Characteristics of Microtremors On Ground with Discontinuous Underground Structure

Abstract

The characteristics of microtremors are examined, which were observed in an area having underground structures with vertical discontinuities. The work in now going on is made near the eastern edge of the southern part of Kyoto basin. The spatial correlation characteristics of microtremors are significantly affected by the vertical discontinuities of surface-soil layers. The phase velocities of vertical components how the dispersive nature of Rayleigh waves. The microtremors in this area tend to propagate from plain side to hill side, i.e. thick layer side to thin layer one. The tremors of wave length shorter than the thickness of the thin layer seem to be converted to a new mode soon after coming across a vertical discontinuity, but those of sufficiently longer wave lengths seem to sustain the old mode for a longer distance. The lateral variation of the amplitude of microtremors is explained in terms of the transmission and reflection of surface waves at a vertical discontinuity.