Pronounced temporal velocity variations within the fault fracture zone in response to Earth tide modes.

Continuous monitoring of seismogenic faults can advance our understanding of the evolution process, holding important keys for forecasting future earthquakes. We report here seismic velocity variations around the Anninghe fault zone in southwest China based on seismic interferometry techniques. We observed that tidal forces significantly impact velocity changes within the fault fracture zone, inducing periodic changes in seismic velocity on diurnal, semidiurnal and monthly scales. Moreover, the response to Earth tides is notably more pronounced in the fault fracture zone compared to other areas. This can be attributed to tidal forces affecting the opening and closing of cracks in the subsurface medium. Due to the higher density of fractures within the fault fracture zone, it becomes more sensitive to tidal forces. Our findings underscore the crucial role of tidal forces in perturbing stress within the fault zone during periods when earthquakes have not occurred.