The shaking we feel during an earthquake is caused by the movement of the ground due to seismic waves. These waves are measured using three-component seismometers: east-west, north-south, and up-down. The obtained data can be analyzed as the behavior of particles placed at specific points. This analysis is useful in extracting more information in research areas such as underground resource development. However, time-frequency domain analysis, which is good at capturing small signals, can only handle the vertical oscillations of the first arriving P-wave due to the limitations of mathematical description, making it difficult to extract the planar S-wave oscillations.
A research group led by Assistant Professor Yusuke Mukuhira from the Institute of Fluid Science at Tohoku University, and Professor Taku Nonomura from the Graduate School of Engineering at Nagoya University, focused on a time-delay component analysis used in the field of fluid dynamics. By introducing a time-delay component into the particle analysis, the group has developed a signal processing technique that allows evaluation of precise characteristics of seismic motion. They tested this technique using synthesized data and applied it to microseismic data obtained in an actual underground resource field as well as natural seismic data including later phases. As a result, this technique allowed to characterize planar polarization waves such as S waves and detect P waves and later phases with small amplitudes.
These results are expected to be applied to monitoring not only in seismology but also in fields where it is difficult to install multiple observation points, such as planetary exploration and underground storage of carbon dioxide. In connection with this research, progress is being made in detecting P waves and S waves and locating hypocenters of microearthquakes from underground resource development. In the future, the researchers aim to contribute to the extraction and understanding of various phenomena from the vast amount of time series data that is difficult to analyze visually.
