2016–17 Central Italy Earthquake Sequence: Seismic Retrofit Policy and Effectiveness

The 2016–17 Central Italy Earthquake Sequence consisted of several moderately-high magnitude earthquakes, between Moment Magnitude M5.5 and M6.5, each centered in a different location and with its own sequences of aftershocks, spanning several months. To study the effects of this earthquake sequence on the built environment and the impact on the communities, a collaborative reconnaissance effort was organized by the Earthquake Engineering Research Institute (EERI), Eucentre Foundation, European Centre for Training and Research in Earthquake Engineering (EUCentre), and the Rete dei Laboratori Universitari di Ingegneria Sismica (ReLuis). The effort consisted of two reconnaissance missions: one following the Amatrice Earthquake of August 24th 2016, and one after the end of the earthquake sequence, in May 2017. One objective of the reconnaissance effort was to evaluate existing strengthening methodologies and assess their effectiveness in mitigating the damaging effects of ground shaking. Parallel studies by the Geotechnical Extreme Events Reconnaissance (GEER) Association, presented in a companion paper, have demonstrated that variations in ground motions due to topographic site effects had a significant impact on damage distribution in the affected area. This paper will present that, in addition to these ground-motion variations, the variation in vulnerability of residential and critical facilities was observed to have a significant impact on the level of damage observed in the region. The damage to the historical centers of Amatrice and Norcia will be used in this evaluation: the historical center of Amatrice was devastated by the sequence of earthquakes, while the significant damage in Norcia was localized to individual buildings. Amatrice has not experienced the same number of devastating earthquakes as Norcia in the last 150 years. As a result, its building stock is much older than that of Norcia and there appeared to be little visual evidence of strengthening of the buildings. The distribution of damage observed throughout the region was found to be indicative of the effectiveness of strengthening and of the need for a comprehensive implementation of retrofit policies.