Verification of Subsurface S-Wave Velocity Structure Model in Iwaki City, Fukushima Prefecture, Using a Dense Seismic Array

Abstract eng:
A dense seismic/microtremor array consisting of 16 sensors was deployed in Iwaki city, Fukushima prefecture, Japan from November 2014 to September 2015. During the observation period, seismic signals from at least 100 felt earthquakes (3.5 ≤ Mw ≤ 7.9) as well as continuous microtremors were recorded. In this study we used the event data to investigate site amplification factors beneath the observation sites and also used microtremor data to estimate propagation properties of surface wave in the entire area, for the verification of an existing three-dimensional seismic velocity structure model. The site amplification factors estimated from spectral inversion method indicate the spatial variations of subsurface soil structure and the Rayleigh-wave dispersion properties derived from the seismic interferometry technique show lower group velocities compared with the theoretical curve from the existing model. On the other hand, predicted dominant frequency and group velocity of Rayleigh wave based on one-dimensional S-wave structure model from large-scale microtremor array survey show similar trends with the estimations. The results show that the combined use of the dense microtremor and strong motion data in a local area of high seismicity can be a powerful tool for the improvement of subsurface structure model.

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