Prediction of ground-motion parameters for the volcanic area of Mount Etna

Abstract

Ground motion prediction equations (GMPEs) have been derived for peak ground acceleration (PGA), velocity (PGV) and 5%-damped spectral acceleration (SA) at frequencies between 0.1 and 10 Hz for the volcanic area of Mt. Etna. The dataset consists of 91 earthquakes with magnitudes 3.0<ML<4.8 and epicentral distances between 0.5 km and 100 km. Given the specific characteristics of the area, we divided our data set into two groups: Shallow Events (SE, focal depth < 5 km), and Deep Events (DE, focal depth > 5 km). Signals of DE typically have more high frequencies than those of SE. This difference is clearly reflected in the empirical GMPEs of the two event groups. Empirical GMPEs were estimated considering several functional forms: Sabetta and Pugliese (1987) (SP87), Ambraseys et al. (1996) (AMB96), and Boore and Atkinson (2008) (BA2008). From ANOVA we learn that most of the errors in our GMPEs can be attributed to unmodelled site effects, whereas errors related to event parameters are limited. For DE, BA2008 outperforms the simpler models SP87 or AMB96. For SE, the simple SP87 is preferable considering the Bayesian Information Criterion since it proves more stable with respect to confidence and gives very similar or even lower prediction errors during cross-validation than the BA2008 model. We compared our results to relationships derived for Italy (ITA10, Bindi et al. 2011). For SE, the main differences are observed for distances greater than about 5 km for both horizontal and vertical PGAs. Conversely, for DE the ITA10 heavily overestimates the peak ground parameters for short distances.