The potential for a great earthquake along the southernmost Ryukyu subduction zone

Interseismic GPS data along the Hualien-Suao coast (NE Taiwan) shows a pattern of strain accumulation that is consistent with a potential future large shallow earthquake along the southernmost Ryukyu subduction zone. The measured shortening rate parallel to the Ryukyu Trench is 80 mm/yr, about twice of the shortening rate perpendicular to the Ryukyu Trench. We invert for slip-deficit rates and the geometric configuration of the plate interface. Our preferred fault model dips 10 degrees northward and extends about 70 km from the Ryukyu Trench to a depth of 13 km. The slip-deficit rate exhibits a left-lateral motion of 78 mm/yr and a normal motion of 36 mm/yr on a 290 degrees-trending fault. The slip rate budget of the southernmost Ryukyu subduction zone is close to the plate convergence rate, suggesting the plate interface is fully locked. Assessments of seismic hazard in this region need to consider the potential threat from M-w 7.5 similar to 8.7 tsunami earthquakes generated by shallow ruptures.