LOVE 波分散性から評価した足柄平野とその周辺地域の三次元S波速度構造

抄録

Lateral heterogeneities of S-wave velocity structures in and around Ashigara valley in the west of Kanagawa prefecture, Japan were discussed using the phase velocity dispersion of Love waves. The phase velocities in the frequency range of 0.1 to 0.5Hz were determined using the strong motion records of over 40 in and around Ashigara valley from the east off Izu peninsula earthquake (M_j=5.7) of May 3, 1998. We applied a semblance analysis for determining phase velocities by dividing the observation area into several sub-arrays, which consist of 4 or 5 sites. A clear difference of phase velocity dispersions in a wide frequency range was found between the valley region and the mountain/hill sites that are surrounding the valley. S-wave velocity structure models beneath the sub-arrays were estimated by an inversion technique of the genetic algorithm. The structure models show a laterally complex heterogeneity and two distinctive features. The depth to the basement in the east side of Kouzu-Matsuda fault is shallower than that of the west side. The depth to the layer with S-wave velocity of 1.5km/s in the south of Ashigara valley is deeper than that in the north, however, it is opposite for the depth to the layer with S-wave velocity of 2.4km/s, that is, the south of the valley is shallower than that in the north.