Experimental and Numerical Results on Earthquake-Induced Rotational Ground Motions

Stimulated by the lack of direct measurements of earthquake-induced ground rotations, a set of experimental and numerical results on rotational ground motion is illustrated. The results cover a relatively broad range of magnitude (4–6.5), and regard both far field and near source conditions. Experimentally, results are derived through a suitable spatial interpolation procedure of displacement records collected from two dense arrays, Parkway Valley (New Zealand) and UPSAR (California). Validation checks both with other array-derived methods and with numerical simulations are carried out, to verify the reliability of our estimations and the capability of numerical wave propagation analysis codes to provide realistic estimates of rotational ground motions over a reasonable frequency band. Peak Ground Velocity (PGV) and Peak Ground Rotation (PGR) values obtained via the spatial interpolation procedure over dense seismic arrays are then put in comparison with the numerical results computed along two representative cross-sections of the Grenoble Valley (France), in the near field of a MW 6 strike-slip fault. In this case, a combination of topographic, rupture directivity, and site effects produces rotations of remarkable amplitudes, of the order of 10-3 rad. Finally, PGV-PGR values resulting from both the experimental procedure and the numerical simulations are discussed. A common linear trend between PGV and PGR is found and turns out to be in reasonable agreement with other published results.