Wide-area seismicity anomalies before the 2011 Tohoku–Oki earthquake

Abstract

Summary This study investigates various types of seismicity changes that occurred in several regions in and around the Tohoku District, prior to the 2011 M9.0 Tohoku–Oki earthquake. In particular, we focus on the seismicity anomalies that were revealed not only in inland local areas but also in a wide area for several years before the 2008 M7.2 earthquake in the inland Tohoku District. We reconsider these seismicity anomalies in nearly identical regions, which persisted in the extended period up until the M9 mega event. This suggests that the stress changes due to transient slow slips on the Pacific Plate boundary are more likely to be the cause of the wider seismicity changes than the slips beneath the inland earthquake. To confirm the significance, we use the two-stage stationary epidemic-type aftershock sequence model and explore the relationship between seismicity changes and stress rate changes due to slow slip by means of global navigation satellite system geodetic observations.