Broadband (up to 5 Hz) dynamic rupture modeling with fractal fault roughness and topography: the 2016 Mw 6.2 Amatrice, Italy earthquake

Physics-based earthquake simulations help to better constrain ground motion amplitudes and variability in seismic hazard applications. At the same time, recorded strong ground motions can be utilized in dynamic source inversions to infer the dynamic parameters governing how faults yield and slide, such as fault friction parameters and stress conditions (Gallovic et al., 2019a,b). However, at high frequencies, simulations and inversion of earthquake ground motions are computationally and methodologically challenging. We here present 3D broadband dynamic rupture models of the 2016 Mw 6.2 Amatrice, Italy earthquake. Our starting point is best-fitting heterogeneous fault stresses and friction parameters resulting from Bayesian dynamic rupture inversion of 20 three-component strong-motion waveforms recorded within 50 km from the fault limited to frequencies up to 0.5-1 Hz, a simple planar fault geometry, and omitting topography effects. We extend this model to the broadband (up to 5 Hz) regime by incorporating high-resolution topography, viscoelastic attenuation, and a geometrically complex rough fault interface with a band-limited self-similar (H=1) profile and roughness amplitude ratio of 10-2. We show that realistic high-frequency radiation can be recovered by combining small-scale fractal fault roughness, randomly heterogeneous Dc, a scalar correction to the Bayesian initial stress conditions for the additional roughness drag and increased nucleation energy. Specifically, our model demonstrates a good match with actual data regarding velocity-acceleration waveforms and Fourier amplitude spectrums (FAS) up to 5 Hz at stations with weak site effects while highlighting the importance of fully dynamic modeling of non-linear source-path-site effects in future simulations.