Slipping the Shumagin Gap: A Kinematic Coseismic and Early Afterslip Model of the Mw 7.8 Simeonof Island, Alaska, Earthquake
Slipping the Shumagin Gap: A Kinematic Coseismic and Early Afterslip Model of the Mw 7.8 Simeonof Island, Alaska, Earthquake
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DOI：
10.1029/2020gl090308
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发表时间：
2020-10-16
影响因子：
5.2
通讯作者：
Melgar, Diego
中科院分区：
文献类型：
--
作者：
Crowell, Brendan W.;Melgar, Diego
2020年7月，阿拉斯加半岛近海Simeonof岛以东直接发生7. 8级地震。这次地震使舒马金缺口东部破裂，该地区在过去世纪没有发生过大地震，大地耦合度低。在这里，我们调查的破裂运动学的地震使用联合反演的高速率GNSS和强震数据。我们发现，破裂集中在30-45公里的深度之间，从Shumagin群岛以东开始，向西北方向下倾破裂，在西经160度以西几乎没有滑动。早期的地震后观察表明，深度在40-60公里之间的整个舒马金峡因无震余震和余震而破裂。从历史上看，这场地震与1917年的舒马金群岛地震相似，表明可能存在破裂粗糙体，以解释与7. 5 -8级地震相似的低震间耦合和重复。简明语言摘要2020年7月，阿留申群岛靠近俯冲带未锁定部分的舒马金缺口（Shumagin Gap）发生了一次7. 8级大地震。完全锁定的断层更容易发生大地震，因为变形不会随着时间的推移缓慢释放。我们使用附近位移和速度的观测来模拟地震是如何滑动的。我们发现，2020年7月的地震主要破裂了俯冲带的解锁部分，并没有破裂到高度锁定的区域。这种特殊的滑动模式在1917年也曾出现过，这表明该地区断层带的结构可能有利于地震，并且正在发生一些震间锁定，以允许每世纪发生一次7.5 -8级地震。
In July 2020, a Mw 7.8 earthquake initiated directly to the east of Simeonof Island offshore of the Alaska Peninsula. The earthquake ruptured the eastern part of the Shumagin Gap, a region devoid of large earthquakes over the last century and characterized by low geodetic coupling. Here, we investigate the rupture kinematics of the earthquake using a joint inversion of high-rate GNSS and strong-motion data. We find that the rupture was focused between depths of 30-45 km, starting east of the Shumagin Islands and rupturing downdip towards the northwest, with little slip west of 160 degrees W. Early postseismic observations indicate that the entirety of the Shumagin Gap at depths between 40-60 km ruptured with aseismic afterslip and aftershocks. Historically, this earthquake resembles the Shumagin Islands earthquake of 1917, indicating that a possible rupture asperity exists to explain low interseismic coupling and repeating similar to M7.5-8 earthquakes.Plain Language Summary A large Mw 7.8 earthquake occurred in July 2020 in the Aleutian Islands near a part of the subduction zone that is not locked, the Shumagin Gap. A fully locked fault will be more susceptible to large earthquakes since deformation is not released slowly over time. We model how the earthquake slipped using both observations of displacement and velocity nearby. We find that the July 2020 earthquake ruptured mainly the unlocked portion of the subduction zone and did not rupture into regions that are highly locked. This peculiar pattern of slip was also seen previously in 1917, indicating that the structure of the fault zone in the area may be conducive to earthquakes and some interseismic locking is occurring to allow for M7.5-8 earthquakes every century.