海底地殻変動観測データとマルコフ連鎖モンテカルロ法に基づく南海トラフ浅部での複数のスローイベントの検出

抄録

Slow earthquakes, which consist of low-frequency earthquakes, tremors, and slow slip events (SSEs), have occurred at the Nankai Trough subduction zone in southwestern Japan. Among others, long-term SSEs at deeper parts of the locked zone on the subduction plate interface had been detected by onshore GNSS array. Nowadays, thanks to development of seafloor GNSS-A measurement, we have been able to estimate long-term SSEs at a shallow part of the subduction zone. Here we try to detect slow events along the Nankai Trough, using a Markov Chain Monte Carlo method which does not assume a fixed duration of unsteady displacement. We find six observation points with unsteady displacement, and interpret that four types of slow events with various periods occurred. One point experienced a very long-term (over three years) undefined, probably a landslide-like event. Another point might be influenced by previously-reported very-low-frequency earthquakes. Another point moved due to a SSE found by onshore GNSS array. For the other three points, the unsteady displacement represented a shallow SSE near the trench as proposed by a recent study.