Dipartimento di Scienze Biologiche, Geologiche e Ambientali, Sezione di Scienze della Terra, Università di Catania, Italy 2

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1 Structural pattern and active deformation in the northern sector of the Aeolian-Tindari-Letojanni fault system in the geodynamic framework of the southern Calabrian Arc: an integrated analysis of field, marine geophysical, seismological and geodetic data G. Barreca 1,7, F. Cultrera 1, L. Ferranti 2,7, C. Monaco 1,7, F. Pepe 3, S. Passaro 4, G. Barberi 5, V. Bruno 5, P. Burrato 6, M. Mattia 5, C. Musumeci 5, L. Scarfì 5 1 Dipartimento di Scienze Biologiche, Geologiche e Ambientali, Sezione di Scienze della Terra, Università di Catania, Italy 2 Dipartimento di Scienze della Terra, delle Risorse e dell Ambiente, Università Federico II, Napoli, Italy 3 Dipartimento di Scienze della Terra e del Mare, Università di Palermo, Italy 4 Istituto per l Ambiente Marino Costiero, C.N.R., Napoli, Italy 5 Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio etneo, Catania, Italy 6 Istituto Nazionale di Geofisica e Vulcanologia, Roma 1, Roma, Italy 7 CRUST - Centro Interuniversitario per l Analisi Sismotettonica Tridimensionale con Applicazioni Territoriali, Italy Framed in the current geodynamics of the central Mediterranean, the Aeolian-Tindari- Letojanni fault system (ATLFS) represents a key tectonic feature controlling volcanism and seismicity of southern Tyrrhenian Sea and north-eastern Sicily (Fig. 1A). Although it is widely accepted that the ATLFS is part of a wider NW-SE oriented right-lateral wrench zone developed at the southern edge of the Calabrian Arc, several issues about its structural pattern, active deformation processes and related seismogenic faulting are still unsolved. These aspects are of crucial importance is assessing its seismogenic potential considering that, as provided by seismological, geodetic and geological data (Billi et al., 2006; Palano et al., 2012; Barreca et al., 2014; Scarfì et al., 2016), ATLFS is still active heaving produced about 2000 earthquakes with small-to-moderate magnitude (1.0 Ml 4.8) in the last 30 years. Moreover, the analysis of historical catalogues revealed that this area was also affected by several strong earthquakes in the past such as the Mw=6.2 event in March 1786 and the Mw=6.1 one in April 1978, which caused severe damages in the surrounding localities (Gasparini et al., 1982; Rovida et al., 2011). In order to investigate the structural architecture and the active deformation pattern of the northern sector of this deformation belt, structural observations on-land, high and very-high resolution seismic reflection profiles, swath bathymetry and seismological and geodetic data were merged from the Lipari-Vulcano volcanic complex to the Peloritani Mountains across the Gulf of Patti (Fig. 1B). As a whole, structural measurements were performed along the on-land sectors of the faults belt (i.e. Lipari-Vulcano complex and Tindari-Barcellona Depression, Fig. 1B) and highlight how the zone is mainly deformed by right-lateral transtensional faults along the NNW-SSE direction. Minor faults, cinematically linked to the previous, consist of NE-SW to NNE-SSW trending normal to oblique faults. In mainland Sicily, the main set is represented by a NW-SE to NNW-SSE trending right-oblique (transtensional) fault zone which extends for ~20 km from Capo Tindari to Novara village (Tindari-Novara fault zone, TNFZ). The offshore sector (i.e. between Vulcano Island and the Gulf of Patti) was investigated through marine geophysical survey during which high (sparker) and very-high (Chirp) resolution seismic reflection profiles and about 1100 km² of swath bathymetry were acquired. The combined analysis of these data point out that oblique NW-SE striking faults are widespread all over the offshore sector often forming horst and graben structural associations and controlling the main morpho-bathymetric features (e.g. the Milazzo Canyon and the Patti Valley, Fig. 2A). Overall, offshore geophysical surveys allow detecting two major oblique structural lineaments oriented NW-SE, the Vulcano-Milazzo fault zone (VMFZ) and the Patti Valley fault zone (PVFZ). Further, chirp profiles revealed that some of the detected fault segments reach the seafloor producing up to 3 m-high scarps. By merging the results coming from the on-land and marine investigations on a new structural map, a more complete structural framework of the whole area was obtained (Fig. 2B). Major 108

2 Fig. 1 - A) The Aeolian-Tindari-Letojanni Fault System (ATLFS) is a regional deformation belt extending from the central sector of the Aeolian Archipelago to the eastern coast of Sicily and separating two active tectonic compartments: a contractional one to the west and an extensional one to the north-east. In its north-western portion, the ATLFS system connects with the eastern branches of the Sisifo-Aliἀcudi transpressional fault belt (SAFS). The yellow stars represent the location of the Mw=6.2, 1786 and Mw=6.1, 1978 earthquakes. B) Multidisciplinary dataset considered in this study. Data conἀsist of field-based structural analyses carried out along the Lipari-Vulcano complex and the Peloritani Mts. (80 sites of measurements), high- and very-high resolution seismic profiles (~500 km) and swath bathymetry data (1000 km²) acquired in the Gulf of Patti, seismological (from 1999 to 2015) and geodetic (from 1996 to 2008) measurements. 109

3 Fig. 2 - A) 3D view of the Sparkἀer profile SP 19 which, in its central sector, shows horst and graben structures that dislocate Holocene deposits whereas in the eastern sector display a horst structure affecting the offshore of the Capo Milazzo peninsula. B) Structural map of the Gulf of Patti obtained by picking fault segments on the whole seismic dataset.detected faults mainly consist of extensional (or transtensional) structures arranged into two azimuthal (NW SE and N S trending) domains. 110

4 Fig. 3 - A) Map view of the final seismic events location and selectἀed fault plane solutions (lowἀer-hemisphere projection). Locaἀtion of the main faults detected in the area was also reported (VMFZ, Vulcano-Milazzo fault zone; PVFZ, Patti-Valley fault zone, TNFZ, Tindari-Novara fault zone, TBD, Tindari-Barἀcellona depression). B) Kinematic reconstruction and structural architecture of the northern sector of the Aeolian-Tindari-Letojanni fault system (ATLFS). 111

5 NW-SE trending faults (i.e VMFZ, PVFZ and TNFZ) show en-echelon configuration and form pull-apart (e.g. along the Lipari-Vulcano complex) and dilatational stepovers (e.g. the Tindari- Barcellona depression) in the overlapping sectors. This faults configuration and their current activity is clearly depicted by earthquakes clustering in the area whilst right-lateral kinematics on the NW-SE major faults and normal on the NE-SW trending structures is strongly supported by computed focal solutions and geodetic data (Fig. 3A). Our interpretation shows that the active deformation pattern of the study area is currently expressed by NW-SE trending, right-transtensional én-echelon fault segments whose overlapping gives rise to releasing stepover and pull-apart structures. This structural architecture has favored magma and fluid ascent and the shaping of the Lipari-Vulcano volcanic complex. Similarly, the Gulf of Patti is interpreted as an extensional relay zone between two overlapping, right-lateral NW-SE trending master faults. Notably, most of the low-magnitude instrumental seismicity occurs within the relay zones, whilst the largest historical earthquakes (1786, Mw=6.2; 1978, Mw=6.1) are located along the major fault segments (Fig. 3B). Finally, our investigations confirm that ATLFS is a prominent fault belt playing a primary role in the seimotectonic of the southern margin of the Calabrian Arc where it accommodates deformation between two main lithospheric domains characterized by different stress regimes. References Barreca, G., V. Bruno, F. Cultrera, M. Mattia, C. Monaco and L. Scarfì (2014). New insights in the geodynamics of the Lipari-Vulcano area (Aeolian Archipelago, southern Italy) from geological, geodetic and seismological data, Journal of Geodynamics, 82, ; Billi A., Barberi G., Faccenna C., Neri G., Pepe F. & Sulli F. (2006) - Tectonics and seismicity of the Tindari Fault System, southern Italy: Crustal deformations at the transition between ongoing contractional and extensional domains located above the edge of a subducting slab. Tectonics, 25, TC2006, doi: /2004tc Gasparini, C., Iannacone, G., Scandone, P., Scarpa, R., Seismotectonics of the Calabrian Arc. Tectonophysics 82, Palano M., Ferranti L., Monaco C., Mattia M., Aloisi M., Bruno V., Cannavò F., Siligato G. (2012) GPS velocity and strain fields in Sicily and southern Calabria, Italy: Updated geodetic constraints on tectonic block interaction in the central Mediterranean. Journal of Geophysical Research, vol. 117, b07401, doi: /2012jb Scarfì L., Barberi G., Musumeci C. Patanè D. (2016) - Seismotectonics of Northeastern Sicily and Southern Calabria (Italy): New constraints on the tectonic structures featuring in a crucial sector for the Central Mediterranean geodynamics. Tectonics, 35, , doi: /2015tc Rovida, A., Camassi, R., Gasperini, P., Stucchi, M., (2011): CPTI11, the 2011 version of the Parametric Catalogue of Italian Earthquakes. INGV, Milano, Bologna, DOI: /INGV. IT-CPTI