Aspetti geomorfologici e sismologici connessi a fenomeni di tettonica gravitativa nel basso versante orientale dell'Etna

Abstract

The lower eastern flank of Mt. Etna Volcano is interested by earthquakes with superficial foci and by aseismic creeps. The main morphogenetic factor depends from local tectonic structures (which are controlled by regional faults) and by volcanic activity. These local faults form morphological complex scarps (locally named 'timpe' with a remarkable vertical development, or rectilinear flexures (fault escarpments covered by lava flows). During the last 200 years, earthquakes 28 Io > VII MSK which were recorded in the area among Acireale, Santa Venerina and Giarre (Catania district); all these earthquakes have hypocentres less deep than 2 km. From bibliographic data it can be seen that soil fractures with vertical displacement up to 70 cm and horizontal ones between few mm and some cm have been recorded for every earthquake. Some faults show slow aseismic creeps, measured between 0.2 and 1 cm/y. This slow local lowering, in the frame of a general uprising of Etnean region, caused coastal withdrawal. Data coming from the studies are allow to describe the whole phenomena concerning the lower Eastern flank of Mt. Etna as 'multiple retrogressive slide'. These phenomena are caused by a ductile clayey substratum, located below a volcanic and sedimentary cover with brittle behaviour. These dislocations are located in a very populated region, and cause problems regarding existing buildings and urbanistic choices. Furthermore, the open fractures may pollute the underground water, if there is any pollution activity.