The Horizontal-to-Vertical Spectral Ratio (HVSR) of ambient vibration measurements is a common tool to explore near surface shear wave velocity (Vs) structure. HVSR is often applied for earthquake risk assessments and civil engineering projects. Ambient vibration signal originates from the combination of a multitude of natural and man-made sources. Ambient vibration sources can be any ground motion inducing phenomena, e.g., ocean waves, wind, industrial activity or road traffic, where each source does not need to be strictly stationary even during short times. Typically, the Fast Fourier Transform (FFT) is applied to obtain spectral information from the measured time series in order to estimate the HVSR, even though possible non-stationarity may bias the spectra and HVSR estimates. This problem can be alleviated by employing the Hilbert–Huang Transform (HHT) instead of FFT. Comparing 1D inversion results for FFT and HHT-based HVSR estimates from data measured at a well studied, urban, permanent station, we find that HHT-based inversion models may yield a lower data misfit ${\chi }^2$ by up to a factor of 25, a more appropriate Vs model according to available well-log lithology, and higher confidence in the achieved model.

中文翻译：

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Hilbert–Huang变换获得的环境振动的垂直与垂直光谱比

环境振动测量的水平频谱比（HVSR）是探索近地表剪切波速度（Vs）结构的常用工具。HVSR通常用于地震风险评估和土木工程项目。环境振动信号源于多种自然和人工来源的组合。环境振动源可以是任何引起地面运动的现象，例如海浪，风，工业活动或道路交通，其中即使在很短的时间内，每个振动源也不必严格固定。通常，应用快速傅立叶变换（FFT）从测得的时间序列中获取光谱信息，以便估算HVSR，即使可能的非平稳性可能会使光谱和HVSR估算值产生偏差。通过使用希尔伯特-黄氏变换（HHT）而不是FFT可以缓解此问题。从在经过充分研究的城市永久性站点测得的数据比较FFT和基于HHT的HVSR估计的一维反演结果，我们发现基于HHT的反演模型可能会产生较低的数据失配${\chi }^{\mathrm{2个}}$ 根据可用的测井岩性，最合适的Vs模型最多可增加25倍，并且对所获得的模型有更高的信心。