L’analisi statistica di quindici insiemi di misure di rilassamento di sforzo elastico in quindici differenti insiemi di terremoti (sequenze, sciami, scosse successive o terremoti scelti a caso in una regione) per un totale di 926 eventi in Italia, Giappone, Isole Aleutine, Messico e California, conferma che il rilassamento di sforzo $p$ è una funzione decrescente di $p$ ed è quasi proporzionale a $p^{x-1}$$(a < o)$ come previsto da Caputo (1976). Usando questa distribuzione statistica e quella delle dimensioni lineari delle faglie, si introduce una nuova formula per il periodo di ritorno $n(a)$ della radice dell'accelerazione quadratica media maggiore di $a$ causata dai terremoti di una regione sismica ad una distanza $R$; si trova che $n(a)$ è quasi proporzionale a $(\bf{R}^{3/2}a)^{-\delta}$$(\delta = 3.5)$.
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Con il contributo del Ministero per i Beni e le Attività Culturali