Abstract
Offshore data in the western Ionian Sea indicate that the NW–SE-trending dextral shear zone of the Alfeo-Etna Fault System turns to the N–S direction near the Ionian coastline, where the extensional Timpe Fault System is located. Morpho-structural data show that NW–SE-trending right-lateral strike-slip faults connect the Timpe Fault System with the upper slope of the volcano, where the eruptive activity mainly occurs along the N–S to NE–SW-trending fissures. Fault systems are related to the ~E–W-trending extension and they are seismically active having given rise to shallow and low-moderate magnitude earthquakes in the last 150 years. As a whole, morpho-structural, geodetic and seismological data, seismic profiles and bathymetric maps suggest that similar geometric and kinematic features characterize the shear zone both on the eastern flank of the volcano and in the Ionian offshore. The Alfeo-Etna Fault System probably represents a major kinematic boundary in the western Ionian Sea associated with the Africa–Europe plate convergence since it accommodates, by right-lateral kinematics, the differential motion of adjacent western Ionian compartments. Along this major tectonic alignment, crustal structures such as releasing bends, pull-apart basins and extensional horsetails occur both offshore and on-land, where they probably represent the pathway for magma uprising from depth.
Highlights
Since the Middle Pleistocene, contractional structures related to the approximately NNW–SSE compressive regional tectonic regime at the collisional front [31,32] have been coupled with oblique transtensional faults across the western Ionian Basin. These faults form a lithospheric boundary characterized by strong seismicity and active volcanism, which extends from the Aeolian Islands, at the south-western edge of the Ionian subduction system [12,33,34], to the offshore of eastern Sicily, including the NW–SE-trending Ionian fault and Alfeo-Etna fault systems (Figure 1; [9] and reference therein)
Etna, crossed by the extensional NNW–SSE to N–Strending Timpe Fault System and by NW–SE-oriented strike-slip and oblique structures (Figure 2), is the most tectonically active area of the volcanic edifice both for the number of volcano-tectonic seismic events and for the maximum intensity reached at the epicentre [38]
Unlike the western sector of the volcano, where seismicity occurs at greater depths related to the regional NNW–SSE-oriented compression [28,39,40], on the eastern sector the intense tectonic activity of the Timpe Fault System is characterized by several shallow earthquakes with a mediumlow magnitude
Summary
Since the Middle Pleistocene, contractional structures related to the approximately NNW–SSE compressive regional tectonic regime at the collisional front [31,32] have been coupled with oblique transtensional faults across the western Ionian Basin These faults form a lithospheric boundary characterized by strong seismicity and active volcanism, which extends from the Aeolian Islands, at the south-western edge of the Ionian subduction system [12,33,34], to the offshore of eastern Sicily, including the NW–SE-trending Ionian fault and Alfeo-Etna fault systems (Figure 1; [9] and reference therein). The eastern lower slope of Mt. Etna, crossed by the extensional NNW–SSE to N–Strending Timpe Fault System and by NW–SE-oriented strike-slip and oblique structures (Figure 2), is the most tectonically active area of the volcanic edifice both for the number of volcano-tectonic seismic events and for the maximum intensity reached at the epicentre [38]. Uplifted paleo-shorelines at the footwall of normal faults, documented at the SE sector of the volcano [55], suggest that, in the long-term, the tectonic signal prevails over the gravitational signal
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