The relationship between Vs, Vp and depth based on PS-logging data at K-NET and KiK-net sites

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  • K-NET・KiK-netのPS検層記録に基づくVs・Vpおよび深さの関係
  • K-NET ・ KiK-net ノ PSケンソウ キロク ニ モトズク Vs ・ Vp オヨビ フカサ ノ カンケイ

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Abstract

<p>P-wave velocity (Vp) is an important parameter to construct a seismic model of the subsurface by using microtremors and earthquake ground motions, though Vp is not so strongly constrained as S-wave velocity (Vs). In order to reflect the ground survey information in Japan to the Vp structure, we investigated the relationship between Vs, Vp, and depth by using PS-logging data at the all sites of K-NET and KiK-net. Vp values are concentrated at around 500 m/s and 1500 m/s when Vs is lower than 1000 m/s, where these concentrated areas show the characteristics of the unsaturated soil and the saturated soil, respectively. The most of the Vp values in the layer shallower than 4 m are about 500 m/s, which suggests the dominance of the unsaturated soil, while the most of Vp values in the layer deeper than 4 m are larger than about 1500 m/s, which suggests the dominance of the saturated soil there. We also investigated those relationships for different types of the soil at K-NET sites. Although each soil type has their own depth range, the all soil types show similar relationships between Vs, Vp, and depth. Then considering the depth profile of Vp, we divided the dataset into two by the depth, which is shallower or deeper than 4 m, and calculated the geometric mean of Vp and the geometric standard deviation in every Vs bins of 200 m/s. Finally we obtained the regression curves for the average and standard deviation of Vp estimated from Vs to get the Vp conversion functions from Vs, which can be applied to the wide Vs range. We also obtained the regression curves for two datasets with Vp lower and higher than 1200 m/s. These regression curves can be applied in case that the groundwater level is known.</p>

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