), along the band where the WNW-ESE extension is registered between B and D blocks, even though no fault to which the seismicity could be associated outcrops. Seismicity is almost nil in the southern side of the Catanzaro Trough, thus indicating inactivity of the southern bounding faults.
Geodetic data indicate that the crustal block located north of the Catanzaro Trough (A in Figure 8B) moves towards the southeast independently and more slowly with respect to the southern block (B in Figure 8B), and such movement occurs along a belt coinciding with the LCFS; such results confirm the current left-lateral component of movement of this system. Conversely, no relative lateral movement is observed along the faults that bound the Catanzaro Trough to the south. South of the Catanzaro Trough, the WNW-ESE oriented extension is currently accommodated by the N-S oriented Serre Fault (between blocks C and D in Figure 8B). It is worth noting that the WNW-ESE oriented extension also occurs inside the Catanzaro Trough along a band separating the blocks B and D ( Figure 8B), indicating the possibility of a prosecution towards the north of the extension accommodated by the Serre Fault.
Our study confirms that the Plio-Quaternary Catanzaro Trough developed as a poliphased semi-graben (see also [39]) by the activity of the major normal-oblique LCFS that bounds the basin to the north and is still controlling its development. The Maida fault and Stalettì fault that bound the basin to the south appear to be minor faults, no longer active during the Holocene. It is of note that, despite structural and morphological data suggesting a late Quaternary reactivation of the LCFS according to predominantly normal kinematics (see also [2,10,39]), our geodetic and seismological data seem to indicate a current activity characterised by slight left-lateral motion. This is also confirmed by recent faulting in the S. Eufemia Gulf [51].
Considered the current kinematics, the LCFS seems to favour contemporary crustal lateral movements and local extension. Unlike the longitudinal basins of the CA (such as the Mesima and the Crati basins), which are the result of orogenic extension related to isostatic readjustment [8,40], the LCFS could be the upper crustal expression of tearfaulting related to the detachment of the northern boundary of the subducting Ionian slab (see also [52]). According to recent seismological data [25], this slab termination seems to break progressively northwards, parallel to the trench, before being transversally detached ( Figure 9). Moreover, differently from the southern boundary formed by a welldefined STEP fault system [24][25][26][70][71][72], the northern boundary of the subducting Ionian slab is interpreted as a lateral ramp that acts as a gradual transition from subduction in the Calabrian Arc to collision in the Southern Apennines (see also [24,73,74]). Thus, the LCFS transtensional belt should accommodate the lithospheric tear allowing the SE-ward advancement of the CA in the overriding plate ( Figure 9). This strike-slip belt seems to extend westwards in the offshore area of the St. Eufemia Gulf where morphometric and marine geophysical data show recent fault activity [51].
Considered the current kinematics, the LCFS seems to favour contemporary crustal lateral movements and local extension. Unlike the longitudinal basins of the CA (such as the Mesima and the Crati basins), which are the result of orogenic extension related to isostatic readjustment [8,40], the LCFS could be the upper crustal expression of tear-faulting related to the detachment of the northern boundary of the subducting Ionian slab (see also [52]). According to recent seismological data [25], this slab termination seems to break progressively northwards, parallel to the trench, before being transversally detached (Figure 9). Moreover, differently from the southern boundary formed by a well-defined STEP fault system [24][25][26][70][71][72], the northern boundary of the subducting Ionian slab is interpreted as a lateral ramp that acts as a gradual transition from subduction in the Calabrian Arc to collision in the Southern Apennines (see also [24,73,74]). Thus, the LCFS transtensional belt should accommodate the lithospheric tear allowing the SE-ward advancement of the CA in the overriding plate ( Figure 9). This strike-slip belt seems to extend westwards in the offshore area of the St. Eufemia Gulf where morphometric and marine geophysical data show recent fault activity [51].  As a final characterisation of the investigated active faults, we applied fault scaling relationships using fault length and kinematics to estimate the maximum expected magnitude [75,76]. For this purpose, we considered that the LCFS extends for a maximum length of~35 km and it is composed of several 10-15 km long segments (see Section 3.2). Results indicate that the LCFS has a suitable geometrical dimension to generate earthquakes with Mw from 6 to 6.9. The epicentres of 1609, 1626, 1761 and 1821 earthquakes (magnitude between 5.10 and 6.07 [16]) are located in the northern sector of the Catanzaro Trough, at the hanging wall of LCFS (Figure 2A). Similarly, high instrumental seismic activity is observed in correspondence with the LCFS. Thus, considering the magnitude associated with both historical and instrumental earthquakes that occurred in the study area (see Section 2.2), we confirm that the LCFS could represent a possible candidate for the strong seismicity of the Catanzaro Trough region. This fault system well matches with the composite seismogenic source proposed by the DISS Working Group [35], named "Caraffa-Squillace Gulf" ( Figure 2B). As regards the seismic event of 28 March 1783 (Mw = 7.03 and Imax XI MCS [16]), its macroseismic epicentre should be located southwards in the central-eastern sector of the Catanzaro Trough (Figure 2A), making it difficult to attribute this event to the LCFS. However, the location of this event based on macroseismic intensity distribution could be mistaken since it occurred at the end of a disastrous seismic sequence that lasted many months and caused diffuse destruction in southern Calabria. Anyway, our seismological and geodetic data show the likely occurrence of a blind~N-S trending seismogenic source in the central-eastern sector of the Catanzaro Trough (see yellow ellipse of the map in Figure 5), responsible for WNW-ESE extension and intermediate earthquakes.

Conclusions
Our multidisciplinary work, which integrates structural, geodetic and seismological data acquired in the Catanzaro Trough, allows us to draw some conclusions helpful in defining the current geodynamics of the Calabrian Arc:

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The Catanzaro Trough is a semi-graben, developed mainly by the poliphased activity of the LCFS that bounds the basin to the north. The southern faults (i.e., Maida and Stalettì faults) are minor, no longer active, structures that contributed to the crustal deformation. -Geodetic and seismological data reveal that the LCFS and associated structures currently accommodate lateral crustal movements and local extension favouring the SE-ward advancement of the southern sector of the Calabrian Arc. - The LCFS could represent the upper crustal expression of the deep tear-faulting occurring at the northern limit of the transversally detached Ionian slab where the deep transition from subduction to collisional domain occurs. -Given the distribution and the magnitude of both instrumental and historical earthquakes that occurred in the Catanzaro Trough, the LCFS is responsible for the seismicity of this region. Considering its geometry and kinematics, the LCFS is capable of generating earthquakes with a magnitude up to 7.1. - The geodetic and seismological data highlight the occurrence of the WNW-ESE oriented extension inside the Catanzaro Trough, allowing the inference of the presence of a NNE-SSW oriented blind fault (northern prosecution of the Serre Fault) that concur with the present seismicity of the area and could have been responsible for historical events. Future research could highlight the field evidence of this inferred structure by performing paleo-seismological investigations through trench excavation.