In this study, the inversion modeling method variability of S-wave velocity structure results by inverting/forward-modeling waveforms and HVSR curves is investigated. For this purpose, eight KiK-net seismic stations using 636 foreshocks, mainshock of the 2011 Tohoku earthquake, and 4983 aftershocks obtained from KiK-net are used. The most reliable and representative inverted S-wave velocity structures are based on close fitting of the theoretical to the observed data of waveforms and HVSR curves. The inverted S-wave velocity structures derived from the total stress analyses are showing high degrees of similarity and consistency using both EW and NS components and evidenced by the isotropic HVSRs directionality related to the linear and nonlinear site effects. Conversely, stiffness variations due to nonlinearity, inferred from inverted S-wave velocity structures derived from the diffuse field assumption, significantly correspond with stiffness variations evaluated from the observed fundamental resonance frequencies. The corresponding percent of reduction and recovery reflect low variability in S-wave velocities that result from inversion modeling based on diffuse field assumption. Qualitatively, the presence of the stiffness degradation process due to linear and nonlinear site responses could be obviously detected using both inversion modeling methods based on total stress analyses and diffuse field assumption. Quantitatively, the precision of the nonlinearity evaluation is questionable due to significant uncertainties in the inverted S-wave velocity structures inferred from both inversion modeling methods. These uncertainties are strongly dependent on the theory of each inversion modeling method. The use of complementary methods with more prior information is suggested to resolve the nonuniqueness of the inverted S-wave velocities and hence overconfidence in the precision of the nonlinearity evaluation.

在这项研究中，研究了通过反转/正向建模波形和HVSR曲线得到的S波速度结构的反演方法的可变性。为此，使用了使用636个前震，2011年东北地震的主震和从KiK-net获得的4983次余震的八个KiK-net地震台站。最可靠和最具代表性的倒S波速度结构是基于理论上与波形和HVSR曲线的观测数据的紧密拟合。倒S从总应力分析得出的波速结构使用EW和NS分量显示出高度的相似性和一致性，并由与线性和非线性站点效应相关的各向同性HVSR方向性证明。相反地​​，由非线性所引起的刚度变化，从由扩散场假设推导的倒S波速度结构推断出，与根据观测到的基本共振频率评估的刚度变化显着对应。减少和恢复的相应百分比反映了S的低变异性波速度是由基于扩散场假设的反演模型得出的。定性地，使用基于总应力分析和扩散场假设的反演建模方法，可以明显地检测到由于线性和非线性部位响应而导致的刚度降低过程。在定量上，由于从两种反演模型方法推断出的反S波速度结构存在明显的不确定性，非线性评估的准确性值得怀疑。这些不确定性在很大程度上取决于每种反演建模方法的理论。建议使用具有更多先验信息的互补方法来解决倒S的不唯一性速度，因此对非线性评估的准确性过于自信。