Investigation of pre-1700 Earthquakes Between the Adda and the Middle Adige River Basins (Southern Alps)

Abstract

While the seismicity of the Southern Alps is high in the Eastern sector, corresponding to the Veneto and Friuli regions, it decreases towards West up to the Adda River. In the sector between the Lessini Mts. and Eastern Friuli the damaging earthquakes are clustered in a well defined seismic belt, where seismogenic sources responsible for earthquakes with Mw 6 have been defined in recent works. In contrast, the knowledge of the Southalpine sector West of this area is sparser; the area experienced some earthquakes with Mw>5.5 and varied events with 4.8≤Mw≤5.5 the distribution of which is, apparently, random. For the area roughly defined by the basins of the Adda River to the West and the middle Adige River to the East, this paper reappraises the background knowledge of the earthquakes occurred before 1700. The investigation and the results are presented according to two successive periods, up to 1995 and from 1995 on. In the research performed up to 1995, the most important achievements concerned two different aspects: i) the assessement of several “fake quakes”, some of which were the object of paradigmatic case-histories; ii) the resizing and relocation of several, presumed damaging earthquakes. Though this round of investigation changed significantly the picture of the seismicity with respect to the Seventies, the research continued. For the period from 1995 on, the discussion focuses on the reliability of the available information; material that received little or no consideration before, new historical findings and comments to the seismological interpretation as in the most recent literature are also presented. This part includes also the discussion of archaeoseismological evidence of damage related to past earthquakes.