摘要
地震危险性评估对于确定工程抗震设防等级、制定城市规划、减轻地震灾害及地震引发的滑坡、泥石流等其他灾害具有重要意义.在地震波场传播过程中,能够造成波场能量衰减的因素包括多角度散射、频散及球面扩散.针对震后的地震动场空间分布特征开展数值模拟时,是否考虑这3项因素对于实际计算结果有着直接影响.文中以地震波场在滞弹性介质中的物理频散特征为讨论对象,通过模拟计算情景地震在简单一维模型中引起的波场频散及地震动时程分布,讨论频散对地震动场空间分布及地震危险性分析的影响.然后,以2021年漾濞MS6.4地震为例,进一步分析滞弹性介质的物理频散对地震危险性分析的意义.在经典地震动参数预测方程(GMPE)的基础上,基于物理的地震动模拟对于进一步获得更加可靠的地震动水平及地震危险性的物理评估都具有重要意义.
Abstract
Seismic hazard assessment is crucial for determining engineering fortification levels,guiding urban planning,mitigating earthquake disasters,and addressing secondary hazards such as landslides and mudslides triggered by earthquakes.Energy attenuation during seismic wave propagation is influenced by multi-angle scattering,physical dispersion,and geometric spreading.When conducting numerical simulations of post-earthquake ground motion,accounting for these factors significantly affects the accuracy of hazard assessments.This paper examines the physical dispersion characteristics of seismic waves in viscoelastic media.Through simulations of velocity dispersion and seismic wave time distribution in a simple one-dimensional model,we explore the impact of dispersion on the spatial distribution of seismic motion and its implications for seismic hazard assessment.A case study of the 2021 Yangbi MS6.4 earthquake further illustrates the importance of considering physical dispersion in seismic hazard analysis.In contrast to traditional ground motion prediction equations(GMPE),physics-based simulations of ground motion provide more reliable estimates of seismic hazard levels and enhance the accuracy of hazard assessments.It is well-established that,excluding site effects,peak ground motion parameters on bedrock decrease with increasing epicentral distance.However,considering the wave field dispersion characteristics reveals that peak ground motion parameters do not always decrease monotonically with distance;in some cases,they may even slightly increase.This highlights the complexity of seismic wave propagation through viscoelastic media.Further validation of these findings through refined,scenario-based numerical simulations is necessary.Additionally,with increasing epicentral distance,the amplitude of ground motion time histories decreases,while their duration increases.This low-frequency,long-duration seismic motion may be amplified under specific site conditions,such as in basins.The influence of the non-uniform viscoelastic medium results in varying attenuation rates for horizontal peak ground motion parameters at different angles.The findings of this study have important implications for national security,critical infrastructure,unconventional energy development,and secondary hazards such as landslides and mudslides.The integration of source physics,seismic wave theory,medium structure imaging,and structural stress analysis is essential for improving the accuracy and reliability of seismic hazard assessments.
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