Late Quaternary slip rates on the Acireale-Piedimonte normal faults and tectonic origin of Mt. Etna (Sicily)

Abstract

Mt. Etna is located along the east coast of Sicily, near the boundary between the continental crust of the Hyblean Plateau and the Mesozoic oceanic crust of the Ionian basin. The main active faults near Mt. Etna cut the base of its eastern flank, forming a 30 km long system of NNE- and NNW-trending, ene´chelon fault segments (the Acireale-Piedimonte system), showing dip-slip and oblique (right-lateral) motion. Most segments are associated with shallow-depth seismicity and all have Late Pleistocene to Holocene vertical slip rates ranging between 1 and 2 mm/yr, typical of major active normal faults worldwide. Eruptive fissures, arranged in NNE- to NE-trending zones, cut the highest slopes of the volcano, on the footwall of the normal fault system. Structural analysis suggests that current motions along both the active faults and eruptive fissures are kinematically compatible and simply linked with ongoing, WNW-ESE-directed regional extension. Such extension characterizes, at a greater scale, the active tectonics of southern Italy, where all large, shallow, historical earthquakes have remained confined within a narrow normal fault belt or rift zone stretching from the northern Calabrian Arc to southeastern Sicily. The southernmost, west-dipping, faults of that rift zone in Calabria (Aspromonte) cut across the Calabro-Peloritan thrust belt to join the mostly east-dipping, Acireale-Piedimonte faults, along the western boundary of Ionian oceanic lithosphere, which continues southwards as the Malta escarpment. We thus relate magmatism at Etna to dilational strain on the footwall of an east-facing, crustal-scale normal fault at the bend where the Siculo-Calabrian rift zone veers ≈ 60° eastwards as it begins to cross the Calabrian Arc, leaving the east-facing margin of the Ionian Sea, to catch up with the west-facing margin of the Tyrrhenian Sea farther north.