Comparison of phase velocities from array measurements of Rayleigh waves associated with microtremor and results calculated from borehole shear-wave velocity profiles
Comparison of phase velocities from array measurements of Rayleigh waves associated with microtremor and results calculated from borehole shear-wave velocity profiles
复制标题
与微震相关的瑞利波阵列测量相速度与井眼剪切波速度剖面计算结果的比较
DOI：
10.3133/ofr00216
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发表时间：
2000
期刊：
影响因子：
--
通讯作者：
L. Brown
中科院分区：
文献类型：
--
作者：
Hsi;D. Boore;W. B. Joyner;D. Oppenheimer;R. E. Warrick;Wenbo Zhang;J. Hamilton;L. Brown
剪切波速度（VS）被广泛用于地震地面运动场地特征。现在，VS数据主要是利用钻孔方法获得的。然而，钻孔是昂贵的。非侵入式地面方法对于获得VS信息是不昂贵的，但与直接钻孔测量的比较并不多。由于每种地面方法的数据解释中使用了不同的假设，并且工程结构的场地特征化涉及公共安全，因此通过与钻孔测量进行额外比较来验证地面方法非常重要。我们将特定地面方法（与微动相关的表面波阵列测量）获得的结果与钻孔方法获得的结果进行比较。我们用100米孔径的10单元三角形嵌套阵测量了两个加州地点的表面波相速度，即靠近赫米特的加纳谷和霍利斯特市机场。加纳谷遗址位于一个古老的湖床，水饱和的沉积物覆盖在花岗岩基岩顶部的分解花岗岩上。我们的阵列被部署在一个位置，地震速度已被确定为500米的深度钻孔方法。在霍利斯特，近地表沉积物包括粘土，沙子和砾石，我们确定相速度使用一个阵列位于接近60米深的钻孔，井下速度测井已经存在。因为我们要评估的测量不复杂的反演过程中引入的不确定性，我们比较我们的相速度的结果与钻孔VS深度剖面计算基本模式瑞利波相速度从地球模型构建的钻孔数据。在加纳谷，当波长小于2倍阵列孔径时，由阵列测量得到的相速度与计算得到的瑞利波速度的一致性优于11%。当波长比阵列孔径大2倍时，测量误差变大.在霍利斯特，在3.9 Hz（靠近微动频带的上边缘）处测得的相速度在计算的瑞利波速度的20%以内。由于剪切波速度是控制瑞利波相速度的主要因素，比较表明，这种非侵入性的方法可以提供足够的地面运动估计VS信息。
Shear-wave velocities (VS) are widely used for earthquake ground- motion site characterization. VS data are now largely obtained using borehole meth- ods. Drilling holes, however, is expensive. Nonintrusive surface methods are inex- pensive for obtaining VS information, but not many comparisons with direct borehole measurements have been published. Because different assumptions are used in data interpretation of each surface method and public safety is involved in site character- ization for engineering structures, it is important to validate the surface methods by additional comparisons with borehole measurements. We compare results obtained from a particular surface method (array measurement of surface waves associated with microtremor) with results obtained from borehole methods. Using a 10-element nested-triangular array of 100-m aperture, we measured surface-wave phase veloci- ties at two California sites, Garner Valley near Hemet and Hollister Municipal Air- port. The Garner Valley site is located at an ancient lake bed where water-saturated sediment overlies decomposed granite on top of granite bedrock. Our array was deployed at a location where seismic velocities had been determined to a depth of 500 m by borehole methods. At Hollister, where the near-surface sediment consists of clay, sand, and gravel, we determined phase velocities using an array located close to a 60-m deep borehole where downhole velocity logs already exist. Because we want to assess the measurements uncomplicated by uncertainties introduced by the inversion process, we compare our phase-velocity results with the borehole VS depth profile by calculating fundamental-mode Rayleigh-wave phase velocities from an earth model constructed from the borehole data. For wavelengths less than 2 times of the array aperture at Garner Valley, phase-velocity results from array measure- ments agree with the calculated Rayleigh-wave velocities to better than 11%. Mea- surement errors become larger for wavelengths 2 times greater than the array aper- ture. At Hollister, the measured phase velocity at 3.9 Hz (near the upper edge of the microtremor frequency band) is within 20% of the calculated Rayleigh-wave veloc- ity. Because shear-wave velocity is the predominant factor controlling Rayleigh- wave phase velocities, the comparisons suggest that this nonintrusive method can provide VS information adequate for ground-motion estimation.