A multidimension source model for generating broadband ground motions with deterministic 3D numerical simulations is proposed in this article. In this model, the source is composed of several superimposed layers, and the total seismic moment is assigned to these layers in different proportions. Each layer exactly fills up the seismic fault and is uniformly divided into subsources with size decreased progressively to reflect different levels of rupture details. Hence, the proposed multidimension source model may consider the realistic rupture process of an earthquake, that is, the spatial and temporal heterogeneity of source parameters, and generate broadband ground motions. To verify this source model, the 1994 Northridge earthquake is simulated with four multidimension source models, based on different source inversion results. The amplitudes, durations, and spectral characteristics of the observed ground motions of the 1994 Northridge earthquake are respectably reproduced in a range of frequencies up to 5 Hz. In addition, a scenario earthquake is also simulated with four multidimension source models, with different synthetic rupture process. The simulated ground motions of the scenario earthquake are generally in good agreement with the Next Generation Attenuation-West 2 ground-motion prediction equations. This demonstrates that it is promising to simulate realistic broadband ground motions of strong earthquakes with a proper source description and realistic Earth models.
Generating broadband ground motions requires fine enough scales in the source model, but small scales may lead to unacceptable computational efforts for source inversion. To resolve this challenge, a novel kinematic source inversion method is proposed in this study to map the detailed rupture process associated with broadband seismic radiation. This method addresses two key issues for imaging the rupture process of earthquakes: proper source models describing the rupture process and accurate Green’s functions. For the first issue, the rupture process of target earthquakes is modeled by a recently proposed multidimension source model, which is composed of several superimposed layers with degressive scales to generate broadband ground motions. Due to the self‐similarity of the parameters of subsource on different layers, the number of variables to be considered in the inversion procedure is comparable to that of the conventional finite‐fault source model. For the second issue, the spectral element method is used to compute the Green’s functions with high‐resolution topography and three‐dimensional (3D) velocity structures. The introduction of accurate 3D velocity structures enables to reproduce the ground motions of target earthquakes in a wide range of frequency. With the multidimension source model and accurate Green’s functions, an evolutionary many‐objective optimization algorithm is used to search for the best rupture‐process parameters. The rupture process of the 1992 Landers earthquake is mapped by the proposed inversion method, and the ground motions from the forward simulation with the inverted rupture process have an impressive agreement with the records in a wide range of frequency.
The determination of spatially‐varying broadband ground motions is a prerequisite for the seismic analysis of dams. However, generating realistic ground motions at a specific dam site remains a challenge. Source‐to‐structure simulation, which considers source, propagation path, and site, is a promising way to reasonably synthesize site‐specific ground motions. This paper proposes a practical framework for the seismic analysis of dams based on a deterministic numerical source‐to‐structure simulation. The site‐specific broadband ground motions are generated by a physics‐based 3D numerical simulation using the spectral element method (SEM) in a coarse mesh, while the nonlinear dynamic response of the dam is simulated by the finite element method (FEM) in a fine mesh. The proposed framework bridges the gap between wavefield simulation and seismic analysis of dams. The seismic response analysis of Pacoima dam during the 1994 Northridge earthquake was conducted as a case study, making it the first demonstration of a complete source‐to‐structure simulation for realistic concrete dams using the purely numerical method. Results show that the calculated seismic response agrees with the observation, thus indicating the utility of the proposed framework for source‐to‐dam simulation.
The response spectrum is generally adopted in the seismic design to represent the seismic fortification level, but the structural dynamic analysis requires the ground motions as an input. However, ground motions generated by the traditional spectral matching methods do not have site‐related physical backgrounds for the target site. In this study, a physics‐based spectral matching (PBSM) method is developed to generate fully site‐related broadband ground motions (i.e., the generated ground motions have real physical backgrounds for the target site, including the source process, propagation path, and local site conditions) that are compatible to the target spectrum. In this method, the three‐dimensional (3D) numerical model around the target site is constructed to calculate the strain Green's tensors of all potential source locations using adjoint simulations. The variable space dimension of the seismic source is significantly reduced by applying the self‐similar feature of the multidimension source model, so that the optimization algorithm can be used to search for the rupture process that generates the physics‐based and spectrum‐matched ground motions (abbreviated to PBSM ground motions). The proposed method is applied to the Xiluodu dam in China. Compared with the traditional techniques, the generated ground motions have fully site‐related physical backgrounds and are compatible to the target spectrum. Additionally, as this method generates broadband ground motions based on the deterministic rupture process, any features of ground motions, such as large velocity pulses, can be taken into account throughout the optimization process. This study introduces the deterministic physical backgrounds of earthquakes to performance‐based seismic design and analysis. The proposed method may have a significant application potential in earthquake engineering.
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