[S-CG40] Science of slow-to-fast earthquakes

[SCG40-31] Detailed spatio-temporal comparison of SSE slip and tremor activities in the Nankai subduction zone

*矢部 優¹、落 唯史¹、松本 則夫¹、松澤 孝紀² (1.産業技術総合研究所、2.防災科学技術総合研究所)

キーワード：スロー地震、スロースリップ、微動

Slow earthquakes include broadband signals from tectonic tremors or low frequency earthquake (LFEs) in 2 – 8 Hz to slow slip events (SSEs) in geodetic frequency band. Those signals are usually collocated both in space and time, but not always. For example, SSEs migrate continuously over Ise Bay, whereas tremors are not detected there. We need to reveal detailed spatio-temporal distributions of tremors and SSEs and compare them in order to understand broadband characteristics of slow earthquakes. Spatio-temporal distributions of tremors and LFEs have been investigated well because high-frequency signals have good spatio-temporal resolutions. On the other hand, SSEs usually smaller than Mw 6.4 was difficult to investigate their detailed spatio-temporal slip distributions. We developed a joint inversion method for slip distributions of SSEs using three types of geodetic data (GNSS, tilt, and strain). As tilt and strain data used are sampled every 1 hour, we can estimate slip distributions with better temporal resolutions than the inversion usually conducted only with GNSS. We applied to data for SSE in November 2022 at western Shikoku region. The revealed spatio-temporal distributions of SSE slip generally show good agreement with LFE activities, though there are also separations between them. SSE slip and LFEs are initiated almost at the same time, whereas SSE slip cannot be detected at the final phase of LFE activities, where LFEs are modulated by tidal stress. In this presentation, we will report the detailed comparisons between SSE slip and LFE activities.