Near‐Source Ground Motion From Normal Faults: Insights From the Physics‐Based Numerical Simulations of the 1980 Irpinia Earthquake, Southern Italy

In this paper, the physics‐based numerical simulation of the strongest instrumental earthquake in the recent seismic history of Italy, i.e., the Nov 23, 1980 Irpinia earthquake in Southern Italy, with magnitude M W 6.8, is presented and discussed. A 3D spectral element model covering an extended region (147 × 110 km 2 ) was constructed, with a frequency resolution up to 2 Hz, encompassing a rather complex multi‐segment kinematic fault rupture model and a crustal velocity model including the ground topography. Although a strict validation of the numerical model is not possible, owing to the limited data available for this historical earthquake, simulations are found to capture the main features of the spatial and temporal variability of ground motion realistically, as testified by the quantitative comparison with the available recordings and with the macroseismic intensity observations. The results are investigated to gain insights into the key features of near‐source ground motion during normal‐fault earthquakes, including the spatial variability of the permanent ground deformation field, as well as amplitude, period content, azimuth, and polarization (fault normal vs. fault parallel) of pulse‐like signals caused by up‐dip directivity effects.