The May 1976 friuli earthquake (Northeastern Italy) and interpretations of past and future seismicity

Abstract

(Accepted for publication June 8, 1978) ABSTRACT: Rogers, T.H. and Cluff, L.S., 1979. The May 1976 Friuli earthquake (Northeastern Italy) and interpretations of past and future seismicity. In: C.A. Whitten, R. Green and B.K. Meade (Editors), Recent Crustal Movements, 1977. Tectonophysics, 52: 521-532. The May 6, 1976 Friuli earthquake (surface wave magnitude 6.3; intensity VII—X, Mercalli—Sieberg scale) was one of the strongest earthquakes ever felt in south-central Europe. Seismologic and geologic data have indicated: (1) the fault rupture causing the earthquake most probably occurred within a fault zone striking E—NE, and dips gently N—NW under the Venetian Alps; and (2) the principal fault displacement was most probably thrust on the northward-dipping plane. In recent years, many authors have proposed plate tectonic models for the Mediterranean region. A new variation on previously proposed models is postulated to form a basis for interpreting the Friuli earthquake and other northern Italy historical earthquakes. This model postulates an “Adriatic” microplate having a norhtern boundary that, in part, extends along the NE-trending front of the Venetian Alps. Relative motion of the Adriatic microplate northward and under the European megaplate is believed to be a reasonable explanation of the Friuli earthquake. Based on known geologic and seismologic data, the northern boundary of the Adriatic microplate is interpreted to extend westward in an irregular manner through the central part of the Po Valley. Major earthquakes in the Po Valley have occurred along linear trends subparallel to the valley during the period between A.D. 1001 and 1781. These major earthquakes are possibly related to past motion of the Adriatic microplate, occurring along either microplate boundaries or intraplate zones related to movement along microplate boundaries. Future seismicity is anticipated, based on these data and interpretations, and current and future siting studies for major critical facilities in northern Italy and south-central Europe should consider these factors. For instance, in the selection of design earthquakes and the evaluation of surface-faulting potential, available geologic and seismologic data should be reevaluated. Additional investigations should be conducted to gain a greater understanding of the tectonic processes involved and their evolution as imprinted in the Late Cenozoic geologic record.