Seismic supercycles in the Ryukyu islands: a multi-temporal study.

Speaker: Sophie Debaecker (ERI)

Abstract:
The Ryukyu subduction zone, located between Japan main island and Taiwan, has not shown any major megathrust earthquake for at least 250 years. Is it steadily creeping? Or at the contrary, is it loading strain that could be suddenly released? We turned to different tools to investigate this subduction zone behavior and history at long, mid, short and very short-terms.
We studied the geomorphology of the whole island arc using very-high resolution satellite imagery. We measured several marine terraces and estimated vertical motion of the islands over several hundred of thousand years. We sampled and analyzed coral microatolls in the southern Ryukyus to retrieve variations of the relative sea-level over decades to millenia. This complete the work achieved by Weil-Accardo et al. (2020) in the central Ryukyus. Finally, adding GPS data, we discuss possible links between our different observations through the characterization of seismic supercycles.