Long-term slow slip events along the Nankai trough delayed by the 2016 Kumamoto earthquake, Japan

Abstract

Abstract The Global Navigation Satellite System network in Japan detected transient crustal deformation along the Nankai trough, Japan, from June 2018. Time-dependent inversion analysis shows that a long-term slow slip event in northern Hyuga-nada Sea along the Nankai trough, Japan, started in June 2018 and decayed in October 2018. From October 2018, a slip area appeared in the Bungo channel and expanded to northern Hyuga-nada Sea and southwest Shikoku at the time of the maximum slip rate. The slip area in the middle of the Bungo channel started to abate around May 2019, with the slip in neighboring areas nearly stopping in August 2019. The estimated rupture propagation is different from those in the past Bungo channel SSEs, in which rupture propagated southwestward from the Shikoku side to the Kyushu Island side at the time of the maximum slip rate. Furthermore, the rupture in northern Hyuga-nada Sea preceded the Bungo channel SSE and reappeared together with the Bungo channel SSE at the time of the 2018–2019 event, though the northern Hyuga-nada Sea SSE followed the 2009–2011 Bungo channel SSE. There is a possibility that the differences in the rupture propagation and recurrence interval from the past events are due to the 2016 Kumamoto earthquake. The adjacent locked area along the Nankai trough subduction zone is a well-known seismic gap and the 2018–2019 SSE changed the stress state in favor of the occurrence of nearby subduction earthquakes.

Keywords

• Slow slip event
• Hyuga-nada Sea
• Bungo channel