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

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

*Yoshiyuki Tanaka¹, Hiromu Sakaue¹, Yuichi Hiramatsu¹ (1.Earth and Planetary Science, The University of Tokyo)

Keywords:slow earthquakes, slow slip, gravity, pore fluid, crustal deformation, water

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.