On the landward slope of the Japan Trench, the mid-slope terrace (MST) is located at a depth of 4000–6000 m. Two piston cores from the MST were analyzed to assess the applicability of the MST for turbidite paleoseismology and to find out reliable recurrence record of the great earthquakes along the Japan Trench. The cores have preserved records of ~ 12 seismo-turbidites (event deposits) during the last 4000 years. In the upper parts of the two cores, only the following earthquakes (magnitude M ~ 8 and larger) were clearly recorded: the 2011 Tohoku, the 1896 Sanriku, the 1454 Kyotoku, and the 869 Jogan earthquake. In the lower part of the cores, turbidites were deposited alternately in the northern and southern sites during the periods between concurrent depositional events occurring at intervals of 500–900 years. Considering the characteristics of the coring sites for their sensitivity to earthquake shaking, the concurrent depositional events likely correspond to a supercycle that follows giant (M ~ 9) earthquakes along the Japan Trench. Preliminary estimations of peak ground acceleration for the historical earthquakes recorded as the turbidites imply that each rupture length of the 1454 and 869 earthquakes was over 200 km. The earthquakes related to the supercycle have occurred over at least the last 4000 years, and the cycle seems to have become slightly shorter in recent years. Earthquakes off the Sanriku coast forming the alternative deposition of turbidites in the two cores have released a part of accumulated slip, as indicated by the turbidites deposited in only one core. Decreases in the release of accumulated slip have possibly caused the recent shortening of the supercycle.

中文翻译：

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在过去的4000年中，日本海沟沿岸发生大地震的超级循环

在日本海沟的陆坡上，中坡阶地（MST）位于4000-6000 m的深度。对MST的两个活塞芯进行了分析，以评估MST在浊积岩古地震学中的适用性，并找出日本海沟大地震的可靠复发记录。在过去的4000年中，岩心保存了约12个地震浊积岩（事件沉积）的记录。在两个核心的上部，仅清楚记录了以下地震（M级至8级及更大）：2011年东北，1896年三陆，1454年京都大地震和869年Jogan地震。在岩心下部，在同时发生的沉积事件之间，每隔500-900年发生一次，在北部和南部地区，浊积石交替沉积。考虑到取芯部位对地震震动的敏感性，同时发生的沉积事件可能对应于沿日本海沟发生的特大（M〜9）地震之后的超级循环。记录为浊度的历史地震的峰值地面加速度的初步估计表明1454和869级地震的每次破裂长度都超过200 km。与超级周期有关的地震至少在最近4000年中就已发生，并且周期似乎在最近几年略短了。Sanriku海岸附近的地震在两个岩心中形成了混浊的交替沉积，释放出一部分积聚的滑移，正如仅在一个岩心中沉积的混浊物所表明的那样。