The Nankai Trough, Japan, is a subduction zone characterized by the recurrence of disastrous earthquakes and tsunamis. Slow earthquakes and associated tremor also occur intermittently and locally in the Nankai Trough and the causal relationship between slow earthquakes and large earthquakes is important to understanding subduction zone dynamics. The Nankai Trough off Muroto, Shikoku Island, near the southeast margin of the rupture segment of the 1946 Nankai earthquake, is one of three regions where slow earthquakes and tremor cluster in the Nankai Trough. On the Philippine Sea plate, the rifting of the central domain of the Shikoku Basin was aborted at ~15 Ma and underthrust the Nankai forearc off Muroto. Here, the Tosa‐Bae seamount and other high‐relief features, which are northern extension of the Kinan Seamount chain, have collided with and indented the forearc wedge. In this study, we analyzed seismic reflection profiles around the deformation front of accretionary wedge and stratigraphically correlated them to drilling sites off Muroto. Our results show that the previously aborted horst‐and‐graben structures, which were formed around the spreading center of the Shikoku Basin at ~15 Ma, were rejuvenated locally at ~6 Ma and more regionally at ~3.3 Ma and have remained active since. The reactivated normal faulting has enhanced seafloor roughness and appears to affect the locations of slow earthquakes and tremors. Rejuvenated normal faulting is not limited to areas near the Nankai Trough, and extends more than 200 km into the Shikoku Basin to the south. This extension might be due to extensional forces applied to the Philippine Sea plate, which appear to be driven by slab‐pull in the Ryukyu and Philippine trenches along the western margin of the Philippine Sea plate.

中文翻译：

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菲律宾海板块的年轻化延伸及其对南海海槽俯冲动力学的影响

日本的南海海槽是一个俯冲带，其特征是灾难性地震和海啸的再次发生。慢地震和相关的震颤在南开海槽中也间歇性和局部发生，慢地震和大地震之间的因果关系对于理解俯冲带的动力学很重要。四国岛室户町附近的南海海槽位于1946年南海地震破裂段的东南边缘附近，是南海海槽缓慢地震和震群聚集的三个地区之一。在菲律宾海板上，四国盆地中部的裂谷在〜15 Ma时中止，并在室户附近的南海前臂下推。这里是Tosa-Bae海山和其他高浮雕特征，它们是Kinan Seamount链的北部延伸，与前楔碰撞并缩进。在这项研究中，我们分析了增生楔形变形前沿周围的地震反射剖面，并将其与Muroto以外的钻探地层进行了地层相关。我们的结果表明，在四国盆地扩散中心周围约15 Ma处形成的先前垂死的霍斯特-格拉本结构在约6 Ma处局部恢复了活力，而在约3.3 Ma处则更局部地恢复了活力，此后一直保持活跃。重新激活的正常断层增加了海底粗糙度，并似乎影响了慢地震和震颤的位置。再生的正常断层不仅限于南海海槽附近，而且向南延伸到四国盆地超过200公里。这种延伸可能是由于施加在菲律宾海板块上的延伸力所致，