Some seismologieal results and geostructural suggestions from a study of the Reggio Calabria earthquake of 16 January, 1975

Starting from the analytic determination of the most important parameters of the Reggio Calabria earthquake, several geostructural hypotheses are analyzed and discussed. The statistical hvpocentre, calculated in two separate phases for (lie epicentral coordinates (q> = 38°04'28"; A = 15°38'55") and for the depth (h = 10.04 km), is consistent with an earlier macroseismic estimation. The travel times for the first arrivals, limited to the distance interval 0 ^ ¿1° ^ 12 can be approximated by means of the three linear equations: which can be interpreted as the travel-time curves of the direct (Pg) and refracted (Pn i , P„2) longitudinal waves. The existence of a focal mechanism, compatible with a couple + oppositely directed force model is deduced from a study of the signs of the first impulses. This model includes faulting and displacement with dislocation plane N 22"K and inclination of ~ 75° towards XI 12°E. Considering the focal location and our geostructural knowledge of the area involved, the Reggio Calabria earthquake can be explained by a process of tectonic distension due to the drift of the Calabrian Arc and to other reliable geostructural elements. The explanation is critically evaluated in relation to the tectonic forces involving the Strait of Messina and the volcanic zone of Etna