Complex Interaction, Striations, and Periodicity of Deep Tremor Surrounding a Tremor Gap in the Central Nankai Subduction Zone, Japan

Abstract

AbstractThe Nankai subduction zone is characterized by a belt of deep tremor extending from western Shikoku to the Tokai region and a tremor seismicity gap beneath the Kii Channel between Shikoku and the Kii Peninsula. Tremor activities near the gap are not well understood because of poor seismic network coverage. In this study, we conducted an observation campaign in eastern Shikoku to investigate the detailed tremor activity across the tremor gap. The new tremor catalog shows high detectability and resolution, with tremor clusters in both eastern Shikoku and the western Kii Peninsula having distinct shapes. We discovered characteristic time intervals between tremor activity on both sides of the gap, suggesting the occurrence of undetected slow slip events (SSEs) within the gap that propagated approximately 10 km/day. We also found a relationship between the tremor activities and a shallower long‐term SSE. Our examination of the detailed distribution of tremor events showed a distinct striation pattern that may be associated with the history of the subducting plate motion and the plate geometry, and our examination of their periodicity showed spatial variations in the dominant period of tremor activity that likely reflect the heterogeneous physical properties of the plate interface.