Near-Surface Geophysical Profiling Near Former Location of K-NET Tsukidate Strong Motion Station in Miyagi Prefecture, Japan

抄録

During the 2011 Earthquake off the Pacific Coast of Tohoku, high acceleration records with a PGA of 2.7 G were reported at the K-NET Tsukidate station (MYG004), where a maximum seismic intensity of 7 on the Japan Meteorological Agency (JMA) scale was observed. However, no major damage to the wooden houses in the area surrounding the station was reported. The objectives of this study are to obtain a 2D shallow soil profile of the area around the Tsukidate strong motion station (MYG004) located on the top of a 5 m cliff, and also to provide basic material for a detailed understanding of the high accelerations during the earthquake. We conducted a seismic refraction survey west of the station, and we used a full-waveform inversion of the acquired seismic data to retrieve a 2D shallow soil profile. The inverted 2D soil model underlines a clear lateral S-wave velocity variation in the surface layer, and comparisons to results of the microtremor measurements using an array and horizontal-to-vertical ratio conducted along the seismic survey line show significant similarities to the lateral velocity variation revealed by our 2D inversion. We also examined the effect of this lack of velocity homogeneity on the soil response, and we found that it could play an important role in amplifying the content of the high frequencies.