The differing behaviour of the eastern and western flanks of Mount Etna has been investigated by analyzing morphological, structural, volcanic and seismic data. Morphological and structural analyses have pointed out a higher "degree" of tectonization on the eastern side. From the volcanological point of view, the analysis of some parameters of adventive eruptions during the last three centuries did not evidence great differences between the two sides of the volcano. Only higher lava outputs on the eastern flank have been remarked. Historic and recent seismic activity has been analyzed for the number and magnitude of events, strain energy release and frequency-magnitude law. The shallowest and strongest earthquakes occur on the eastern side of the volcano, strictly linked to a regional structural system trending NNW-SSE. The western side is mostly characterized by deeper earthquakes that seem to control the volcanic activity. Lower seismic energy releases and higher values of the b coefficient in the Gutenberg-Richter's (1956) law can be observed on the western side. The differences observed between the two sides of the volcano have been interpreted in terms of both regional and local tectonics, with the result that a higher extensional stress field is attributed to the eastern side of the volcano. © 1990.
