Observing Earthquake-Induced Velocity Change on the Rock Slope Following the 2021 M 7.4 Maduo Earthquake 780 km Away

Velocity changes (dv/v) during and after earthquakes are important indicators for understanding the earthquake-induced mechanical damage evolution of rock slopes. However, studying slope responses associated with various seismic loading still remains challenging due to limited in situ observations. In this article, we conduct a 20 min temporal resolution monitoring of dv/v at the frequency band between 2 and 20 Hz by applying ambient noise interferometry on the Pubugou rock slope in Southwest China. We observe an instantaneous similar to 0.41% dv/v drop on the slope caused by the 2021 M 7.4 Maduo earthquake at a distance of 780 kM, following a characterized logarithmic recovery process of similar to 31.39 h towards its pre-earthquake state. Moreover, the dv/v in five narrow frequency bands show a similar drop and subsequently increased recovery times associated with the deceased frequencies due to the long-distant earthquake shaking. We discuss two possible mechanisms related to the heterogeneous rock slope excited by the long-distant earthquake at a low frequency. The study motivates the damage assessment of the rock slope using in situ dv/v and furthers the understanding of subsurface geological risks under diverse seismic loadings.