Ground water-induced changes in velocities of P and S waves (Vp and Vs) measured using an accurately controlled seismic source

Earth, Planets and Space

Rina Suzuki¹  Koshun Yamaoka¹  Shuhei Tsuji¹  Toshiki Watanabe¹ 

[1] Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan;

关键词: Seismic velocity change;    Artificial seismic source;    ACROSS;    Fluid saturation;    Ground water level;   

DOI  :  10.1186/s40623-021-01484-3

来源: Springer

【 摘 要 】

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.

【 授权许可】

CC BY