PREdiction of NOn-LINear soil behavior (PRENOLIN) is an international benchmark aiming to test multiple numerical simulation codes that are capable of predicting nonlinear seismic site response with various constitutive models. One of the objectives of this project is the assessment of the uncertainties associated with nonlinear simulation of 1D site effects. A first verification phase (i.e., comparison between numerical codes on simple idealistic cases) will be followed by a validation phase, comparing the predictions of such numerical estimations with actual strongmotion recordings obtained at well-known sites. The benchmark presently involves 21 teams and 23 different computational codes.We present here the main results of the verification phase dealing with simple cases. Three different idealized soil profiles were tested over a wide range of shear strains with different input motions and different boundary conditions at the sediment/bedrock interface. A first iteration focusing on the elastic and viscoelastic cases was proved to be useful to ensure a common understanding and to identify numerical issues before pursuing the nonlinear modeling. Besides minor mistakes in the implementation of input parameters and output units, the initial discrepancies between the numerical results can be attributed to (1) different understanding of the expression "input motion" in different communities, and (2) different implementations of material damping and possible numerical energy dissipation. The second round of computations thus allowed a convergence of all teams to the Haskell-Thomson analytical solution in elastic and viscoelastic cases. For nonlinear computations, we investigate the epistemic uncertainties related only to wave propagation modeling using different nonlinear constitutive models. Such epistemic uncertainties are shown to increase with the strain level and to reach values around 0.2 (log 10 scale) for a peak ground acceleration of 5 m=s 2 at the base of the soil column, which may be reduced by almost 50% when the various constitutive models used the same shear strength and damping implementation.

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The development of a soil shear rupture during an earthquake can occur along unstable slopes and at\ud the foundation level, for sliding failure mechanisms. This singularity in the seismic wave propagation is\ud not implemented in the common codes for one-dimensional seismic response analysis, usually including\ud linear equivalent soil models. Instead, the code developed in this study was conceived, addressed and\ud optimised to reliably model both the ‘transient’ seismic response (‘stick’ mode) and the permanent\ud deformation mechanisms accounting for the coupled effects of deformability and strength (‘slip’ mode).\ud The code models the soil profile as a system of consistent lumped masses, connected by viscous\ud dampers and springs with hysteretic non-linear behaviour. The viscous damping matrix is defined\ud according to the Rayleigh formulation. The non-linear hysteretic soil response is described by the MKZ\ud model and modified Masing rules. The shear failure is modelled through plastic sliders activating when\ud the limit shear strength is reached. The code is applied to model the behaviour of an earth dam and a\ud natural slope that have undergone significant displacements during strong-motion earthquakes; the\ud results are compared with the observations and those obtained by uncoupling the seismic response from\ud the displacement analysis by the rigid sliding block model

The central Italy earthquake sequence has, to date, generated three mainshocks:M6.1 24 August, M5.9 26 October, and M6.5 30 October 2016. These events, along with aftershocks, were well recorded by Italian networks, and are among the normal fault earthquakes with the highest number of recordings globally. We process records for six events using NGA/PEER procedures. Many recording sites lacked VS30 assignments, which we provide using measured shear wave velocity profiles where available and a local geology proxy otherwise. Stations at close distance, including near the hanging wall, exhibit fling step in some cases but no obvious rupture directivity. The data exhibit fast anelastic attenuation at large distances (>100 km), as predicted by recent Italy-adjusted global models, but not by Italyspecific models. We partition residuals from Italy-adjusted global models, finding negative event terms at short periods (weaker than average shaking). We apply Kriging of within-event peak acceleration and velocity residuals using a global semi-variogram model to estimate the spatial distribution of peak accelerations, which are generally most intense south-west of Mt. Vettore.