Seismic Wave Amplification in 3D Alluvial Basins: 3D/1D Amplification Ratios from Fast Multipole BEM Simulations

TL;DR

This study uses advanced numerical simulations to analyze how seismic wave amplification in 3D alluvial basins differs from 1D models, providing practical rules for predicting amplification based on key physical parameters.

Contribution

It introduces a novel approach using Fast Multipole Boundary Element Method to quantify 3D/1D amplification ratios considering basin asymmetry and physical parameters.

Findings

Impedance contrast and shape ratio are key for amplification.

Derived simple rules for fundamental frequency and amplification factors.

3D basin asymmetry affects amplification and is incorporated into predictive rules.

Abstract

In this work, we study seismic wave amplification in alluvial basins having 3D standard geometries through the Fast Multipole Boundary Element Method in the frequency domain. We investigate how much 3D amplification differs from the 1D (horizontal layering) case. Considering incident fields of plane harmonic waves, we examine the relationships between the amplification level and the most relevant physical parameters of the problem (impedance contrast, 3D aspect ratio, vertical and oblique incidence of plane waves). The FMBEM results show that the most important parameters for wave amplification are the impedance contrast and the so-called equivalent shape ratio. Using these two parameters, we derive simple rules to compute the fundamental frequency for various 3D basin shapes and the corresponding 3D/1D amplification factor for 5% damping. Effects on amplification due to 3D basin asymmetry are also studied and incorporated in the derived rules.