地震動観測による地震波速度と岩石物性試験による弾性波速度の関係

—段発発破波形の相関による地震波速度構造推定—

抄録

We studied the differences between the velocities of seismic waves and elastic waves in rock core samples to understand the spatial-scale effect of heterogeneous contents. The wave velocities determined from seismic observations and rock property tests of rock core sample are different in most cases. These variations are caused by the difference in the spatial scales of each measurement (i.e., the differences in wave lengths), since the waves refer to the corresponding scales and velocities of heterogeneity in the propagating medium. In order to estimate the seismic wave velocities with very short baselines (∼100 m) by "multiple blasting", we analyzed the arrival times of initial motion, and conducted waveform correlation analyses to transversal pairs for S-wave. Under the assumption that the seismic wave slowness (1/velocity) is an average value corresponding to the medium comprising homogenous fresh rocks at a small scale and the other heterogeneous components such as cracks at larger scale, we compared the seismic wave velocities with the elastic wave velocities that were measured using the rock core samples taken near the seismometers. Our results verified that parameters related to the medium heterogeneity such as crack density, crack shape, and the water content of the medium can be estimated from velocities comparisons.