Interseismic coupling maps and, especially, estimates of the location of the fully coupled (locked) zone relative to the trench, coastline, and slow slip events are crucial for determining megathrust earthquake hazard at subduction zones. We present an interseismic coupling inversion that estimates the locations of the upper and lower boundaries of the locked zone, the lower boundary of the deep transition zone, and downdip gradient of creep rate in the transition from locked to freely creeping in the downdip transition zone. We show that the locked zone at Cascadia is west of the coastline and 10 km updip of the slow slip zone along much of the margin, widest (25–125 km, extending to ∼19 km depth) in northern Cascadia, narrowest (0–70 km) in central Cascadia, with moment accumulation rate equivalent to a M_w 8.71 and M_w 8.85 earthquake for 300- and 500-year earthquake cycles. We find a steep gradient in creep immediately below the locked zone, indicative of propagating creep, along the entire margin. At Nankai, we find three distinct zones of locking (offshore Shikoku, offshore southeast Kii peninsula, and offshore Shima peninsula) with a total moment accumulation rate equivalent to a M_w 8.70 earthquake for a 150-year earthquake cycle. The bottom of the locked zone is nearly under the coastline for all three locked regions at Nankai and is positioned 0–5 km updip of the slow slip zone. In contrast with Cascadia, creep rate gradients below the locked zone at Nankai are generally gradual, consistent with stationary locking.

中文翻译：

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定位南海和卡斯卡迪亚俯冲带的锁定区和蠕动区之间的边界


地震间耦合图，特别是对完全耦合（锁定）带相对于海沟、海岸线和慢滑事件位置的估计，对于确定俯冲带的大推力地震危险性至关重要。我们提出了一个地震间耦合反演，它估计了锁定区的上下边界位置、深过渡区的下边界以及下倾过渡区从锁定到自由蠕变过渡中蠕变速率的下倾梯度。我们表明，卡斯卡迪亚的锁定带位于海岸线以西，沿大部分边缘的慢滑带向上倾斜 10 公里，卡斯卡迪亚北部最宽（25-125 公里，延伸至 ∼19 公里深度），卡斯卡迪亚中部最窄（0-70 公里），在 300 年和 500 年地震周期中，矩累积速率相当于 M_w 8.71 和 M_w 8.85 地震。我们发现锁定区正下方的蠕变有一个陡峭的梯度，表明沿整个边缘传播蠕变。在南海，我们发现了三个不同的锁定带（四国近海、纪伊半岛东南近海和志摩半岛近海），其总力矩累积率相当于 150 年地震周期的 M_w 8.70 地震。锁定区的底部几乎位于南海所有三个锁定区域的海岸线下方，位于慢滑带上倾 0-5 公里处。与 Cascadia 相比，Nankai 锁定区以下的蠕变速率梯度通常是渐进的，与稳态锁定一致。