Abstract

A paleoseismological investigation has been recently undertaken along the Moscarello fault, one of the most outstanding tectonic feature of the Timpe fault system in the Mt. Etna volcano eastern flank. Such a tectonic structure, showing extensional kinematics, is highly active as revealed both by geomorphological features and by seismicity data. Volcano-related seismicity in the last ca. 150 years is typically characterised by very frequent, shallow (H<5 km) and moderate magnitude (M<4.8) earthquakes producing macroseismic intensities up to the X grade MSK in narrow zones around the fault trace, including extensive surface faulting (end-to-end rupture length up to 6 km, vertical offsets up to 90 cm). Two trenches have been carried out along the central sector of the fault that borders a small Holocene sedimentary basin (Fondo Macchia). This sector of the fault ruptured coseismically 4 times since 1855, and is characterized by the lack of aseismic creep. Trench A is located where eye-witnesses observed a coseismic scarp of ca. 20 cm following the April 1971 event. The footwall stratigraphy revealed an alluvial deposit and radiocarbon dating yielded calibrated ages of 6,250-3,250 years B.P. In the hangingwall, not-stratified colluvial deposits were exposed; radiocarbon dating and archaeological data indicate ages in the range between 3,470 years B.P. and the present. Using the exposed sections, a hand-dug borehole and a Standard Penetration Test we reconstructed a cumulative vertical offset of at least 5.6 m. The relations between the depositional/erosional surfaces and the geometry of the fault planes in this trench indicate several events of reactivation of the fault scarp connected to repeated earthquakes. Trench B displayed deposits which can be correlated with those of the trench A, and provided a better definition of depositional processes and chronology in the trench area. Trench data obtained for this sector of the Moscarello fault indicate a vertical slip rate between 2 and 4 mm/yr during the latest Holocene. Such a deformation rate is clearly much higher than that obtained for active, capable normal faults along the Apennine Chain (from 0.1 to 1 mm/yr). These findings show that paleoseismological investigations may be considered as an useful tool for long-term analysis of Holocene active faults and related hazards also in volcanic areas.

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