Controls on plate motion by oscillating tidal stress: Evidence from deep tremors in western Japan

Abstract

Deep tremors are considered to be shear slip on the plate interface and are often sensitive to tidal stress. Here we demonstrate that a small cluster of tremors is extremely well correlated with tide levels observed at nearby stations in western Japan. The correlation is interpreted as representing a nonlinear relationship between stress and slip, which is similar to the rate-dependent friction law. An empirical relationship and observed tide records explain the temporal changes in tremor activity over 9 years. The combination of the nonlinear fault rheology and oscillating tidal stress may control temporal changes in plate motion and earthquake occurrence. Remarkably, the background seismicity is similar to the predicted tremor rate obtained from tidal observations over the past 50 years. This mechanism may also explain the seasonality and decadal-scale weak periodicity of large earthquakes and is likely to be helpful in probabilistic forecasting of future seismicity.