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The Effect of Velocity Inversions on H/V

机译:速度反转对H / V的影响

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We analyzed the phenomenology of microtremor H/V curves under inversions in the shear-wave velocity (V-s) profile in the subsoil. Under no V-s inversion the spectral signature of the H/V peaks is found to be 'eye-shaped' with the horizontal components higher than the vertical. Conversely, under negative velocity gradients, numerous of differences emerge. I) A H/V ratio below 1 is observed for a wide range of frequencies, due to the decrease of the horizontal components below the vertical one. II) In the presence of persistent H/V < 1, small bumps in the H/V ratio given by local minima in the vertical spectral component may represent the relics of the peaks indicating resonances and stratigraphic discontinuities. As a consequence, in the presence of velocity inversions the H/V > 2 SESAME (2004) criterion fails but a stratigraphic interpretation may still be possible. III) The H/V curves should always be interpreted together with the single component spectra. IV) Microtremor H/V measurements for stratigraphic/microzonation purposes on stiff artificial soils, (asphalt, concrete, cement, pavements) should always be avoided since the latter often produce velocity inversions. This may have consequences in the intermediate to high frequency domain ( > 1 Hz) also in the application of reference site methods, like H-site/H-bedrock, to microtremor. Theoretical modeling confirms these experimental findings.
机译:我们分析了地下土壤剪切波速度(V-s)剖面反演下的微震H / V曲线的现象学。在没有V-s反转的情况下,发现H / V峰的频谱特征是“眼形”的,其水平分量高于垂直分量。相反,在负速度梯度下,会出现许多差异。 I)由于水平分量减少到垂直分量以下,因此在宽范围的频率下均观察到H / V比低于1。 II)在存在永久H / V <1的情况下,由垂直光谱分量中的局部极小值给出的H / V比中的小凸起可能表示峰的残留物,表明共振和地层间断。结果,在存在速度反演的情况下,H / V> 2 SESAME(2004)判据失败了,但地层解释仍然可能。 III)H / V曲线应始终与单组分光谱一起解释。 IV)应始终避免在坚硬的人造土壤(沥青,混凝土,水泥,路面)上进行地层/微区目的微震H / V测量,因为后者经常会产生速度倒转。在将参考部位方法(例如H部位/ H-基岩)应用于微震中时,这也可能在中高频范围(> 1 Hz)中产生影响。理论模型证实了这些实验结果。

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