Earthquake Science Center, U.S. Geological Survey, Moffett Field, CA, USA.
National Earthquake Information Center, Geological Hazards Science Center, U.S. Geological Survey, Golden, CO, USA.
Sci Adv. 2023 Apr 28;9(17):eadf9299. doi: 10.1126/sciadv.adf9299. Epub 2023 Apr 26.
The shallower portions of subduction zone megathrust faults host Earth's most hazardous tsunamigenic earthquakes, yet understanding how and when they slip remains elusive because of challenges making seafloor observations. We performed Global Navigation Satellite System Acoustic seafloor geodetic surveys before and ~2.5 months after the 29 July 2021 (moment magnitude) 8.2 Chignik, Alaska, earthquake and determine ~1.4 meters cumulative co- and post-seismic horizontal displacement ~60 kilometers from the megathrust front. Only for the 2011 9 Tohoku event have closer subduction zone earthquake displacements been observed. We estimate ~2 to 3 meters of megathrust afterslip shallower than 20 kilometers, a portion of the megathrust on which both inter- and co-seismic slip likely had occurred previously. Our analysis demonstrates that by 2.5 months, shallower and deeper moment had effectively equilibrated on the megathrust, suggesting that its tsunamigenic potential remains no more elevated than before the earthquake.
俯冲带浅部的走滑断层是地球上最危险的海啸成因地震的震源，但由于在海底进行观测存在挑战，因此仍然难以理解它们是如何以及何时发生滑动的。我们在 2021 年 7 月 29 日（矩震级）8.2 级的阿拉斯加钦尼克地震发生前和大约 2.5 个月后进行了全球导航卫星系统（GNSS）声学海底大地测量调查，确定了在距走滑断层前缘约 60 公里处的水平累积共位移和震后位移约 1.4 米。只有在 2011 年的 9 级东日本地震中，人们才观察到更靠近俯冲带的地震位移。我们估计，在 20 公里以下的浅部区域，有 2 到 3 米的走滑断层发生了余滑，这部分走滑断层可能之前已经发生过震间和共震滑动。我们的分析表明，到 2.5 个月时，浅层和深层地震矩已经在走滑断层上有效平衡，这表明其海啸潜力与地震前相比并没有更高。
