Seismic hazard in Central Italy and the 2016 Amatrice earthquake

Carlo Meletti Carlo Meletti,Francesco Visini Francesco Visini,Vera D'amico Vera D'Amico,Andrea Rovida Andrea Rovida

doi:10.4401/ag-7248

Abstract

The Amatrice earthquake of August 24th, 2016 (Mw 6.0) struck an area that in the national reference seismic hazard model (MPS04) is characterized by expected horizontal peak ground acceleration (PGA) with 10% probability of exceedance in 50 years higher than 0.25 g. After the occurrence of moderate-to-large magnitude earthquakes with a strong impact on the population, such as the L’Aquila 2009 and Emilia 2012 ones (Mw 6.1 and 5.9, respectively), possible underestimations of the seismic hazard by MPS04 were investigated, in order to analyze and evaluate the possible need for its update. One of the most common misunderstanding is to compare recorded PGA only with PGA with 10% probability of exceedance in 50 years. Moreover, by definition, probabilistic models cannot be validated (or rejected) on the basis of a single event. However, comparisons of forecasted shakings with observed data are useful for understating the consistency of the model. It is then worth highlighting the importance of these comparisons. In fact, MPS04 is the basis for the current Italian building code to provide the effective design procedures and, thus, any modification to the seismic hazard would also affect the building code.In this paper, comparisons between recorded ground motion during the Amatrice earthquake and seismic hazard estimates are performed, showing that the observed accelerations are consistent with the values expected by the MPS04 model.

Highlights

Since 2006 Italy has a reference seismic hazard model in accordance with the Prime Minister Ordinance 3519/2006, which ratified the MPS04 (Mappa di Pericolosità Sismica 2004) seismic hazard model [MPS Working Group, 2004; Stucchi et al, 2011; http://zonesismiche.mi.ingv.it/] as the basic elaboration to be considered to update the seismic classification of municipalities
A comparison between available recordings for the 24 August 2016 Amatrice earthquake and expected accelerations provided by the reference seismic hazard model (MPS04) for Italy was performed
In order to understand possible reasons for the “failure” of the MPS04 model at accelerometric station (AMT) station, we investigated the impact of the adoption of different ground-motion predictive equations (GMPE) on probabilistic seismic hazard (PSH) assessment

Summary

INTRODUCTION

Since 2006 Italy has a reference seismic hazard model in accordance with the Prime Minister Ordinance 3519/2006, which ratified the MPS04 (Mappa di Pericolosità Sismica 2004) seismic hazard model [MPS Working Group, 2004; Stucchi et al, 2011; http://zonesismiche.mi.ingv.it/] as the basic elaboration to be considered to update the seismic classification of municipalities. The 24 August 2016 Amatrice (Central Italy) Mw 6.0 earthquake occurred in an area with the highest seismic hazard in Italy, where the PGA values expected with a probability of exceedance of 10% in 50 years are higher than 0.25 g (Fig. 1). The Amatrice event struck a region that, in the ZS9 seismic source model, belongs to a large area source [ZS923], characterized by prevalent normal faulting focal mechanisms and a maximum magnitude of 7.2, and where a number of strong earthquakes occurred in the past (Fig. 2), including the 2009 Mw 6.1 L’Aquila event. This paper is focused on the 24 August Mw 6.0 earthquake and does not take into account the following large events of 26 and 30 October 2016 (Mw 5.9 and 6.5, respectively)

SEISMIC HAZARD AND GROUND-MOTION RECORDINGS OF THE AMATRICE

Findings

CONCLUSIONS