[S-CG44] Science of slow-to-fast earthquakes

[SCG44-P15] Gravity observations in long-term slow slip areas in Japan

*田中 愛幸¹、坂上 啓¹、平松 祐一¹ (1.東京大学理学系研究科)

キーワード：スロー地震、スロースリップ、重力、間隙流体、地殻変動、水

The water in Earth’s mantle is closely related with plate subduction and volcanism. Recent studies revealed that the mantle wedge corner at approximately 30 km depth holds high-pressure water, where slow earthquakes occur. To quantify how such water behaves during slow earthquakes helps understand the mechanisms of these earthquakes and (eventually) a part of the long-term water cycle between the interior and surface of the Earth. However, little evidence has been reported on the transient flows of such deep water. In a previous study, we reported anomalous gravity anomalies during two long-term slow slip events in the Tokai area in Japan, which were detected by absolute gravity measurements over 20 years. We presented a poroelastic fluid flow model assuming a localized deformation within the fault fracture zone. The model could reproduce the gravity change with a permeability range between those suggested by laboratory experiments and numerical simulations of slow earthquakes. Similar observations using absolute and relative gravimeters have been performed in the long-term slow slip areas along the Nankai Trough and the Ryukyu Trench. In this poster, we will introduce gravity observations at these sites.