Ground-Motion Simulations for the 1980 M 6.9 Irpinia Earthquake (Southern Italy) and Scenario Events

Abstract

In this paper, we adopt three ground-motion simulation techniques (the stochastic finite-fault simulation code from Motazedian and Atkinson, 2005; the hybrid deterministic-stochastic approach with approximated Green's functions from Pacor et al., 2005; and the broadband hybrid integral-composite technique with full-wavefield Green's functions from Gallovic and Brokesova, 2007), with the aim of investigating the different performances in near-fault strong-motion modeling andpredictionfrompastandfutureevents.Thetestcaseisthe1980M6.9Irpiniaearth- quake, the strongest event recorded in Italy in the last 30 years. First, we simulate the recorded strong-motion data and validate the model parameters by computing spectral accelerationandpeakamplituderesidualdistributions.Thevalidatedmodelisthenused to investigate the influence of site effects and to compute synthetic ground motions around the fault. Afterward, we simulate the expected ground motions from scenario events on the Irpinia fault, varying the hypocenters, the rupture velocities, and the slip distributions. We compare the median ground motions and related standard deviations from all scenario events with empirical ground-motion prediction equations (GMPEs). The synthetic median values are included in the median 1 standard deviation of the considered GMPEs. Synthetic peak ground accelerations show median values smaller and with a faster decay with distance than the empirical ones. The synthetics total stan- dard deviation is of the same order or smaller than the empirical one, and it shows considerable differences from one simulation technique to another. We decomposed the total standard deviation into its between-scenario and within-scenario components. The larger contribution to the total sigma comes from the latter, while the former is found to be smaller and in good agreement with empirical interevent variability. Online Material: Comparison of observed and simulated waveforms and spectra.