Abstract
Based on the analysis of 45 seismic reflection profiles, the top of the Ryukyu Arc basement is mapped in the forearc region east of Taiwan. The Ryukyu Arc slope dips 10° trenchward, while beneath the forearc basins, the arc basement shows a series of morphologic along-arc ‘highs-and-lows’. One of the basement highs, the Nanao basement rise, has been described as an area uplifted by the subduction of the Gagua Ridge. The other one, the Hoping basement rise, is suggested in this study to be an uplifted feature caused by the subduction (or the underplating) of some local asperity. The nature of this asperity could either be a detached block of the Luzon Arc, an isolated seamount or some material removed from the frontal part (southernmost extremity) of the Ryukyu margin.From seismic reflection profiles, we infer that the right-lateral transcurrent fault system located at the rear of the accretionary wedge defines the surface projection of the southern termination of the Ryukyu Arc basement. Two crustal sections across the Ryukyu subduction system demonstrate that the backstop terminates in the form of a near-vertical ‘wall’ with its height over 5 km. Such an unusual geometry could be produced by crustal truncation at the toe of the backstop.