Tsunami sediments

点击翻译按钮获取中文摘要

Some subduction zones are associated with large earthquakes but others are not or infrequent The Ryukyu subduction zone is grouped into the extensional group, having the fastest convergence rate (12.5cm/y). In this subduction zone, we obtained a complete set of tsunami layers which were found to be buried in a gentle slope hill. The most recent event corresponds to the 1771 documented in several records. The height documented is 20 m while the highest tsunami layer reaches to 8 m, which are very consistent with historical documents since tsunami sediments below the run-up heights of sea water. The 1771 event was estimated to have occurred near the trench with a fault slip of 20 m. This slip can be accumulated in 160 years if 100% of its relative plate motion is accumulated. However, the intervals we found are 500 and possibly 100 years, significantly longer that this slip. This suggests that the extensional subduction zone has an ineffective accumulation of slip on its interface.