[S-GD01] Geodetic Advances in Crustal Dynamics and Environmental Change for Taiwan and Neighboring Regions

[SGD01-P03] GPS/Acoustic Seafloor Geodetic Observation off Hualien, Taiwan

*Yi-Lin CHIANG¹、Horng-Yue Chen¹、YA-JU HSU¹、Ryoya Ikuta²、HSIN TUNG¹ (1. Institute of Earth Sciences, Academia Sinica、2.Shizuoka University)

キーワード：Seafloor geodesy, GNSS-Acoustic

Taiwan is bounded by the Ryukyu and Manila subduction zones, where the southern Ryukyu subduction zone accommodates a rapid plate convergence rate of 9–12 cm/yr, posing significant seismic and tsunami hazards. While onshore GNSS networks provide valuable geodetic constraints, they lack resolution for capturing shallow fault slip behaviors. Seafloor geodesy using GNSS-acoustic techniques enables precise monitoring of offshore crustal deformation, improving our understanding of subduction dynamics.
We analyze a decade of GNSS-acoustic data from the OHUA site, 60 km east of Taiwan, near the Okinawa Trough back-arc basin. Since 2014, surveys have been conducted 1–3 times per year using a transponder array at 3600 m depth. A drifting measurement strategy has reduced acoustic noise by 30%, significantly enhancing positioning accuracy. Recent results indicate a southward motion of 65 ± 5.5 mm/yr, eastward displacement of 14 ± 5.83 mm/yr, and vertical displacement of -0.3 ± 5.79 mm/yr, highlighting active deformation near the subduction interface. These findings suggest ongoing strain accumulation that may influence future seismic activity, emphasizing the importance of long-term seafloor geodetic monitoring in assessing offshore earthquake hazards.