We analyze temporal variations in the travel times of both P and S waves (Vp and Vs) for 14 months at Toyohashi (central Japan) with a continuously operating vibration source that could efficiently produce both P and S waves. Seismic waves produced by the source, which is called the accurately controlled routinely operated signal system (ACROSS), are recorded by three nearby seismic stations, and the travel time variation at each station is estimated using the transfer function calculated from the recorded data. Long-term variations in Vp and Vs are observed and can be interpreted by the change in fluid saturation and crack density of the subsurface rocks. The variation in fluid saturation and crack density are consistent with that in the groundwater level, which is measured at the station nearest to the ACROSS. Short-term responses to rainfalls are observed at the station nearest to the ACROSS system; the interpretation of the changes in crack density and saturation is inconsistent with the ground water observation, partly owing to the initial response to rainfall. This can be interpreted as an air–water mixture within pores or cracks on a fine scale.

我们分析了丰桥（日本中部）14 个月内 P 波和 S 波（Vp 和 Vs）传播时间的时间变化，该振动源可以有效地产生 P 波和 S 波。震源产生的地震波称为精确控制的常规操作信号系统 (ACROSS)，由附近的三个地震台站记录，每个台站的走时变化使用根据记录数据计算的传递函数进行估计。观察到 Vp 和 Vs 的长期变化，可以通过地下岩石的流体饱和度和裂缝密度的变化来解释。流体饱和度和裂缝密度的变化与地下水位的变化一致，地下水位是在离 ACROSS 最近的站点测量的。在最靠近 ACROSS 系统的站点观察到对降雨的短期响应；对裂缝密度和饱和度变化的解释与地下水观测不一致，部分原因是对降雨的初始反应。这可以解释为细小的孔隙或裂缝中的空气-水混合物。