The horizontal-to-vertical spectral ratio (HVSR) method based on ambient noise recordings is a popular and efficient approach to estimate the seismic site effect parameters. This method is sufficiently robust in determining the predominant frequency (f₀) of the site, whereas its estimate of the amplification factor lacks consistency because generation mechanisms, source locations and proportions of the wave types making up ambient noise vary locally and are not well understood, in addition to lack of clarity in the theory of the HVSR method. As the generation mechanisms, source locations and wave compositions of the single- and double-frequency (SF and DF respectively) microseisms (0.05–0.5 Hz) are better studied compared to the noise in other frequency bands, this study focuses on investigating the site effects on the fundamental Rayleigh (Rg) waves in the SF and DF microseisms recorded at 30 Transportable Array stations in the east coast of the United States. HVSRs are calculated first to obtain f₀s as well as the unconsolidated sediment thicknesses (USTs). Then the polarization analyses are carried out to select the ellipsoids approximating the particle motions of the Rg waves and to estimate the HVSR of these Rg ellipsoids (HVSR_R). The polarization parameters and HVSR_R indicate that the Rg waves' particle motions form oblate ellipsoids in the UST range whose f₀ values fall within the DF band. Comparison of the observed HVSR and HVSR_R and the computed HVSR values based on the body wave and the Rayleigh wave theories shows that the observed HVSR in the DF band on bedrock and/or thin unconsolidated sediments are mainly due to the ellipticity of Rg waves, while those on thick unconsolidated sediments whose f₀ values fall within the DF band result from the combined effects of the ellipticity of Rg waves and multiple reflection of S-waves. This outcome will help develop procedures to improve the consistency of HVSR's amplification estimates and hence its reliability in seismic site effects analysis.

基于环境噪声记录的水平垂直谱比 (HVSR) 方法是一种流行且有效的估计地震现场效应参数的方法。该方法在确定主要频率 ( f ₀)，而其对放大系数的估计缺乏一致性，因为产生机制、源位置和构成环境噪声的波类型的比例在局部不同并且未被很好地理解，此外还缺乏 HVSR 理论的清晰度方法。由于与其他频段的噪声相比，对单频和双频（分别为 SF 和 DF）微震（0.05-0.5 Hz）的产生机制、震源位置和波组成进行了更好的研究，因此本研究重点研究了现场对美国东海岸 30 个可移动阵列台站记录的 SF 和 DF 微震中基本瑞利 ( R g) 波的影响。首先计算 HVSR 以获得f ₀s 以及松散沉积物厚度 (UST)。然后进行极化分析以选择近似于R g 波的粒子运动的椭球并估计这些R g 椭球的HVSR ( HVSR _R )。极化参数和HVSR _R表明R g 波的粒子运动在UST 范围内形成扁椭球，其f ₀值落在DF 带内。观察到的 HVSR 和HVSR _{R 的比较}基于体波和瑞利波理论计算的 HVSR 值表明，在基岩和/或薄的松散沉积物的 DF 波段观测到的 HVSR 主要是由于R g 波的椭圆度，而在厚松散的沉积物上观测到的 HVSR 主要是由于R g 波的椭圆度。由于R g 波的椭圆度和 S 波的多次反射的综合影响，f ₀值落在 DF 波段内。这一结果将有助于开发程序以提高 HVSR 放大估计的一致性，从而提高其在地震现场效应分析中的可靠性。