Numerical simulation of near-fault ground strains and rotations from actual earthquakes with predominantly dip-slip mechanisms

IF 1.6 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS
Yenan Cao, George P. Mavroeidis
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Abstract

In the absence of records of near-fault ground strains and rotations from strong earthquakes, deterministic physics-based simulations have become an important tool for characterizing these motions in the low-frequency range (e.g., < 1.0 Hz). Building on a previous study of near-fault ground strains and rotations from actual strike-slip ruptures conducted by the authors, this article investigates the spatial and temporal characteristics of such motions generated by actual earthquakes with predominantly dip-slip mechanisms. This is achieved by performing forward ground-motion simulations of the 1994 Mw 6.7 Northridge, the 1989 Mw 6.9 Loma Prieta, and the 1985 Mw 8.1 Michoacan earthquakes using previously published finite-fault rupture models. For each considered seismic event, time histories of ground strains and rotations are generated at near-fault recording stations and at a dense grid of observation points. This is accomplished by finite differencing translational motions simulated at very closely spaced stations using a kinematic modeling approach. The simulation results show large-amplitude axial strain, shear strain, and rocking in the near-fault region. For the considered earthquakes, the maximum peak ground strain over all grid points is of the order of ~ 100–250 μstrain, whereas the maximum peak ground rocking ranges from ~ 100 to ~ 200 μrad. The attenuation characteristics of peak ground strains and rotations differ for the considered seismic events and depend on the component of interest and the rupture distance. Finally, peak ground rocking can be reasonably estimated from peak vertical ground velocity using a properly selected scaling factor despite the significant variability of the latter in the near-fault region. Filtering out the very low frequencies of ground motion (< 0.1 Hz), including the static offset, significantly affects the scaling factor.

Abstract Image

Abstract Image

以数值模拟以倾滑机制为主的实际地震产生的近断层地层应变和旋转
由于缺乏强地震近断层地面应变和旋转的记录,基于确定性物理学的模拟已成为描述低频范围(如 1.0 Hz)内这些运动特征的重要工具。本文以作者之前对实际击滑断裂产生的近断层地应变和旋转进行的研究为基础,研究了以倾滑机制为主的实际地震产生的此类运动的空间和时间特征。为此,作者使用之前发布的有限断层破裂模型对 1994 年 Mw 6.7 北岭地震、1989 年 Mw 6.9 洛马普列塔地震和 1985 年 Mw 8.1 米却肯地震进行了前向地动模拟。对于每个考虑的地震事件,都会在近断层记录站和密集的观测点网格上生成地面应变和旋转的时间历程。这是通过有限差分平移运动来实现的,平移运动是利用运动学建模方法在间距很近的台站进行模拟的。模拟结果显示了近断层区域的大振幅轴向应变、剪切应变和摇晃。对于所考虑的地震,所有网格点的最大地应变峰值约为 100-250 μstrain ,而最大地摇动峰值则在约 100 至约 200 μrad 之间。对于所考虑的地震事件,峰值地应变和地震动的衰减特性各不相同,并取决于相关成分和破裂距离。最后,尽管地震动峰值在近断层区有很大的变异性,但可以利用适当选择的缩放因子,从垂直地动速度峰值中合理地估算出地震动峰值。过滤掉极低频率的地面运动(0.1 赫兹),包括静态偏移,会对比例因子产生重大影响。
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来源期刊
Journal of Seismology
Journal of Seismology 地学-地球化学与地球物理
CiteScore
3.30
自引率
6.20%
发文量
67
审稿时长
3 months
期刊介绍: Journal of Seismology is an international journal specialising in all observational and theoretical aspects related to earthquake occurrence. Research topics may cover: seismotectonics, seismicity, historical seismicity, seismic source physics, strong ground motion studies, seismic hazard or risk, engineering seismology, physics of fault systems, triggered and induced seismicity, mining seismology, volcano seismology, earthquake prediction, structural investigations ranging from local to regional and global studies with a particular focus on passive experiments.
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