SUMMARY Previous studies have demonstrated that finite-fault simulations of actual or hypothetical earthquakes using deterministic, physics-based simulation techniques constitute an effective tool for characterizing near-fault ground strains and rotations in the low-frequency range. The characteristics of these motions are further investigated in this study by performing forward ground-motion simulations of three well-documented strike-slip earthquakes (i.e. 2004 Mw 6.0 Parkfield, 1979 Mw 6.5 Imperial Valley and 1999 Mw 7.5 Izmit) using models of the seismic source and crustal structure available in the literature. Time histories of ground strains and rotations are numerically generated at near-fault stations and at a dense grid of observation points extending over the causative fault. This is achieved by finite differencing translational motions simulated at very closely spaced stations using a kinematic modelling approach. The simulation results show that the three strike-slip earthquakes produce large-amplitude pulse-like shear strain and torsion in the forward direction of rupture propagation. The time histories of specific components of displacement gradient, strain and rotation at near-fault stations can be estimated from those of ground velocities using a phase velocity, whereas peak ground torsions in the near-fault region can be reasonably estimated from peak horizontal ground velocities using a scaling factor. However, both the phase velocity and the scaling factor exhibit significant variability in the near-fault region of the considered earthquakes. The concept of isochrones is also utilized to associate fault rupture characteristics with near-fault ground strains and rotations. The results indicate that the seismic energy radiated from the high-isochrone-velocity region of the fault—which encompasses areas of large slip locally driven by high stress drop—arrives at a near-fault station in a short time interval that coincides with the time window of the large-amplitude pulse-like shear strain and torsion.

中文翻译：

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模拟来自实际走滑地震的近断层地面应变和旋转：2004 Mw 6.0 Parkfield、1979 Mw 6.5 Imperial Valley 和 1999 Mw 7.5 Izmit 地震的案例研究

总结 先前的研究表明，使用确定性的、基于物理的模拟技术对实际或假设地震进行有限断层模拟是表征低频范围内近断层地面应变和旋转的有效工具。本研究通过使用地震模型对三个有充分记录的走滑地震（即 2004 Mw 6.0 Parkfield、1979 Mw 6.5 Imperial Valley 和 1999 Mw 7.5 Izmit）进行正向地面运动模拟，进一步研究了这些运动的特征。来源和地壳结构在文献中可用。地面应变和旋转的时间历史是在断层附近的站点和在成因断层上延伸的密集观测点网格处以数值方式生成的。这是通过使用运动学建模方法在非常接近的站点上模拟的有限差分平移运动来实现的。模拟结果表明，3次走滑地震在破裂传播的正向产生大振幅脉冲状剪切应变和扭转。近断层台站位移梯度、应变和旋转的特定分量的时程可以使用相速度从地速估计，而近断层区域的峰值地扭可以从峰值水平地速合理估计使用比例因子。然而，在所考虑地震的近断层区域，相速度和比例因子都表现出显着的可变性。等时线的概念也用于将断层破裂特征与近断层地面应变和旋转联系起来。结果表明，从断层的高等时速度区域（包括由高应力降驱动的局部大滑动区域）辐射的地震能量在与时间一致的短时间间隔内到达近断层台站。大振幅脉冲样剪切应变和扭转的窗口。