Tilting variations and seisruieity that preceded the strong Friuli earthquake of May 6th, 1976

Abstract

In a long 1970 work on the seismic and geodynamic characteristics<br />of the Po Valley (to be understood in the broadest sense,<br />that is, as including the Adriatic-Po, trough and all the beds and<br />basins of the rivers emptying into the upper Adriatic as well as the<br />mountains bordering it), Caloi et al observed, in commenting an the<br />diagram of seismic energies in recent centuries up to 1969, with particular<br />reference to the last century, that:<br />"It began with the strong earthquake of Santa Croce in 1875,<br />which suddenly broke the relative seismic quiet that had endured<br />throughout the broad zone since 1800. The disastrous seismic crisis<br />of the Lake Santa Croce zone was followed that same year by strong<br />seismic activity on the opposite side of the plain, at Cattolica near<br />the sea, along the northern Appennine slopes. It almost seems that<br />these violent ruptures of the seismic equilibrium on the two sides of the<br />plain were linked as cause and effect, and vice versa. The same phenomenon<br />occurred at other times during the past century: the strong<br />Adriatic earthquake of 1934 (Caloi, 1937) ('), for example, was followed<br />two years later by the very strong earthquake of Cansiglio (Caloi,<br />1938)