CARATTERISTICHE GEOLOGICO-GEOMORFOLOGICHE ED EFFETTI DI SITO A SAN GIULIANO DI PUGLIA (CB) E IN ALTRI ABITATI COLPITI DALLA SEQUENZA SISMICA DELL’OTTOBRE-NOVEMBRE 2002

Abstract

Giaccio B. (et al.), Geological-geomorphological characteristics and site effects at San Giuliano di Puglia (Molise,
Southern Italy) and other localities struck by the seismic sequence of October-November 2002. IT ISSN 0394-3356, 2004.
On October 31 and November 1 2002, the eastern Molise region (Biferno and Fortore rivers) of the southern Apennines (southern Italy) was struck by two seismic events characterised by magnitude ML 5.4 and 5.3, respectively. Although the magnitude is definitely lower than that of the largest Apennine seismic events (ML>6), in some villages the earthquake caused significant damage, particularly at San Giuliano di Puglia. Preliminary surveys at the damaged localities revealed strong differences in the damage distribution. In some villages, indeed, we observed the coexistence of areas characterised by significant damage (with partial or total collapse of edifices) with areas affected by little damage. The highest intensity of 8-9 MCS has been assigned to San Giuliano di Puglia, while intensities of 7 and 6-7 MCS have been attributed to Bonefro and Colletorto (located close to San Giuliano di Puglia), respectively. Intensities of 7-8 and 8 MCS have in no case been attributed. These anomalies suggested that local effects, e.g. related to peculiar geologic and morphologic conditions or landsliding, may have played an important role in determining the damage distribution. This role may have been amplified by the characteristics and age of the edifices, significantly different throughout a single village. In order to asses the site effects at San Giuliano di Puglia, Ripabottoni, Morrone del Sannio, Pietramontecorvino and Castellino del Biferno, a multidisciplinary geological investigation (stratigraphy, biostratigraphy, structural geology and geomorphology) was performed. Such a multidisciplinary approach has allowed an assessment of the contribution that the single local factor(s) eventually had in determining the damage amplification. The detailed geological studies carried out at San Giuliano di Puglia permitted the definition of the main stratigraphic and structural features of this area, conditioned by a complicated structural style, with thrusts and folds affecting the Toppo Capuana and Flysch di Faeto Formations (Tortonian and Langhian-Tortonian, respectively). The comparison of the damage distribution with the structural framework permits the definition of a direct relationship between the maximum damage and the foundation of the buildings in the clayey marls of the Toppo Capuana Formation. In contrast, the edifices founded in the marly limestone of the Flysch di Faeto Formation suffered less severe damage. In the other investigated localities, the site effects seem more moderate. The slight damage amplification is mainly due to the coseismic re-activation of pre-existing landslides