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Structural architecture and active deformation pattern
in the northern sector of the Aeolian-Tindari-Letojanni fault system
(SE Tyrrhenian Sea-NE Sicily) from integrated analysis of field,
marine geophysical, seismological and geodetic data
Fabrizio Cultrera (1), Giovanni barreCa (1, 7), luiGi Ferranti (2, 7), Carmelo monaCo (1, 7),
Fabrizio PePe (3), Salvatore PaSSaro (4), Graziella barberi (5), valentina bruno (5),
PierFranCeSCo burrato (6), mario mattia (5), Carla muSumeCi (5) & luCiano SCarFì (5)
ABSTRACT
Framed in the current geodynamics of the central Mediterrane-
an, the Aeolian-Tindari-Letojanni fault system is part of a wider NW-
SE oriented right-lateral wrench zone which accommodates diverging
motion between regional-scale blocks located at the southern edge
of the Calabrian Arc. In order to investigate the structural architec-
ture and the active deformation pattern of the northern sector of this
tectonic feature, structural observations on-land, high and very-high
resolution seismic reflection profiles, swath bathymetry and seismo-
logical and geodetic data were merged from the Lipari-Vulcano vol-
canic complex (central sector of the Aeolian Islands) to the Peloritani
Mountains across the Gulf of Patti. 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 flu-
id 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.
The structural configuration we reconstruct is also supported by seis-
mological and geodetic data which are consistent with kinematics of
the mapped 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 ma-
jor fault segments.
Key wordS: Southern Tyrrhenian sea, NE Sicily, seismic
reflection profiles, structural analysis, seismology, GPS
geodesy.
INTRODUCTION
The Aeolian-Tindari-Letojanni fault system (herein-
after ATLFS) is a regional deformation belt that extends
from the central sector of the Aeolian Islands to the Ionian
coast of Sicily, north of Mt. Etna, cutting across different
pre-existing tectonic domains (Fig. 1): i) stretched conti-
nental crust of the southern Tyrrhenian basin, ii) continen-
tal crust of the Calabrian Arc, iii) old transitional crust of
the Ionian basin subducted beneath Calabria (lanzaFame &
bouSquet, 1997; de Guidi et alii, 2013; barreCa et alii, 2014;
Palano et alii, 2012; 2015). This tectonic feature plays a key
role in the current geodynamics of the central Mediterra-
nean, dominated by the long-living convergence between
Africa and Eurasia (dewey et alii, 1989; FaCCenna et alii,
2001), and has been variously interpreted as: i) a crustal
transfer zone between the northern Sicily contractional
belt and the Ionian accretionary wedge (GoeS et alii, 2004;
neri et alii, 2004; billi et alii, 2006); ii) a lithospheric tear
fault, which bounds the western edge of the subducting
Ionian slab and has accommodated the south-eastward
shift of the overlying Calabrian Arc (rehault et alii, 1987;
van dijK & oKKeS, 1991; niColiCh et alii, 2000; doGlioni et
alii, 2001; FaCCenna et alii, 2004; roSenbaum et alii, 2008;
Chiarabba et alii, 2008; Palano et alii, 2012); iii) the sur-
face expression of a STEP fault (GoverS & wortel, 2005;
Polonia et alii, 2011; 2016; arGnani et alii, 2007; 2014;
GutSCher et alii, 2016; SCarFì et alii, 2016); iv) a transform
fault, extending from the Aeolian volcanic arc to the Ioni-
an Sea, that accommodates contraction in northern Sicily
and extension in western Calabria (lanzaFame & bouSquet,
1997; Palano et alii, 2012; barreCa et alii, 2014).
Evidences that the ATLFS is still active in its northern
sector are provided by seismological, geodetic and geolog-
ical data (e.g. neri et alii, 2005; billi et alii, 2006; Palano
et alii, 2012; barreCa et alii, 2014; SCarFì et alii, 2016;
Cultrera et alii, 2017). Over the period 1984–2014, about
1800 earthquakes with small-to-moderate magnitude (1.0
≤Ml≤ 4.8) and a maximum hypocentral depth of 40 km
have been localized close to this tectonic structure (barreCa
et alii, 2014). Historical catalogues reveal that this area was
affected by several strong earthquakes 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 locali-
ties (GaSParini et alii, 1982, 1985; rovida et alii, 2011). Fault
plane solutions mainly reveal dextral strike-slip and sub-
ordinately reverse focal mechanisms in the central sector
of the Aeolian islands, where the ATLFS system connects
with the eastern branches of the Sisifo-Alicudi transpres-
sional fault belt (Pondrelli et alii, 2004, 2006; billi et alii,
Ital. J. Geosci., Vol. 136, No. 3 (2017), pp. 00, 10 figs. (doi: 10.3301/IJG.2016.17)
© Società Geologica Italiana, Roma 2017
(1) Dipartimento di Scienze Biologiche, Geologiche e Ambientali
- Sezione di Scienze della Terra, Università di Catania. Corresponding
author e-mail: fcultrera@unict.it.
(2) Dipartimento di Scienze della Terra, delle Risorse e dell’Ambi-
ente, Università di Napoli “Federico II”.
(3) Dipartimento di Scienze della Terra e del Mare, Università di
Palermo.
(4) Istituto per l’Ambiente Marino Costiero, C.N.R. Napoli.
(5) Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio
etneo, Catania.
(6) Istituto Nazionale di Geofisica e Vulcanologia, Roma 1.
(7) CRUST - Centro Interuniversitario per l’Analisi Sismotettoni-
ca Tridimensionale con applicazioni territoriali.
F. CULTRERA ET ALII2
2010), dextral-normal strike-slip mechanisms in the Gulf
of Patti and prevailing normal faulting along the on-land
part of the ATLFS (neri et alii, 2005; GiammanCo et alii,
2008; barreCa et alii, 2014; SCarFì et alii, 2016).
Geodetic data (mattia et alii, 2009; Palano et alii, 2012;
2015) point out ~3,6 mm/yr of right transtensional motion
along a N126E direction in NE Sicily. This displacement
results in dextral transtension on the NW-striking ATLFS
and represents ~70% of the 5 mm/yr of regional right-lat-
eral differential motion between the Sicilian and the Cal-
abrian blocks (GoeS et alii, 2004; Palano et alii, 2012). Field
data along the Aeolian and Peloritani segments of the AT-
LFS highlight Quaternary activity with predominantly ex-
tensional and subordinately strike-slip kinematic features
(loCardi & naPPi, 1979; Frazzetta et alii, 1982; ventura,
1994; mazzuoli et alii, 1995; tortoriCi et alii, 1995; billi et
alii, 2006; de Guidi et alii, 2013; Cultrera et alii, 2017).
Although it is widely accepted that the ATLFS repre-
sents a key tectonic element in the geodynamics, volcanism
and seismicity of southern Tyrrhenian Sea and north-east-
ern Sicily, several issues about its structural pattern (i.e.,
distribution, attitude, and slip of fault segments) are still
unsolved. Particularly: 1) a comprehensive correlation be-
tween the offshore and onshore sectors has not been at-
tempted; 2) a link between faults and seismicity has not
been established. These limitations result in the lack of an
exhaustive seismotectonic model for the area.
Because of the occurrence of fault segments both on-
land and in the offshore, the reconstruction of the structur-
al architecture and of the active deformation pattern of the
northern sector of the ATLFS, where it propagates from
stretched to continental crust, was based on merging of
i) structural data, ii) multibeam bathymetry, iii) high and
ultra-high resolution single channel reflection seismics, iv)
seismological data, and v) geodetic data. Data presented
here allow to link regional shallow (geodetic and field data,
high-resolution marine geophysics) with deeper (seismo-
logical data) crustal scale structures. The achieved results
allow the understanding of the seismotectonics of the AT-
LFS and of its geodynamic significance.
REGIONAL TECTONIC SETTING
The tectonic setting of north-eastern Sicily is better un-
derstood when it is framed in the geodynamic scenario of
the central Mediterranean, which is dominated by the ~N-S
Neogene to Quaternary convergence between the Europe-
an and African continental margins (barberi et alii, 1973;
dewey et alii, 1989; FaCCenna et alii, 2001). Progressive con-
vergence has led to the formation of two major intercon-
nected tectonic domains: the Apenninic contractional belt,
which in north-eastern Sicily and Calabria is represented
by the arc-shaped Calabrian Arc, and the Tyrrhenian exten-
sional basin at the rear (inset in Fig. 1A).
The Calabrian Arc represents the sub-aerial portion
of a larger accretionary prism in the Ionian Sea, formed
in response to the Late Miocene-Quaternary subduction
of the Ionian realm, a 15-20 km thick crustal remnant
(Catalano et alii, 2001; vai, 2003) of a Permo-Triassic ocean
(the Neo-Tethys, ŞenGör, 1979). To the west, it is adjacent
to the Pelagian foreland domain (ben-avraham & GraSSo,
1991; Fig. 1A), which also includes the 25–30 km thick
continental crustal portion of the Hyblean Plateau in SE
Sicily (HP in Fig. 1A). The transition (continental to oce-
anic) between these two lithospheric compartments occurs
along the Malta Escarpment in the near offshore of eastern
Sicily (Fig. 1A), a Mesozoic passive margin which has been
reactivated by oblique extension during Plio-Quaternary
(SCandone et alii, 1981; Fabbri et alii, 1982; CaSero et alii,
1984; bianCa et alii, 1999).
The Calabrian Arc in north-eastern Sicily is formed
by the inner Calabro-Peloritan Nappe (CPN) which over-
thrust the Sicilian fold and thrust belt (SFTB). The CPN
(Fig. 1A) constitutes the backbone of the Peloritani Mts.
and consists of imbricate sheets of Hercynian metamorphic
rocks of the European paleo-margin and their Meso-Ceno-
Fig. 1 - A) Tectonic sketch map of the Central Mediterranean area
showing the major structural domains with major tectonic boundaries
draped (modified from Cultrera et alii, 2015). The Calabro-Peloritani
Nappe (CPN) represents the emerged portion of the Calabrian Arc
accretionary complex. Black line with triangles represents the front of
the Sicilian Fold and Thrust Belt (SFTB), a Neogene fold and thrust
system that tectonically lies atop the flexured Hyblean Plateau fore-
land (HP). B) 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-Ali-
cudi transpressional fault belt (SAFS). The yellow stars represent the
location of the Mw=6.2, 1786 and Mw=6.1, 1978 earthquakes. Dashed
black line contains the investigated area.
STRUCTURAL ARCHITECTURE AND ACTIVE DEFORMATION PATTERN IN THE NORTHERN SECTOR OF THE AEOLIAN-TINDARI-LETOJANNI FAULT SYSTEM 3
zoic sedimentary covers (oGniben, 1969). The Neogene to
Quaternary SFTB (Fig. 1A), mainly exposed in central and
western Sicily, consists of Meso–Cenozoic carbonate and
silicoclastic successions of the African paleo-margin that
over-thrusts the flexed Pelagian foreland (Fig. 1A).
The Tyrrhenian Sea is a back-arc basin related to the
Late Miocene-Middle Pleistocene subduction and rollback
of the Ionian oceanic lithosphere (barberi et alii, 1973;
malinverno & ryan, 1986; SCaraSCia et alii, 1994; GueGuen
et alii, 1998; Gvirtzman & nur, 1999; doGlioni et alii, 2001;
PePe et alii, 2000, 2003; FaCCenna et alii, 2001, 2004). A 70°
NW-dipping Benioff-Wadati zone beneath the southern
Tyrrhenian basin has been documented since the early
1970s (Chiarabba et alii, 2005 and reference therein) and
is well depicted by crustal earthquakes occurring down to
600 km depth (FrePoli et alii, 1996) and by a high-veloc-
ity seismic anomaly in the mantle (SelvaGGi & Chiarabba,
1995; FaCCenna et alii, 2004; neri et alii, 2012).
The north-westward subduction of the Ionian lith-
osphere beneath the Tyrrhenian basin has been accom-
modated by wrenching at its edges (barreCa et alii, 2016;
GutSCher et alii, 2016; Polonia et alii, 2016) which favored
the progressive south-eastward migration of the Calabri-
an Arc (wortel & SPaKman, 2000; GoverS & wortel, 2005).
According to many authors (e.g. GoverS & wortel 2005;
Polonia et alii, 2011; 2016; neri et alii, 2012; SCarFì et alii,
2016), the surface expression of the lithosphere tearing
at the slab edge along the southern margin of the Cal-
abrian Arc, interpreted as a STEP fault (sensu GoverS &
wortel 2005), is currently represented by the NW–SE
trending right-lateral strike-slip ATLFS in north-eastern
Sicily (Fig. 1B). It extends from the central sector of the Ae-
olian archipelago to the Ionian coast of Sicily and separates
two different tectonic domains. To the west of the ATLFS,
a seismically active contractional belt extends from Ustica
Island to the central sector of Aeolian islands (Pondrelli et
alii, 2004; neri et alii, 2005; billi et alii, 2006, 2007, 2011;
Palano et alii, 2012) where it is probably accommodated
by the ~100 km long Sisifo-Alicudi transpressional fault
system (SAFS, Fig. 1B; barreCa et alii, 2014 and referenc-
es therein). Geodetic velocities show that the contraction-
al belt accommodates a 1-1.4 mm/yr shortening (Palano
et alii, 2012). To the east, the ATLFS limits an extensional
belt in northeastern Sicily and southern-western Calabria
(monaCo & tortoriCi, 2000; neri et alii, 2004; Pondrelli et alii,
2006; Ferranti et alii, 2008; mattia et alii, 2009; SerPelloni
et alii, 2010; CuFFaro et alii, 2011). Geodetic data document
an integrated extension of 1.4 mm/yr in western Calabria
(d’aGoStino et alii, 2011). As a consequence, the ATLFS
accommodates 3.6 mm/yr of right-lateral transtensional
motion between the adjacent compartments (mattia et alii,
2009; Palano et alii, 2012).
FIELD STRUCTURAL ANALYSIS
methodS
Structural data in the Lipari-Vulcano complex and Pe-
loritani sectors have been collected on 80 sites of meas-
Fig. 2 - Multidisciplinary dataset
considered in this study. Data con-
sist 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.
F. CULTRERA ET ALII4
Fig. 3 - A) Morpho-structural map of the Lipari island. B) Stereoplot of detected faults with relative slip
vectors and cumulative rose diagrams showing the azimuth distribution of dikes and fractures. C) NW–SE
to NNW-SSE extensional fault planes detected along the south-eastern sector of the island, where (D)
WNW-ESE to E-W pure strike-slip structures have been also observed. E) NE-SW trending extensional
fault segments affecting the western sector of Lipari, south-west of Sant’Angelo Mt. F) Morpho-structural
map of the Vulcano island. G) Stereoplot of detected faults with relative slip vectors and cumulative rose
diagrams showing the azimuthal distribution of dikes and fractures. H) NNE-SSW trending extensional
fault segments affecting the central sector of the island, where they offset pyroclastic rocks of 5-10 cm.
I) NE-dipping normal faults dislocating of about 10 cm a well-bedded sequence of pyroclastic deposits
outcropping in the south-eastern cliff of the Vulcano island. L) tecto-grooves and Riedel fractures along a
WNW-ESE trending strike-slip fault plane affecting the M. Lentia domes.
STRUCTURAL ARCHITECTURE AND ACTIVE DEFORMATION PATTERN IN THE NORTHERN SECTOR OF THE AEOLIAN-TINDARI-LETOJANNI FAULT SYSTEM 5
urements (Fig, 2). Data consist of meso-fault and fracture
plane attitudes. Movement directions along faults planes
have been obtained by steps, grooves, rarely slickenlines
and Riedel fractures. Data have been properly represented
by using Schmidt lower hemisphere convention.
For the Lipari-Vulcano volcanic complex, dikes ori-
entation has been used in order to verify a correspond-
ence between tectonic structures and volcanic features.
Radial, curved and open faults and faults parallel to main
crater-caldera rims were not taken into account, being re-
lated to volcanic processes (e.g. ring faults GudmundSSon,
2008, see also ruCh et alii, 2016). Preliminary structur-
al data analysis allowed us to discriminate the faulting
mechanism (e.g tectonics or volcanic) responsible of
their nucleation (see also barreCa et alii, 2014 for more
details). The age of volcanic rocks was taken from pub-
lished geological maps (Servizio GeoloGiCo d’italia, 2011;
luCChi, 2013).
Field data From the liPari-vulCano ComPlex
The Lipari–Vulcano complex (Fig. 1B) consists of a
~25 km long NNW–SSE oriented volcanic belt rising from
about 1 km below sea level to the maximum 500 and 600
m a.s.l. elevations of Vulcano and Lipari islands, respec-
tively, and emplaced on a 15–20 km thick continental crust
belonging to the stretched Tyrrhenian basin (boCCaletti et
alii, 1990; niColiCh et alii, 2000; niColiCh, 1989; Piromallo &
morelli, 2003). The Lipari–Vulcano complex is the result
of distinct eruptive phases occurred from ∼220 kyr ago up
to historical times (Gillot, 1987, luCChi, et alii, 2013), with
andesitic products of high-K calc-alkaline to shoshonitic
affinity ejected from several volcanic centers (PeCCerillo,
2005; luCChi et alii, 2013).
Structural data collected on Lipari island (Fig. 3A) con-
sist of faults and fractures involving products younger than
42 ka (Servizio GeoloGiCo d’italia, 2011; luCChi et alii, 2013).
Faults mainly consists of sub-vertical dip-slip planes show-
ing displacement of few cm to ~1 m and are distributed ac-
cording to three prevalent trends (see plot in Fig. 3B). The
most representative set is oriented NW–SE to NNW-SSE
(N120-170E) and it is characterized by faults planes with dip-
slip motion (Fig. 3C), and locally with right-oblique motion
(pitches ranging between 95 and 140°). Along the SW sector
of the island, this fault system forms a ~50 m wide shear
zone with negative-flower geometries that appear to control
the coastal morphology. Fault planes show well-preserved
sub-horizontal slickenlines and Riedel fractures indicating a
right-lateral component of motion. Although less represent-
ed, evidence of pure strike-slip features can be found along
the south-eastern sector of the island, where WNW-ESE to
E-W oriented fault planes, with sub-horizontal slickenlines
suggest right-lateral motion (Fig. 3D). The NE-SW trend-
ing set (N30–50E) exclusively consists of normal faults with
planes mainly dipping at 70–80◦, showing dm-scale displace-
ments of ~25 ka old volcanic products (Fig. 3E). They main-
ly outcrop along the south-eastern sector of the island and
seem to terminate against the NW-SE faults.
As a whole, detected faults are accompanied by var-
iously oriented fractures (see directional statistics in
Fig. 3B) which consist of joints and gypsum-filled tension
gashes mainly outcropping along the western sector of the
island, where hydrothermally altered rocks (kaolinite) out-
crop. As regards the dikes distribution, a major concentra-
tion in the N20–30E azimuthal range has been detected
(see directional statistics in Fig. 3B)
The island of Vulcano (Fig. 3F) is characterized by
normal faults and fractures affecting products younger
than 50 ka (Servizio GeoloGiCo d’italia, 2011; luCChi et alii,
2013). Faults are mostly distributed into two major NNE-
SSW and NW–SE trending systems (see plot in Fig. 3G).
The NNE-SSW (N10–20E) oriented set is the most wide-
spread. Faults have an average dip at 70° and are char-
acterized by dip-slip motion. In the central sector of the
island, they generally dislocate of 5-10 cm well-stratified
pyroclastic rocks (Fig. 3H). Fault zones are characterized
by micro-sized cataclastic breccia and are often accompa-
nied by synthetic structures at 15–20° with respect to the
main displacement zones. Faults belonging to this system
have been also found along coastal cliffs in the eastern
sector of the island. In the south-eastern portion of the is-
land, NE-dipping normal faults dislocate of about 10 cm a
well-bedded sequence of pyroclastic deposits and are often
accompanied by parallel fractures with a minor dip value
(Fig. 3I). The NW–SE oriented set is mainly characterized
by normal faults with planes dipping at 60°–70◦. In the NW
corner of the island, WNW-ESE to NW-SE trending faults
and fractures cross-cut the 25-15 ka old Lentia lava domes
and older rims. Some faults exhibit 1 m wide damage zone,
hosting fine-grained breccia. Slickenlines and Riedel frac-
tures on their surfaces indicate a dextral-lateral compo-
nent of motion (pitch of ∼170◦; Fig. 3L). Joints and dikes,
well exposed in the southern cliffs of the island, are mainly
distributed in the N20E to N110E trends, respectively (see
directional statistics in Fig. 3G).
Field data From the Peloritani mtS. SeCtor
Structural analysis along the coastal sector of Pelor-
itani Mts. highlighted the occurrence of three fault pop-
ulations characterized by different trend and kinematics
(see plots in Fig. 4A). The main set is represented by a
NW-SE to NNW-SSE trending right-oblique (transten-
sional) fault zone which extends for ~20 km from Capo
Tindari to Novara village (Tindari-Novara fault zone,
TNFZ; Fig. 4A). This fault system bounds to the west a tri-
angular-shaped morphological depression (Fig. 4A, Tin-
dari-Barcellona tectonic depression, billi et alii, 2006),
developed from the Tindari-Barcellona coastal area to
the Novara village southwards, and filled by Plio-Qua-
ternary marine to continental deposits (di SteFano &
lentini, 1995). In the Capo Tindari area, where mainly
Hercynian metamorphic rocks outcrop, exposed fault
planes consists of N150E to N160E dip-slip structures,
dipping to the NE at 65-80° (Fig. 4B) and locally show-
ing minor dextral strike-slip components of motion (see
inset in Fig. 4B). These faults are frequently accompanied
by 40° SW dipping closely-spaced antithetic structures
(Fig. 4C). To the south, between Belvedere and Novara
villages, the TNFZ exhibits a ~N150E oriented, dipping
at ~70° toward NE, 150 to 300 m high fault scarp which
appears to be the south-eastern structural continuation
of the Capo Tindari coastal cliff. Near the Tripi village,
a ~N150E oriented, ~70° NE dipping fault offset the up-
per Oligocene-Early Miocene Capo D’Orlando flysch for-
mation (lentini et alii, 2000) and exhibits a ~150 m high
fresh fault scarp (Fig. 4D). Exposed fault planes along
the cataclastic zone (see inset in Fig. 4D) mainly consist
F. CULTRERA ET ALII6
Fig. 4 - A) Morpho-structural map of the Peloritani sector. Inset shows a cumulative plot of detected faults with relative slip vectors. The Tin-
dari-Novara fault zone (TNFZ) consists of an array of NW-SE trending right-lateral fault segments which roughly extends from Capo Tindari
to Novara village. B) N150E oriented, NE dipping extensional fault detected along the Capo Tindari cliff showing a minor dextral strike-slip
component of motion (see inset). The fault segments belonging to the TNFZ are frequently accompanied by (C) 40° SW dipping closely-spaced
antithetic structures. D) N150E oriented, ~70° NE dipping fault that offsets the Capo D’Orlando flysch formation and forms a ~150 m-high
fresh fault scarp. Exposed fault planes along the cataclastic zone (see inset) mainly consist of N150-160E oriented closely-spaced extensional
(or transtensional) faults. E) N5-25E oriented extensional fault, dipping to WNW at about 70-80° and outcropping within the Tindari-Barcel-
lona depression. F) N40-50E trending, NW dipping extensional fault that, in the Villafranca Tirrena area, deforms middle Pleistocene clays
with intercalations of volcanic ashes.
STRUCTURAL ARCHITECTURE AND ACTIVE DEFORMATION PATTERN IN THE NORTHERN SECTOR OF THE AEOLIAN-TINDARI-LETOJANNI FAULT SYSTEM 7
of N150-160E oriented closely-spaced extensional fault
planes with doubtful component of dextral motion.
The second set consists of N5-25E oriented extensional
faults, mainly dipping to WNW at about 70-80° (Fig. 4E)
and exclusively outcropping within the Tindari-Barcellona
tectonic depression. These faults probably favor the pres-
ence of some geothermal springs and mantle-related gas
vents (CO2 and He, GiammanCo et alii, 2008), which appear
distributed along a NNE trend (yellow circles in Fig. 4A).
Moreover, within the Tindari-Barcellona-Novara depres-
sion, this set of faults appears to control the drainage pat-
tern trend (Fig. 4A).
A further set of faults bounds to the south-east the Tin-
dari-Barcellona tectonic depression (Fig. 4A) and consists
in NE-SW extensional structures which sometimes exhibit
Quaternary sin-sedimentary activity (di SteFano & lentini,
1995). Fault planes are N40-50E oriented, NW dipping (55-
70°), and are characterized by dip-slip motion and offsets
ranging from 0.5 to 20 m. Toward the north-east, between
San Filippo del Mela and Villafranca Tirrena villages, this
set of discontinuities deforms middle Pleistocene clays
with intercalations of volcanic ashes (Fig. 4F).
MARINE GEOPHYSICAL DATA AND INTERPRETATION
methodS
The marine geophysical data were acquired in January
2014, onboard of the R⁄V Urania of the National Research
Council (CNR). The multibeam survey covered about 1100
km² of seafloor surface (Fig. 2) in the -1276/-22 m (b.s.l.)
depth range including a partial view of the Patti and Milaz-
zo shelves, the slope area comprised between the northern
Sicily coast and a partial view of the distal, SE sector of
the Vulcano island. The Digital Terrain Model (DTM) of
the Gulf of Patti results from a dataset acquired using an
EM710 Simrad (Kongsberg©inc) bathymetric echo-sound-
er, which emits more than 400 beams included in a 140°
swath coverage for each ping. This equipment allows to
collect soundings until 2800 m below the sea-floor (bsf).
All pings were manually processed to remove data outliers
using the Fledermaus 3D software. The processed depth
measurements were then organized in 20X20 m regularly
spaced matrix.
A dense grid (~500 km-long) of high-resolution seismic
reflection profiles was also recorded along the continen-
tal shelf and the upper slope of the Gulf of Patti (Fig. 2),
with the aim to detect the possible offshore extension of
fault systems mapped on the Lipari–Vulcano complex and
on the coast of the Peloritani Mts. The acoustic source
for seismic prospecting was a 1 kJ Sparker power supply
with a multi-tips Sparker array. The acoustic signals were
recorded with a single-channel streamer having an active
section of 2.8 m. Navigation was controlled by a DGPS sys-
tem. Data processing was performed using the Geo-Suite
AllWorks software package running a series of mathemati-
cal operators including: a) true amplitude recovery using a
T2 spherical divergence correction; b) band-pass (300-2000
Hz) “finite impulse response” filter using a filter length of
256 samples; c) de-ghosting, d) swell-filter; e) time migra-
tion; f) trace mixing of three traces for enhancing hori-
zontal signal; g) time variant gain to boost amplitudes of
deeper arrivals; h) mutes to eliminate the signal noise on
the water column. Signal penetration was locally found to
exceed 250 ms t.w.t.
Further, a set of ultra-high resolution reflection seis-
mic data was recorded by using the Chirp II (Benthos©inc)
chirp sub-bottom profiler that operates with 16 transduc-
er in a wide frequency band (2–7 kHz) with a chirp pulse
of 20–30 ms. The lines run mainly along NE-SW direction
and are tied by lines acquired in NW-SE direction (see
Fig. 2). Data processing includes: a) true amplitude re-
covery using a T2 spherical divergence correction, b) time
variant gain to boost amplitudes of deeper arrivals and c)
mutes to eliminate the signal noise on the water column.
Signal penetration was found to exceed 90 ms two-way
time (t.w.t.) in the deeper sector of the slope off the AMBK.
Vertical resolution is up to 5 cm in near subseafloor.
The seismic lines were depth-converted by using spe-
cific values of acoustic wave velocity. In the study area, an
average value of 1515 m/s for the sound speed on the water
column was calculated using data recorded by the “RE-
SON SVP20” sound velocity profiler. As no information is
available on the velocities of seismic units, we have adopt-
ed average velocities from litho-stratigraphy and sonic log
data available for coeval deposits in wells drilled offshore
in southern and western Sicily (also see PePe et alii, 2010
for details). The values we have used are 1650 and 1800
m/s for the post Last Glacial Maximum and Upper Quater-
nary sedimentary rocks, respectively.
morPho-bathymetriC data
The investigated area is characterized by a narrow
(1-4 km wide) continental shelf approximately developed
from east to west for about 20 km (Fig. 5) and by a 15°
north-dipping continental slope (see Fig. 5 and profile A-A’)
on which several ridges and canyons are present. In the
central sector, the continental slope is interrupted by a
marked bathymetric culmination, the Patti Ridge, which
separates the Gioia Basin, to the east, from the Finale Ba-
sin to the west, and represents the main morphological fea-
ture of the Gulf of Patti (see Fig. 5 and profile B-B’). In its
central portion, the Patti Ridge rises up to 450 m b.s.l. and
extends for approximately 15 km towards NW, connecting
the continental shelf to the southern margin of the Vulcano
edifice, which rests on a stretched continental crust. Later-
ally, the Patti Ridge is bounded by two incisions: the Patti
Valley, to the west, and the Milazzo canyon, eastward (see
Fig. 5 and profile C-C’). The latter represents the most im-
portant drainage feature of the investigated area. It is ex-
pressed by a NW-SE trending, ~15 km long and more than
300 m deep (see profile D-D’ in Fig. 5) submarine incision,
which bifurcates upstream in the two minor Colantoni and
Fanucci branches. Here, an intense retrogressive erosion
accompanied by diffuse gravitational deformations was
singled out (see Cultrera et alii, 2017).
hiGh-reSolution reFleCtion SeiSmiCS
Seismic profiles acquired in the Gulf of Patti imaged
a well-layered package of laterally continuous, high-am-
plitude reflectors. The imaged seismic sequence shows
a ∼400 m thick succession that can be attributed to the
Middle-Late Pleistocene-Holocene, based on correlation
with published seismic reflection data (Fabbri et alii, 1981,
F. CULTRERA ET ALII8
Fig. 5 - Morpho-bathymetric map of the Gulf of Patti (DTM cell size 20X20 m) and traces of bathymetric profiles (black lines) with the rel-
ative cross sections.
STRUCTURAL ARCHITECTURE AND ACTIVE DEFORMATION PATTERN IN THE NORTHERN SECTOR OF THE AEOLIAN-TINDARI-LETOJANNI FAULT SYSTEM 9
Gabbianelli et alii, 1996; CuPPari et alii, 1999; arGnani et alii,
2007; Cultrera et alii, 2017).
Seismic profiles allowed to detect a main NW-SE
trending set of faults accompanied by subordinate N-S to
NNE-SSW trending faults. The seismic data coupled with
those available in literature (e.g. Gabbianelli et alii, 1996;
CuPPari et alii, 1999; Colantoni et alii, 2001; arGnani et alii,
2007; Cultrera et alii, 2017) allow to obtain the new struc-
tural map shown in Fig. 6A.
NW-SE striking faults are widespread all over the in-
vestigated area and, as they appear in the seismic profiles,
mainly consist of extensional structures. SW dipping faults
are concentrated along the Patti Valley (Fig. 6A) where they
involve Holocene deposits and exhibit vertical displacements
of about 3 m (Line CHP 43, Fig. 6B) that progressively van-
ishes at their tip (Line CHP 35, Fig. 6C). These fault segments
belong to a fault zone, here called Patti Valley Fault Zone
(PVFZ), which develops for about 12 km with a NW-SE trend
and it is associated to a SW dipping, 5-15 m-high fault scarp
(see morpho-bathymetric map and profile C-C’ in Fig. 5).
NE dipping faults are mainly distributed along the east-
ern slope of the Patti Ridge where they form a fault zone
extending from the SE flank of the Vulcano Island to SW
of Capo Milazzo (Vulcano-Milazzo fault zone, VMFZ in
Fig. 6A). Vertical displacements observed along this fault
zone reach ∼150-200 m and form prominent fault scarps
characterized by diffuse gravitational deformation (Fig. 6D).
An isolated set of N-S to NNE-SSW trending extension-
al faults occurs in the southern sector of the Gulf of Pat-
ti. Faults exhibit small displacements rarely larger than a
few tens of meters and some of them deform the seafloor
producing 5 m-high fault scarps (Fig. 6E). Faults belong-
ing to the NNE-SSW to N-S trending extensional system
and displaying possible negative flower geometry are ob-
served in the central sector of the profile SP 19 (see pro-
file in block diagram of Fig. 7). Some faults are sealed by
Upper Quaternary sediments but small-scale faults cutting
the sea-bottom can be observed. To the east (north of the
Capo Milazzo Peninsula), extensional faults form a prom-
inent horst structure which appear to be superimposed on
Fig. 6 - A) Morpho-structural map of the Gulf of Patti as obtained by interpreting the whole seismic profiles dataset which allowed to detect
two main NW-SE trending fault zones (VMFZ, Vulcano-Milazzo fault zone; PVFZ, Patti-Valley fault zone) accompanied by subordinate N-S to
NNE-SSW trending faults. B) Chirp profile CHP 43 showing a SW dipping fault segment belonging to the PVFZ that involves Holocene deposits
and exhibits vertical displacements of about 3 m. C) Chirp profile CHP 35 showing a SW dipping active fault at the southern termination of the
PVFZ where it exhibits vertical displacements of about 2 m. D) Chirp profile CHP 41 showing a NE dipping fault affecting the eastern slope of
the Patti Ridge. Vertical displacements observed along these fault zone reach ∼150-200 m and form a prominent fault scarp characterized by dif-
fuse gravitational deformation. This fault is part of a larger fault zone extending from the SE flank of the Vulcano Island to SW of Capo Milazzo
(VMFZ). E) Chirp profile CHP 57 showing a NNE-SSW trending extensional fault affecting the southern sector of the Gulf of Patti. Fault clearly
deforms the seafloor and produces a 5 m-high fault scarp.
F. CULTRERA ET ALII10
previous contractional features (see sparker profile SP 19
Fig. 8). In the central part of the horst, growth strata asso-
ciated with a probable SW-dipping extensional fault can be
observed (see profile in block-diagram of Fig. 8).
SEISMOLOGICAL ANALYSIS
methodS
More than 2500 seismic events (0.6≤Ml≤5.3) occurred
between 1999 and 2015 (http://www.ct.ingv.it/ufs/analis-
ti/catalogolist.php; Gruppo Analisi Dati Sismici, 2016)
inside a wide sector (latitude 38.01°N–38.62°N and lon-
gitude 14.68°E–15.32°E) encompassing our study area
(Fig. 2). In order to improve the quality of the seismic da-
taset, the events have been relocated using the tomo DDPS
code (zhanG et alii, 2009) with the 3D velocity model by
SCarFì et alii, 2016. A map with the 2368 final locations
with at least 8 P- and S-phases observations and GAP≤280°
was built up (Fig. 9A). The inversion provided an improve-
ment in the quality of the locations with respect the initial
guess, with average locations uncertainty of 0.1 km in lat-
itude and longitude and 0.2 km in depth, a decrease of the
root-mean-square (RMS) residuals by about 68% (average
residual of 0.11 sec) and a higher clustering which empha-
sizes earthquake lineaments.
Following, in order to determine the displacement type
on seismogenic faults, and to improve our understanding of
the stress direction and tectonics of the area (e.g. d’amiCo
et alii, 2010, 2011), fault plane solutions (FPSs) of events
with magnitude Ml≥3.0 and focal depth less than 50 km
were computed by using the FPFIT program (reaSenberG &
oPPenheimer, 1985). Several polarities were extracted from
the “Sicily and southern Calabria focal mechanism data-
base” (http://sismoweb.ct.ingv.it/focal/; see SCarFì et alii,
2013), others were accurately re-picked from digital seismic
waveforms, and then inverted together with the rays traced
through the computed 3D velocity model. In addition, we
considered the moment tensor solutions dating back from
1977, published from the Italian CMT and RCMT catalogues
Fig. 7 - 3D view of the Spark-
er profile SP 19 which, in its
central sector, shows horst
and graben structures that
dislocate Holocene deposits.
Some faults are sealed by
Upper Quaternary sediments
but small-scale active faults
can be clearly observed.
STRUCTURAL ARCHITECTURE AND ACTIVE DEFORMATION PATTERN IN THE NORTHERN SECTOR OF THE AEOLIAN-TINDARI-LETOJANNI FAULT SYSTEM 11
(Pondrelli et alii, 2006, 2011; see also http://www.bo.in-
gv.it/RCMT/). This led to collect 68 well-constrained (aver-
aged uncertainties in strike, dip and rake less than 20°) crus-
tal FPSs (Fig. 9C). Rupture mechanisms (inset 1 in Fig. 9C)
show prevalently normal dip-slip and strike-slip movements
(in particular, 49% are normal and 44 % are strike-slip fault-
ing). Only a small minority exhibits reverse faulting. The
observed different styles of faulting is also accompanied by
changes in the attitude of the conjugate planes and in the
trend of computed P and T axes (see inset 2 in Fig. 9C).
SeiSmoloGiCal data
At least two main seismological domains may be clear-
ly distinguished. The first domain is characterized by steep
P-axes and horizontal T-axes which reveal a dominant ex-
tensional regime in north-eastern Sicily (i.e. in the main-
land between Capo Tindari and Capo Milazzo and south
of Capo d’Orlando; Fig. 9C). Most of the fault plane solu-
tions indicate NE-SW striking structures, whose direction
is consistent with the geometry suggested by some NW
dipping event clusters (see the southern part of section AA’
in Fig. 9B). Other earthquakes characterized by normal
motion with NNE-SSW to NE-SW striking nodal planes
were found in the Gulf of Patti coastal zone. The typical
seismogenic depth is between 5 and 15 km. The second do-
main, between the northern coast of Sicily and the Aeolian
Islands, shows similar depth but, differently, the focal solu-
tions clearly reveal dextral strike-slip kinematics on NW-
SE striking nodal planes (Fig. 9C), which fairly matches
the hypocenter’s distribution (see the event alignment in
the map of Fig. 9A and the sub-vertical clusters in the cen-
tral part of the section BB’ in Fig. 9B). A deeper seismicity,
down to 30 km, is found south of Capo Calavà (Fig. 9A,
B) where some strike-slip focal mechanisms, NW-SE ori-
Fig. 8 - 3D view of the easternmost portion of the Sparker profile SP 19, showing a horst structure affecting the offshore of the Capo Milazzo
peninsula. Growth strata associated with a SW dipping extensional fault probably superimposed on a previous contractional feature.
F. CULTRERA ET ALII12
ented have been computed. Reverse faulting mechanisms
characterize several events south of Salina, east of Lipari
and SW of Vulcano island, along NE-SW to E-W oriented
rupture nodal planes (Fig. 9C).
It is noteworthy that the pattern pinpointed by the
earthquake locations as well as the strike of the FPSs nodal
planes is well correlated with the trend of the mapped tec-
tonic features and with the velocity discontinuities showed
by the tomographic images of the area (Fig. 9B; redrawn
from SCarFì et alii, 2016). Intermediate and deeper events
(> 40 km) are located north of Capo Milazzo and east of
Capo Calavà (see Fig. 9A).
Fig. 9 - A) Map view of the final
seismic events location. Loca-
tion 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-Bar-
cellona depression). B) Vertical
sections (AA’, BB’) incorporate
all relocated events within 5
km of the cross-section lines).
(C) Map showing the 68 select-
ed fault plane solutions (low-
er-hemisphere projection). Inset
1: triangular diagram of focal
mechanisms (vertices represent
normal, thrust, and strike-slip
focal mechanisms (FrohliCh,
1992). Inset 2: plunges of P
(circles) and T (triangles) axes
have been used to divide focal
mechanism datasets into the
main stress regime categories,
according to the zobaCK (1992)
classification.
STRUCTURAL ARCHITECTURE AND ACTIVE DEFORMATION PATTERN IN THE NORTHERN SECTOR OF THE AEOLIAN-TINDARI-LETOJANNI FAULT SYSTEM 13
GEODETIC ANALYSIS
methodS
We re-processed the GPS sub-dataset already used in
mattia et alii, (2009) with the aim to focus our analysis
in the on-land sector of the ATLFS. The sub-dataset used
in this work has a time span of data acquisition ranging
from 1996 to 2008 by using both permanent and survey
GPS stations in the area of the Peloritani Mts extending
from the shoreline of Northern Sicily to Mt. Etna (see GPS
stations in Fig. 2). The details about the data processing
are available in mattia et alii (2009). Here we propose the
dilatation and horizontal shear strain rate maps, calcu-
lated from the velocities of the GPS stations, applying the
method described in haineS & holt (1993) and holt &
haineS (1995). This method adopts a spherical geometry
in terms of a rotation function using a bi-cubic Bessel
interpolation on a curvilinear grid with a variable spacing
of knots.
Fig. 10 - A) Dilatation
strain-rate map of the Pe-
loritani Mts sector. A clear
band of NW-SE oriented
dilatation can be observed
between the Tindari and
Novara GPS stations and
farther to the SE, support-
ing the transtensional sig-
nificance of the TNFZ. High
values of geodetic dilatation
can be observed also east
of Tindari station, corrob-
orating the extensional
deformation detected in the
Tindari-Barcellona depres-
sion (TBD). The coverage of
the GPS network was also
sufficient for the definition
of the strain axes. B) Shear
strain-rate map of the Pelo-
ritani Mts sector showing
a NW-SE oriented shear
deformation alignment
which extends from the Tin-
dari area to the SE, roughly
following the ATLFS and,
therefore, supporting the
lateral motion of its fault
segments. Black triangles
represent the permanent
and non-permanent GPS
station used in this work.
F. CULTRERA ET ALII14
GeodetiC data
Our previous studies based on GPS data analysis (mattia
et alii, 2008; barreCa et alii, 2014) evidenced ∼3.0 mm/yr of ac-
tive shortening between the Lipari and Vulcano islands, with
a maximum strain rate of about 1.0 × 10−13s−1 between La
Fossa and Vulcanello (Fig. 3F), with orientation varying from
N–S to NNW–SSE. Moreover, mattia et alii (2009) pointed out
the occurrence of a tensile and a dextral strike-slip compo-
nent of 1.4 ± 0.6 and 3.9 ± 0.6 mm/yr respectively across the
on-land sector of the ATLFS in NE Sicily. By taking into ac-
count a mean N35W fault trend, Palano et alii (2012) refined
these measurements and estimated about 3.6 mm/yr of mo-
tion along the N126E direction, resulting in dextral transten-
sion on the NW-striking ATLFS in NE Sicily.
In this study, we reconsidered the network geometry
and the estimated velocity at each site reported in mattia
et alii (2009) and then we calculated the horizontal strain
rate field. The dilatation strain-rate map in Fig. 10A clear-
ly shows a NW-SE oriented area where the values of dila-
tational deformation span from about 0.03 to 0.10 ·10-13
s-1. This broad deformation band roughly follows the Tin-
dari-Novara fault zone (TNFZ in Fig. 10A) and extends as
far as to the Ionian coast of Sicily. Higher values of geodet-
ic dilatation can be observed east to the Tindari GPS sta-
tion, in the Tindari-Barcellona depression (TBD, Fig. 10A).
The coverage of the GPS network was also sufficient for
the definition of the strain axes (see Fig. 10A).
An interesting information is also given by the shear
strain-rate map (Fig. 10B), which shows a NW-SE oriented
shear deformation alignment with values of about 0.10 ·10-
13 s-1 (Fig. 10B), spatially coincident with the dilatational
deformation one (see above).
DISCUSSION
The interpretation of collected field-structural and
marine geophysical data, integrated with seismological
and geodetic observations, allowed us to characterize the
tectonic setting and the active deformation pattern of the
northern sector of the ATLFS.
As regards the Lipari-Vulcano complex, the structur-
al analysis evidenced that the two islands are affected by
a main NW-SE to NNW-SSE trending right lateral tran-
stensional fault system, accompanied by NNE-SSW and
NE-SW oriented minor faults and fractures. These latter
discontinuities usually terminates against the NW-SE to
NNW-SSE oriented ones and are characterized by dip-slip
extensional motion (see Fig. 3). This fault configuration is
roughly consistent with a strike-slip regime, active since at
least 50 ka ago (barreCa et alii, 2014), in which the exten-
sional fractures and faults can be interpreted as pull-apart
and/or horsetail structures (see also mazzuoli et alii, 1995;
barreCa et alii, 2014). In this context, the Lipari–Vulcano
complex seems to be formed within an “en échelon” config-
uration of NW–SE to NNW-SSE oriented strike-slip faults
(Fig. 11) where the associated NNE-SSW to NE-SW trend-
ing normal faults and fractures have probably created the
favorable condition for magma ascent along the northern
sector of the ATLFS (see also ventura, 1994; GionCada et
alii, 2003; ruCh et alii, 2016).
Even though no clear transpressional or contraction-
al tectonic features were detected in the field, geodet-
ic and seismological data (mattia et alii, 2008; barreCa et
alii, 2014), as well as the geo-chemical history of the Li-
pari-Vulcano volcanism (GionCada et alii, 2003), suggest
that a contractional tectonic regime could have recently
superimposed on a previous transtensional one. According
to barreCa et alii, (2014), since 15 ka ago the northernmost
sector of the ATLFS has been involved in the eastward-mi-
grating Sisifo-Alicudi transpressional belt (SAFS in Fig 1B;
billi et alii, 2010; barreCa et alii, 2014) that, according to
geodetic data, may accommodate 1.4 mm/yr of the active
shortening presently occurring between northern Sicily
and Sardinia. The lateral transition from an extensional
to a contractional setting, also evidenced by the compres-
sive focal mechanisms between Salina and Lipari islands
(Fig. 9C), accounts for both the cessation of volcanism in
the western-central sector of the Aeolian Archipelago and
for geochemical change in the Lipari-Vulcano complex
(GionCada et alii, 2003; barreCa et alii, 2014) and can be
framed in the regional change in the stress pattern relat-
ed to the southern Tyrrhenian geodynamic reorganization
(GoeS et alii, 2004; billi et alii, 2010; Palano et alii, 2012).
To the south, the structural setting of the Gulf of Pat-
ti is still debated and to date contrasting hypothesis have
been proposed in literature. In particular, Gabbianelli et
alii, (1996); CuPPari et alii (1999); Colantoni et alii (2001)
postulated that a recent NW-SE oriented extensional or
transtensional fault system, developed from the Gulf of
Patti coastal area to the southern flank of the Vulcano
island, has superimposed on a Pliocene contractional or
transpressional one. Contrarily, arGnani et alii, (2007) re-
tained that since the Middle Pleistocene a NW-SE oriented
transpressional or contractional deformation belt, devel-
oped from Capo Milazzo to the Salina island, has superim-
posed on Pliocene extensional features.
The analysis of the high and very high-resolution ma-
rine geophysical dataset acquired in the Gulf of Patti, al-
lowed us to provide further constraints about its structural
setting and to better define the ongoing deformation pat-
tern. In particular, the interpretation of the seismic profiles
highlights two main NW-SE oriented fault zones (i.e. Vulca-
no-Milazzo fault zone, VMFZ; Patti Valley fault zone, PVFZ)
and subordinately, a NNE-SSW to N-S trending set of faults
(Fig. 6A). Due to limitation in a section view, is not possi-
ble to ascertain whether the NW-SE oriented fault segments
imaged by the seismic profiles (Figs. 6B-E) are also charac-
terized by a strike-slip component of motion, as observed
on-land for the similarly oriented set (i.e. along the TNFZ
and in the Lipari-Vulcano complex). However, an additional
constraint arises from the NW-SE hypocenter alignment of
the earthquakes located in the Gulf of Patti (see the map
in Fig. 9A and the section BB’ in Fig. 9B) which is spatial-
ly coherent with the shallow faulting systems. In particular,
the focal mechanisms computed for that NW-SE oriented
earthquakes cluster roughly aligned with the PVFZ (see Fig.
9C) show that ruptures mainly occur along NW-SE oriented
right-lateral nodal planes, hence supporting the hypothesis
of the possible right-transtensional motion of this ~12 km-
long, NW-SE oriented deformation belt. It mainly develops
along the Patti Valley (Fig. 6A), a NW-SE trending fault-con-
trolled submarine canyon (see also CuPPari et alii 1999;
Colantoni et alii 2001), where Holocene deposits are de-
formed and locally the seafloor is downthrown of about ∼3 m
(Figs. 6B and C). A right-lateral motion could also character-
ize the VMFZ belt, as suggested by a computed focal mecha-
STRUCTURAL ARCHITECTURE AND ACTIVE DEFORMATION PATTERN IN THE NORTHERN SECTOR OF THE AEOLIAN-TINDARI-LETOJANNI FAULT SYSTEM 15
nism located south-east of the Vulcano island (see Fig. 9C).
Faults are mainly distributed along the eastern slope of the
Patti Ridge where they form a large system running from
the SE flank of the Vulcano Island to SW of Capo Milazzo
(Fig. 6A), roughly following the trend of the Milazzo canyon
and of the adjacent Patti Ridge (Fig. 6A). Vertical displace-
ments observed along these fault segments reach ∼150-200
m and form an impressive fault scarp characterized by dif-
fuse gravitational deformation (Fig. 6D). A NW-SE oriented
horst structure seems to characterize the northern offshore
of the Capo Milazzo peninsula where, based on the seismic
profiles, a recent extensional (or transtensional) regime
seems to occur (Fig. 8), contrary to what was documented by
arGnani et alii, (2007). Indeed, apart the seismological data
(Fig. 9C), the current transtensional significance of the NW-
SE oriented faults detected in the Gulf of Patti would be also
suggested by geodetic data, since 3.6 mm/yr of right lateral
motion along a N126E direction is expected (Palano et alii,
2012).
NNE-SSW to N-S trending extensional faults occur
only in the central sector of the Gulf of Patti (Fig. 6A) where
they form horst and graben association (Fig. 7). This fault
system appears to extend on-land in the Tindari-Barcello-
na depression (see also billi et alii, 2006) where it termi-
nates against the Tindari-Novara fault zone (TNFZ). Here,
a good spatial correspondence between detected faults and
the seismic pattern can be observed. In particular, event lo-
cations (section A-A’ in Fig. 9B) and computed focal mech-
anisms indicate normal faulting along NNE-SSW to NE-
SW oriented rupture nodal planes (Fig. 9C), confirming
the on-land structural observations. In addition, the occur-
rence of NNE-SSW nodal planes (Fig. 9C) could testify the
deep seismogenic activity of the NNE-SSW fault segments
affecting the southern sector of the Gulf of Patti and the
Tindari-Barcellona depression. Besides, the NE-SW orient-
ed nodal planes (Fig. 9C) could suggest the possible deep
seismogenic activity of the NE-SW trending Quaternary
extensional faults outcropping on the whole Peloritani
Mts. sector (Figs. 4A and F).
Taking into account the right-lateral component of mo-
tion of the TNFZ, as suggested by field and geodetic data,
and inferring similar kinematics for the VMFZ (see above),
the Gulf of Patti and the Tindari-Barcellona depression can
be tectonically interpreted as a dilational stepover devel-
oped in the overlapping sector between these two major
right-stepping, en-echelon fault systems (TNFZ and VMFZ,
Fig. 11; see also Cultrera et alii, 2017). The local stress
pattern reorganization in the overlapping area, also testi-
fied by the high values of dilatation strain-rate observed
east to the Tindari GPS station (Fig. 10A), would explain
the occurrence of the minor NNE-SSW oriented normal
faults affecting the Tindari-Barcellona depression and the
southern sector of the Gulf of Patti. Releasing zones and
pull-apart structures are also sites of crustal extension,
significant basin sedimentation, fluid ascent and volcan-
ism (CunninGham & mann, 2007 and references therein), all
characters present along the analyzed sector of the ATLFS
(e.g. fluid and gas vents, Fig. 11).
SEISMOTECTONIC IMPLICATIONS
As suggested by the seismicity pattern and focal mech-
anisms in the northern sector of the ATLFS, seismogen-
ic faulting seems to occur mainly along NW-SE oriented
fault planes and subordinately, along NNE-SSW to NE-SW
oriented ones. Minor reverse faulting mechanisms south
of Salina, east of Lipari and south-west of Vulcano, show
NE-SW to E-W oriented rupture nodal planes (Fig. 9C) and
these could be associated to the eastward migration of the
Sisifo-Alicudi transpressional fault belt (barreCa et alii,
2014). Anyway, in the area of the Lipari-Vulcano complex
the relationships between seismicity and causative faults is
fairly difficult to analyze, because of the possible influence
of the active magmatic processes (e.g. seismicity related to
hydrothermal activity, non-tectonic deformation, see also
ruCh et alii, 2016), of the lack of well oriented earthquakes
clusters (Fig. 9A) as well as the lack of good-quality marine
geophysical data.
As concern the Gulf of Patti, comparing high-precision
earthquakes location and high-resolution seismic reflec-
tion data allowed us to propose a possible link between
detected faults and seismicity. In this sector, although the
structural offset and the bathymetric expression of the
VMFZ (i.e. eastern flank of the Patti Ridge, Milazzo Can-
yon, see Fig, 5) suggest that it could be more active than
the PVFZ, this latter appears to be responsible for most
of the current seismicity occurring in the central sector of
the Gulf of Patti. In fact, the NW-SE oriented PVFZ ap-
pears to be spatially correlated to a fault parallel earth-
quakes cluster west of the Patti Ridge (Fig. 9A, B and
relative foci in Fig. 9C) whose derived focal mechanisms
suggest seismogenic faulting along NW-SE oriented nodal
planes (Fig. 9C). Taking into account that the PVFZ clearly
shows evidence of active deformation in the seismic pro-
files and assuming the shallow faulting (Figs. 6B and C)
as kinematically coherent to the deeper seismogenic one
(mainly distributed from 5 to 15 km of depth, Fig. 8B), the
PVFZ could be interpreted as the shallow expression of a
deeper seismically-active, SW dipping right-transtensional
structure (see section view B-B’ in Fig. 9) developed at the
north-eastern edge of the Gulf of Patti releasing zone.
The main structures of a releasing stepover configu-
ration may also act as barriers to earthquake propagation
(KinG & nabeleK 1985; SibSon 1985; barKa & KadinSKy-Cade
1988) and they can be sites of major earthquakes nuclea-
tion (e.g. Shaw 2006). So, taking into account the distribu-
tion of the largest historical earthquakes occurred in the
investigated area (Fig. 11) and the seismic potential of the
main recognized fault zones (MVFZ, PVFZ, TNFZ), on the
base of empirical fault-length scaling relationships (wellS
& CoPPerSmith, 1994) we argue that the Mw=6.1, 1978 and
the Mw=6.2, 1786 earthquakes (GaSParini et alii, 1982, 1985;
rovida et alii, 2011) have generated along the edges of the
releasing zone, where the major fault zones take place. In
particular, the Mw=6.1, 1978 event could have been gener-
ated along the ~12 km-long PVFZ, at the north-eastern edge
of the releasing zone (Fig. 11), since faults belonging to the
PVFZ clearly show active deformation in the seismic profiles
(see Figs. 6B and C). As regard the Mw=6.2, 1786 event, it
probably nucleated along the northern sector of the TNFZ,
at the south-western edge of the relay area. Moreover, sever-
al archaeological sites nearby seem to have been destroyed
by earthquakes during the first century AD (bottari et alii,
2013). Although active faulting along the TNFZ is not well
imaged by the seismological data (see Fig. 9C), NW-SE ori-
ented faults belonging to this fault zone show geological
and morphological evidence of Holocene activity (see billi
F. CULTRERA ET ALII16
et alii, 2006; de Guidi et alii 2013) and well satisfy the empir-
ical fault-length scaling relationships (wellS & CoPPerSmith,
1994) for generating M~6 earthquakes.
CONCLUSIONS
Field-structural, marine geophysical, geodetic and
seismological data from the northern sector of the ATLFS,
between the Lipari-Vulcano complex (Aeolian Archipel-
ago) and the Peloritani Mts (mainland Sicily) allowed to
better constrain the structural architecture and the active
deformation pattern of this regional belt of deformation.
Our findings confirm the role played by the ATLFS in the
recent geodynamic setting of the SE Tyrrhenian Sea-NE
Sicily area, where it accommodates diverging motions be-
tween distinct blocks located at the southern edge of the
Calabrian Arc (billi et alii, 2006; Palano et alii, 2012; barre-
Ca et alii, 2014; Polonia et alii, 2016).
In particular, the northern sector of the ATLFS consist
of main NW–SE trending, én-echelon arranged, right-tran-
stensional faults and associated NNE-SSW to NE-SW
trending normal faults. The latter structures mainly occur
in the overlapping sectors between the main faults and
form pull apart, and releasing stepovers (Fig. 11). These
secondary tectonic compartments have probably created
the favorable opening conditions for gas, fluid and mag-
ma ascent and are spatially associated to a low-magnitude
seismicity (i.e. southern sector of the Gulf of Patti and the
Tindari-Barcellona depression, Fig. 11).
Fig. 11 - Kinematic reconstruction and structural architecture of the northern sector of the Aeolian-Tindari-Letojanni fault system (ATLFS). This
belt accommodates 3.6 mm/yr of righ-lateral motion between Sicilian and Calabrian blocks (Palano et alii, 2012) and separates a contractional
tectonic compartment, to the west, from an extensional one to the north-east (see inset). As reveled by field and marine geophysical data, the
ATLFS is characterized by “en-echelon” NW-SE trending right-transtensional fault zones (e.g. the main faults of the Lipari-Vulcano islands,
the VMFZ, PVFZ and TNFZ) which in the overlap sectors form pull-apart and releasing stepover structures characterized by remarkable fluids
ascent (see yellow squares; sites from GiammanCo et alii, 2008; barreCa et alii, 2014, this work). Major faults of the releasing stepover may also
act as barriers to earthquake propagation (see density map in the background, from Cultrera et alii, 2017) or conversely, they can be sites of
major earthquakes nucleation.
STRUCTURAL ARCHITECTURE AND ACTIVE DEFORMATION PATTERN IN THE NORTHERN SECTOR OF THE AEOLIAN-TINDARI-LETOJANNI FAULT SYSTEM 17
Although it was not possible to identify seismogenic
faults in the Gulf of Patti, due to the shallow penetration
of our geophysical dataset, most of the structures mapped
offshore show evidence of active deformation as they off-
set Holocene deposits and locally also deform the seafloor.
These faults are interpreted as shallow structures linked to
crustal seismogenic faults. Current and historical seismic-
ity when integrated with our structural model permits to
suggests that moderate earthquakes (1<M<4.6) occur with-
in the releasing zone (see density earthquake map in Fig.
11), whereas major events (e.g. the 1786, Mw=6.2; 1978,
Mw=6,1; rovida et alii, 2011) are roughly aligned with the
major NW-SE oriented bounding faults (VMFZ, PVFZ,
TNFZ).
aCKnowledGementS
The authors gratefully thank the scientific team attending to the
“Milazzo 2013” Cruise and the crew of R⁄V Urania of the National
Council of Researches (CNR) for their helpful support during the ge-
ophysical survey. Francesco Mazzarini and an anonymous reviewer
are gratefully thanked for the accurate and constructive reviews of the
manuscript. This work was partially funded by PRIN 2010–11 Project
“Active and recent geodynamics of Calabrian Arc and accretionary
complex in the Ionian Sea” (responsible C. Monaco).
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Manuscript received 18 August 2016; accepted 13 December 2016; published online 14 December 2016;
editorial responsibility and handling by Laura Crispini
