The seismic records acquired during the 1994 M_W6.7 Northridge earthquake provide important data for studying the pulse-like ground motions in the vicinity of reverse faults. We selected 106 horizontal records from 468 strong ground motion records in the near-field region and rotated the original records into fault-parallel and fault-normal orientations. Large velocity pulses were simulated by the 3D finite difference method using a kinematic source model and a velocity structure model. Regression analysis was performed on the simulated and observed amplitudes of the velocity time history and response spectrum using the least-squares method. Our results show that the released energy and rupture time of asperities in the source model have important effects on the near-field velocity pulses, and the asperity near the initial rupture contributes more to the velocity pulses than does the asperity near the central region. The unidirectional and bidirectional characteristics of large velocity pulses are related to the thrust slip and rupture direction of the fault. The pulse period and the characteristic period are positively correlated with the rise time, and the pulse peak is regulated by multiple parameters of the subfaults. The distributions of the simulated PGV and Arias intensity agree well with the observed records, in which the contours exhibit asymmetric distribution and irregular elliptical attenuation in the near-field region, and the distributions exhibit a significant directivity along the fault. Moreover, the attenuation rate decreases with increasing distance from the fault. In addition, the fault-normal component is larger than that on the fault-parallel component, and the former decays faster. Velocity pulses larger than 30 cm/s are most likely to be distributed within approximately 15 km from the fault plane of the Northridge earthquake. Thus, the revealed pattern of the near-field velocity pulse-like ground motions indicates their close relation with the most severe earthquake effects.

中文翻译：

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北岭地震近场速度脉冲状地震动的数值模拟

1994 M _W期间获得的地震记录6.7北岭地震为研究逆断层附近的脉冲状地震动提供了重要数据。我们从近场区域的468个强地面运动记录中选择了106个水平记录，并将原始记录旋转到断层平行和断层法线方向。使用运动学源模型和速度结构模型，通过3D有限差分法模拟了大速度脉冲。使用最小二乘法对速度时程和响应谱的模拟和观察到的振幅进行回归分析。我们的结果表明，源模型中的粗糙物的释放能量和破裂时间对近场速度脉冲具有重要影响，初始破裂附近的粗糙比中心区域附近的粗糙对速度脉冲的贡献更大。大速度脉冲的单向和双向特性与断层的推力滑动和破裂方向有关。脉冲周期和特征周期与上升时间正相关，并且脉冲峰值由子故障的多个参数调节。模拟的PGV和Arias强度的分布与观察到的记录非常吻合，其中等高线在近场区域表现出不对称分布和椭圆形衰减不规则，并且沿着断层表现出明显的方向性。而且，衰减率随着距故障距离的增加而减小。此外，正常断层分量比平行断层分量大，前者衰减更快。大于30 cm / s的速度脉冲最有可能分布在距Northridge地震断层平面约15 km的范围内。因此，近场速度脉冲状地面运动的揭示模式表明它们与最严重的地震影响有着密切的关系。