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Monitoring Seafloor Deformation in Taiwan via Ocean-bottom Geodetic Instrumentation

Description: 

Taiwan is situated at the complex junction of the Ryukyu and Manila subduction zones, where intense seismic activity is driven by rapid plate convergence. Based on regional geodetic data and tectonic models, the convergence rate along the southern Ryukyu margin exhibits a significant eastward increase, from 92 mm/yr offshore Hualien to 123 mm/yr near the Gagua Ridge, suggesting a high potential for M_w 7.5-8.4 earthquakes. To directly monitor these offshore processes and quantify long-term strain accumulation, we established a GNSS-Acoustic (GNSS-A) network, including six sites along the southern Ryukyu subduction zone. During this continuous monitoring period, the 2024 M_w 7.3 Hualien earthquake occurred, providing a rare opportunity to capture seafloor coseismic signals. At site ORY2, located 40 km east of the epicenter, we recorded a significant coseismic uplift of 52.9 ± 13.5 cm. These observations align with coseismic dislocation modeling and underscore the vital role of offshore fault systems in regional strain release. Furthermore, our long-term monitoring identified multiple slow slip events (SSEs) that preceded the 2024 Hualien earthquake, suggesting a potential mechanical link between transient slip and major rupture initiation.

Offshore southern Taiwan, where three additional GNSS-A sites were established near the northern tip of the Manila Trench, the geodetic data reveal N-S-oriented extension in the Tainan Basin and NE-SW extension between the Manila Trench and the North Luzon Trough. We also observe a distinct shift in deformation patterns across the continent-ocean boundary near 20°N. By integrating these seafloor observations with terrestrial geodesy, this research provides new insights into fault segmentation and plate boundary processes in the Western Pacific. Our results demonstrate that sustained ocean-bottom instrumentation is indispensable for accurately characterizing subduction dynamics and assessing regional seismic and associated hazards.

Session: Linking Subduction Zone Processes and Cascading Hazards in Alaska, Cascadia, Chile and Beyond [Poster]

Type: Poster

Date: 4/16/2026

Presentation Time: 08:00 AM (local time)

Presenting Author: Hsin Tung

Student Presenter: No

Invited Presentation: 

Poster Number: 135

Authors