Estimation of shallow S-wave velocity structure using microtremor array exploration at temporary strong motion observation stations for aftershocks of the 2016 Kumamoto earthquake
Tóm tắt
Shallow S-wave velocity V
S profiles were estimated for 26 temporary strong motion observation sites surrounding the epicenters of a sequence of the 2016 Kumamoto earthquake. The microtremor array method was used to gather the dispersion characteristics of Rayleigh waves. V
S profiles were obtained by inverting the dispersion curves for each site and those of three permanent strong motion stations that recorded the sequence of seismic events. The shallow V
S profiles near two of the permanent strong motion stations in the town of Mashiki were almost identical. However, the V
S profiles at other stations varied. The V
S profiles were found to have the common feature of the uppermost low-velocity layer being widely distributed from Mashiki to the village of Minami-Aso, and it was especially thick in the areas that suffered heavy damage. This low-velocity layer was a major contributor to the site amplification. The horizontal-to-vertical spectral ratios of the microtremors indicate that both the shallow soil and deep sedimentary layers may control the site response characteristics over a broad frequency range.
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