In March and May 2021, Mw7.0 and Mw6.7, respectively, deep interplate earthquakes occurred off Miyagi, Japan, near the downdip edge of the rupture area of the 2011 M9 Tohoku earthquake. We study the two Mw ∼ 7 earthquakes to investigate how a great (Mw ∼ 9) earthquake cycle impacts the generation of smaller (Mw7-8) earthquakes in the deep seismic/aseismic transition zone. Our hypocenter relocation results show that many repeating earthquakes have emerged in the downdip area after the Tohoku earthquake. The March Mw7.0 event was initiated in the slip area of an emerging interplate repeating earthquake sequence, suggesting that the nucleation of the Mw7.0 event occurred in a conditionally stable area where only aseismic slip occurred before the Tohoku earthquake. Downdip high-rate creep in the postseismic period is a probable reason for the temporal aseismic-to-seismic transition that allowed the occurrence of repeating earthquakes and the rupture initiation of the Mw7.0 earthquake. The May Mw6.7 earthquake originated in an area where earthquake activity was high locally, both before and after the Tohoku earthquake, and shear stress increased after the March event. This suggests that both frictional properties and shear stress change contributed to the rupture initiation. The slip inversion results indicate that these two Mw ∼ 7 earthquakes ruptured the western part of the 1978 Mw7.6 Miyagi-Oki earthquake source area and loaded the eastern part. Continued monitoring of seismicity patterns, including possible updip expansion of the interplate seismicity, is essential to examine how strain energy, plate-locking state, and creep evolve during the Mw9.0 earthquake cycle.

中文翻译：

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2021 Mw7.0 和 Mw6.7 Miyagi-Oki 地震在深地震/抗震过渡区成核：2011 年东北地震可能造成的瞬态不稳定影响

2021 年 3 月和 5 月，分别在 2011 年 M9 东北地震破裂区的下倾边缘附近，日本宫城附近发生了 Mw7.0 和 Mw6.7 深部板间地震。我们研究了两次 Mw ∼ 7 地震，以研究一个大 (Mw ∼ 9) 地震周期如何影响深地震/抗震过渡带中较小 (Mw7-8) 地震的产生。我们的震源重定位结果表明，东北地震后下倾区出现了多次重复地震。3 月 Mw7.0 事件开始于新出现的板间重复地震序列的滑动区，表明 Mw7.0 事件的成核发生在东北地震前仅发生抗震滑动的条件稳定区。震后时期的下倾高速蠕变可能是导致地震反复发生和 Mw7.0 地震破裂的时间性地震-地震过渡的可能原因。5 月 Mw6.7 地震起源于东北地震前后局部地震活动高的地区，3 月事件后剪应力增加。这表明摩擦特性和剪切应力变化都促成了破裂的开始。滑动反演结果表明，这两次Mw∼7地震使1978年Mw7.6宫城-冲震震源区的西部破裂，并对东部产生负荷。继续监测地震活动模式，包括可能的板间地震活动的上倾扩展，对于检查应变能、