Comparing EGF Methods for Estimating Corner Frequency and Stress Drop From P Wave Spectra
Comparing EGF Methods for Estimating Corner Frequency and Stress Drop From P Wave Spectra
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比较根据 P 波谱估计角频率和应力降的 EGF 方法
DOI：
10.1029/2018jb016957
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Wei Wang
中科院分区：
文献类型：
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作者：
P. Shearer;R. Abercrombie;D. Trugman;Wei Wang
经验绿色函数（EGFs）被广泛应用于校正地震谱的衰减和其他路径效应，以估计拐角频率和应力降，但这些源参数估计往往表现出不同的研究之间的一致性差。我们通过分析1992年兰德斯地震的3,000多个余震来研究这个问题。我们应用并比较了两种不同的分析和建模方法：（1）光谱分解和全局EGF拟合方法和（2）更传统的EGF光谱比建模方法。我们发现，频谱分解产生的事件条款是一致的堆栈的频谱比为个别事件，但源参数估计方法之间的差异。差异的主要来源来自用于估计EGF的建模方法。全局EGF拟合方法受到绝对应力降、应力降随力矩缩放和高频衰减率之间的参数权衡的影响，但其优点是即使它们的绝对水平没有得到很好的解析，集群中不同事件之间的相对谱形状和应力降也得到很好的解析。频谱比方法求解每个目标事件的不同EGF，而不对较小事件的拐角频率fc施加任何约束，因此可以产生目标事件fc的有偏结果。对小事件fc施加约束可以提高谱比方法的性能，并使两种方法产生非常相似的结果。
Empirical Green's functions (EGFs) are widely applied to correct earthquake spectra for attenuation and other path effects in order to estimate corner frequencies and stress drops, but these source parameter estimates often exhibit poor agreement between different studies. We examine this issue by analyzing a compact cluster of over 3,000 aftershocks of the 1992 Landers earthquake. We apply and compare two different analysis and modeling methods: (1) the spectral decomposition and global EGF fitting approach and (2) a more traditional EGF method of modeling spectral ratios. We find that spectral decomposition yields event terms that are consistent with stacks of spectral ratios for individual events, but source parameter estimates nonetheless vary between the methods. The main source of differences comes from the modeling approach used to estimate the EGF. The global EGF‐fitting approach suffers from parameter trade‐offs among the absolute stress drop, the stress drop scaling with moment, and the high‐frequency falloff rate but has the advantage that the relative spectral shapes and stress drops among the different events in the cluster are well resolved even if their absolute levels are not. The spectral ratio approach solves for a different EGF for each target event without imposing any constraint on the corner frequency, fc, of the smaller events, and so can produce biased results for target event fc. Placing constraints on the small‐event fc improves the performance of the spectral ratio method and enables the two methods to yield very similar results.