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

In a long 1970 work on the seismic and geodynamic characteristicsof the Po Valley (to be understood in the broadest sense,that is, as including the Adriatic-Po, trough and all the beds andbasins of the rivers emptying into the upper Adriatic as well as themountains bordering it), Caloi et al observed, in commenting an thediagram of seismic energies in recent centuries up to 1969, with particularreference to the last century, that:"It began with the strong earthquake of Santa Croce in 1875,which suddenly broke the relative seismic quiet that had enduredthroughout the broad zone since 1800. The disastrous seismic crisisof the Lake Santa Croce zone was followed that same year by strongseismic activity on the opposite side of the plain, at Cattolica nearthe sea, along the northern Appennine slopes. It almost seems thatthese violent ruptures of the seismic equilibrium on the two sides of theplain were linked as cause and effect, and vice versa. The same phenomenonoccurred at other times during the past century: the strongAdriatic earthquake of 1934 (Caloi, 1937) ('), for example, was followedtwo years later by the very strong earthquake of Cansiglio (Caloi,1938)