BENTO: A Benchmark on 3D Numerical Simulations for Evaluating the Impact of Topography on Ground Motion

3D numerical simulations are widely used to evaluate the impact of topography on ground motion in both homogeneous and heterogeneous media. To ensure consistency among different simulation methods in predicting ground motion amplification and de-amplification on topographic sites, the “BEnchmark of 3D Numerical Simulations on TOpographic Sites” (BENTO) was launched. Partially funded by the Cashima-3 and Sigma-3 research programs, BENTO started in September 2024 and will run until fall 2026, with results to be presented at the ESG 2026 conference in Grenoble, France. The benchmark brings together 20 teams from around the world, including participants from France, Italy, Japan, China, Slovakia, Switzerland, Germany, and the United States. It comprises three main phases.

The first phase is a verification phase, which involves a cross-comparison of high-frequency 3D simulations on simple topographies such as scarps, Gaussian hills/ridges, and triangular hills/ridges, for some of which analytical solutions are also available in the literature. The second phase is an initial validation phase focusing on more complex 3D simulations on a real topographic scarp in Cephalonia, Greece, where existing earthquake recordings are available. In this phase, the goal is to compare synthetic results with real-world measurements and simpler proxies. The final phase is a second validation phase targeting different topographic sites in Cephalonia, for which no prior earthquake measurements exist. New recordings will be collected during this phase, guided by insights from earlier simulations.

BENTO aims to assess the alignment of different numerical methods in evaluating topographic site effects, determine the meshing precision needed to capture small-scale topographic features at high frequencies, define reference rock sites on topographic reliefs, explore the relative influence of topographic parameters on amplification and de-amplification patterns, and address other critical aspects of the physics behind topographic site effects (e.g., focusing and defocusing of waves, wave diffraction).