Empirical Green's function analysis: Taking the next step
Empirical Green's function analysis: Taking the next step
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DOI：
10.1029/96jb03488
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发表时间：
1997-03
影响因子：
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通讯作者：
S. Hough
中科院分区：
文献类型：
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作者：
S. Hough
提出了一种扩展的经验格林函数(EGF)方法，它包括使用标准的EGF反褶积来确定震源参数，然后对一组共同定位的事件的公共衰减参数进行反演。因此，可以使用三个或更多个并置事件的记录来约束单个路径衰减估计。我将这种方法应用于1995-1996年加利福尼亚州里奇克雷斯特地震序列的记录；我分析了四个震群，包括总共13个地震，震级在2.6到4.9之间。我首先得到拐角频率，它被用来推断布伦应力降估计。我得到了0.3-53 Mpa的应力降值(除1个外，其余都在0.3-11 Mpa之间)，没有解决应力降随弯矩增加的问题。在拐角频率受限的情况下，推断的衰减参数非常一致；它们意味着印度威尔斯河谷内的冲积沉积物的平均横波品质因数约为20-25。虽然得到的光谱拟合(使用拐角频率和κ)很好，但所分析的簇之间的残差是一致的。它们的频谱形状类似于山谷中层状低速结构的理论一维响应(由于绝对响应和震源频谱幅度之间的模糊性，无法用这种方法确定绝对场地响应)。我的研究表明，即使是这种微妙的场地响应，如果在仅针对震源和路径效应的反演中被忽略，也会显著偏离拐角频率和κ的估计。本文提出的多重EGF方法类似于震源、路径和场地效应的联合反演；同时定位地震集的使用似乎在提高所有三种估计的分辨率方面提供了显著的优势，特别是当数据来自于一个或多个具有相似场地响应的场地时。
An extension of the empirical Green's function (EGF) method is presented that involves determination of source parameters using standard EGF deconvolution, followed by inversion for a common attenuation parameter for a set of colocated events. Recordings of three or more colocated events can thus be used to constrain a single path attenuation estimate. I apply this method to recordings from the 1995–1996 Ridgecrest, California, earthquake sequence; I analyze four clusters consisting of 13 total events with magnitudes between 2.6 and 4.9. I first obtain corner frequencies, which are used to infer Brune stress drop estimates. I obtain stress drop values of 0.3–53 MPa (with all but one between 0.3 and 11 MPa), with no resolved increase of stress drop with moment. With the corner frequencies constrained, the inferred attenuation parameters are very consistent; they imply an average shear wave quality factor of approximately 20–25 for alluvial sediments within the Indian Wells Valley. Although the resultant spectral fitting (using corner frequency and κ) is good, the residuals are consistent among the clusters analyzed. Their spectral shape is similar to the the theoretical one-dimensional response of a layered low-velocity structure in the valley (an absolute site response cannot be determined by this method, because of an ambiguity between absolute response and source spectral amplitudes). I show that even this subtle site response can significantly bias estimates of corner frequency and κ, if it is ignored in an inversion for only source and path effects. The multiple-EGF method presented in this paper is analogous to a joint inversion for source, path, and site effects; the use of colocated sets of earthquakes appears to offer significant advantages in improving resolution of all three estimates, especially if data are from a single site or sites with similar site response.