Activation of very low frequency earthquakes by slow slip events in the Ryukyu Trench

Long‐term activity of shallow very low frequency earthquakes (VLFEs) in the Ryukyu Trench, unassociated with recent large thrust earthquakes, was analyzed using a broadband seismometer network. The distribution of shallow VLFEs was divided into three large clusters. The activity of the VLFEs is modulated by repetitive slow slip events, and the activity of these VLFEs increases to 2–3 times its ordinary rate at 10–20 days after the onset of the slow slip events. The activation of VLFEs could be generated by small increases on the order of approximately 0.1–0.5 kPa in Coulomb failure stress, suggesting that stress in the plate interface where the VLFEs occur is frequently released in small amounts. Moreover, the distribution of VLFEs is complementary to the historical tsunami source area and locked area. The distribution of the VLFEs indicates heterogeneity in interplate coupling along the trench.