Tsunami sediments

一些俯冲带与大地震有关，而另一些则不频繁或罕见。琉球俯冲带属于伸展带，具有最快的会聚速度(12.5厘米/年)。在这个俯冲带，我们获得了一套完整的海啸层，发现它们埋藏在一个缓坡小山中。最近的事件对应于几个记录中记录的1771年事件。记录到的高度为20米，而最高的海啸层达到8米，这与历史文献非常一致，因为海啸的沉积物低于海水的上升高度。据估计，1771年地震发生在断层滑动20m的海沟附近，如果其相对板块运动100%累积，则该滑动可累积160年。然而，我们发现的间隔是500年，甚至可能是100年，比这次滑动的时间要长得多。这表明伸展俯冲带在其界面上存在无效的滑移堆积。

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 The height documented is 20 m while the highest tsunami layer reaches to 8 m, which are very consistent with historical documents since tsunami sediments below the run-up heights of sea water.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.