Ground Motion Earthquake Scenario Parameters For The 2009 Abruzzo Earthquake

Abstract

The evaluation of the seismic action, which the structures must withstand, is the most critical item of the full process of analysis, monitoring and mitigation of seismic risk. Seismic action has been recorded worldwide for moderate to severe earthquakes. In the last 30 years the recorded accelerations have been significantly increased. One reason could be the increasing number of recording stations and the location of many such stations on soft soil, where significant site amplification can occur. In many cases, the recorded accelerations have exceeded the designed acceleration given by seismic codes. This is particularly true in the case of a strong earthquake, when the evaluation of seismic action given by source mechanism results, in some cases, in a seismic design earthquake greater than that given by the probabilistic evaluation reported by the codes. Also in the case of the moderate ML = 5.8 Abruzzo earthquake, the recorded acceleration exceeded the provisions given by Italian Code. Mainly two factors could explain that. One factor is related to the different results obtained by the probabilistic evaluation of seismic action given by the codes and the deterministic seismic action evaluated by source modelling of the scenario earthquake. The second factor is related to the role of site amplification, which is higher for small to moderate earthquakes and lower for severe scenario earthquakes. These two factors are discussed for the case of the Abruzzo 2009 earthquake where, because of the normal fault mechanism, severe vertical components of the acceleration were recorded; also significant site effects occurred, particularly in the Aterno valley.