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Fault Zone Imaging from Correlations of Aftershock Waveforms

机译：余震波形相关性的故障区域成像

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摘要

We image an active fault zone environment using cross correlations of 154 15 s long 1992 Landers earthquake aftershock seismograms recorded along a line array. A group velocity and phase velocity dispersion analysis of the reconstructed Rayleigh waves and Love waves yields shear wave velocity images of the top 100 m along the 800 m long array that consists of 22 three component stations. Estimates of the position, width, and seismic velocity of a low-velocity zone are in good agreement with the findings of previous fault zone trapped waves studies. Our preferred solution indicates the zone is offset from the surface break to the east, 100-200 m wide, and characterized by a 30% velocity reduction. Imaging in the 2-6 Hz range resolves further a high-velocity body of similar width to the west of the fault break. Symmetry and shape of zero-lag correlation fields or focal spots indicate a frequency and position dependent wavefield composition. At frequencies greater than 4 Hz surface wave propagation dominates, whereas at lower frequencies the correlation field also exhibits signatures of body waves that likely interact with the high-velocity zone. The polarization and late arrival times of coherent wavefronts observed above the low-velocity zone indicate reflections associated with velocity contrasts in the fault zone environment. Our study highlights the utility of the high-frequency correlation wavefield obtained from records of local and regional seismicity. The approach does not depend on knowledge of earthquake source parameters, which suggests the method can return images quickly during aftershock campaigns to guide network updates for optimal coverage of interesting geological features.
机译：我们使用154 15 S长的1992年载机地震余震沿线阵列记录的地震余震地震图的互相关性。重建的瑞利波和爱波的群体速度和相位速度分散分析沿着800米长的阵列产生前100米的剪切波速度图像，该阵列由22个三个组件站组成。低速区的位置，宽度和地震速度的估计与先前故障区域被困波的研究结果吻合良好。我们的首选解决方案表示该区域偏离从表面突破到东部，100-200米宽，其特征在于30％的速度降低。在2-6 Hz范围内的成像将进一步解决了故障断裂西部类似宽度的高速体。零滞后相关场或焦斑的对称性和形状表示频率和位置相关的波场组合。在大于4Hz的频率大于4Hz的表面波传播中，而在较低频率下，相关领域还表现出可能与高速区相互作用的身体波的签名。在低速区上方观察到的相干波前的偏振和后退时间表示与故障区域环境中的速度对比相关的反射。我们的研究突出了从局部和区域地震记录获得的高频相关波场的效用。该方法不依赖于地震源参数的知识，这表明该方法可以在余震期间快速返回图像，以指导网络更新以获得有趣的地质特征的最佳覆盖范围。

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