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| Simulation of broadband seismic wave propagation in a crustal half-space in frequency-wavenumber domain generated by shear dislocation sources |
| LIANG Jianwen1,2,WU Mengtao1,2,BA Zhenning1,2 |
| (1. State Key Laboratory of Hydraulic Engineering Simulation and Safety,Tianjin University,Tianjin 300350,China;2. Department of Civil Engineering,Tianjin University,Tianjin 300350,China) |
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Abstract Simulation of seismic wave propagation generated by shear dislocation sources is a theoretical basis for near-fault ground motion researches. However,existing deterministic methods have certain shortcomings in high-frequency solutions and cross-scale calculations. This paper proposes a frequency-wavenumber method for multi-scale modelling of broadband seismic wave propagation in the stratified half-space due to dislocations,which can effectively solve the broadband seismic response problem(covering 0.1–10 Hz engineering structure sensitive frequencies) from high-velocity crustal scale(kilometre level) to low-velocity geotechnical scale(metre level). The Fourier-Hankel transformation is used to convert the 3D wave equations from time-space domain to frequency-wave number domain in the cylindrical coordinate system,and the dynamic response of a viscoelastic layered half-space due to a dislocation source is derived by the modified stiffness matrix method in conjunction with the displacement-stress discontinuity conditions. The correctness and accuracy of the proposed method are first verified by comparing with the classical Haskell method,and then a cross-scale site model embedded in the Tianjin crustal structure is established to focus on the effects of the source frequency and the near-surface soft interlayer on earthquake ground motions. The results show that the new method is very suitable for modelling broadband ground motions and low-velocity subdivided layers,and the complex propagation processes such as reflection,conversion and transmission of seismic waves at layer interfaces as well as the ground motion characteristics due to dislocation sources can be clearly observed. The ground motions of soft sites are significantly affected by the source frequency,and the high frequency excitation can increase the intensity and extent of the earthquake radiation energy,which may lead to more serious surface rupture and structural damage. The near-surface soft interlayers with different buried depths and thicknesses have important impact on the seismic responses of soft sites,and the superposition of the filtering and amplifying effects from site and the isolation effect from soft interlayers makes the surface response very complicated.
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