17:15 〜 18:45
[SCG47-P05] Seawater radon concentration in relation to submarine active faults and the seismicity in the Yatsushiro Sea, Japan
キーワード：八代海底活断層、ラドン濃度、地震、八代海
We investigated the relationship between radon (222Rn) concentrations in seawater and crustal activity in the Yatsushiro Sea by studying the submarine fault zone. Yatsushiro submarine faults are located at the southern end of the Futagawa-Hinagu fault zone, which was activated by the 2016 Kumamoto earthquake (Mw 7.0). We analyzed the 222Rn concentration in samples of bottom water just above the seafloor, and pore water in sediments, obtained using Multiple and Piston cores of the Hakuho Maru Expedition KH18-3 (July 27-30, 2018).
Typically, 222Rn is rarely detected in seawater. However, we observed higher 222Rn concentrations around the middle sites in the Yatsushiro Sea. Sediments around these sites are quasi-homogeneous, which primarily consist of sand and mud. 222Rn from river water is negligible around the area. For crustal activity, higher-stress field and dense active faults are reported around the sites. Seismic analysis show that the high 222Rn concentration regions align with the area seismically most active. Seismicity analysis also revealed high moment release and a low b-value after the 2016 Kumamoto earthquake around the region, indicating increased seismic activity and potential for large earthquakes around the Yatsushiro Sea.
Our results suggest that heightened concentrations of 222Rn in seawater can serve as an effective tracer for estimating submarine fault activity. This study highlights the usefulness of 222Rn concentrations in the detection of submarine active faults and activity assessment and contributes to the understanding of the potential for future large earthquakes in the Yatsushiro Sea.
Typically, 222Rn is rarely detected in seawater. However, we observed higher 222Rn concentrations around the middle sites in the Yatsushiro Sea. Sediments around these sites are quasi-homogeneous, which primarily consist of sand and mud. 222Rn from river water is negligible around the area. For crustal activity, higher-stress field and dense active faults are reported around the sites. Seismic analysis show that the high 222Rn concentration regions align with the area seismically most active. Seismicity analysis also revealed high moment release and a low b-value after the 2016 Kumamoto earthquake around the region, indicating increased seismic activity and potential for large earthquakes around the Yatsushiro Sea.
Our results suggest that heightened concentrations of 222Rn in seawater can serve as an effective tracer for estimating submarine fault activity. This study highlights the usefulness of 222Rn concentrations in the detection of submarine active faults and activity assessment and contributes to the understanding of the potential for future large earthquakes in the Yatsushiro Sea.