Broadband Ground Motion Simulations in the Messina Strait Area (Southern Italy): Appraising Strong Motion Variability due to Complexity in Source and Earth Structure.

Strong ground motion variability due to source complexity and heterogeneous Earth structure has been the subject of a large number of studies. As widely recognized, this variability is particularly evident in near-field ground motion complexity, but also present in high-frequency far-field recordings. To study more quantitatively the effects of source and medium complexity on near-field ground motions, we carry out a numerical experiment, considering physics-based earthquake rupture models and different 1D crustal velocity models. Focusing on the Messina Strait area, struck by a devastating large earthquake (M 7.1) one century ago, we calculate broadband (0-10 Hz) seismograms by combining full waveform low-frequency (0- 3.5 Hz) synthetics and physics-based stochastic high-frequency seismograms (Mai and Olsen, 2008). From recently published studies of the area, we select three representative crustal models and address the influence of Green's functions variability on ground-shaking levels. Simultaneously, we also consider physics- based source models using the pseudo-dynamic approximation to dynamic rupture (Guatteri et al., 2004). This approach allows slip, rise-time and rupture velocity to vary over the fault plane consistent with rupture dynamics, incorporating also constraints on the hypocenter location (Mai et al., 2005). We validate our simulations by comparing common ground motion parameters (peak ground displacement, peak ground velocity, peak ground acceleration and spectral acceleration) with the recent "next generation" (NGA) ground motion prediction equations. Our work furnishes realistic strong motion time series for future earthquakes, adoptable for engineering design purposes, but highlights also their variability due to physics-based source characteristics and different crustal models.