Migration of shallow and deep slow earthquakes toward the locked segment of the Nankai megathrust
Migration of shallow and deep slow earthquakes toward the locked segment of the Nankai megathrust
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DOI：
10.1016/j.epsl.2019.115986
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发表时间：
2020-02
影响因子：
5.3
通讯作者：
N. Uchida;R. Takagi;Y. Asano;K. Obara
中科院分区：
文献类型：
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作者：
N. Uchida;R. Takagi;Y. Asano;K. Obara
南开逆冲构造位于日本四国和九州海域，以各种慢震为特征，这些慢震在板块边界断层上的相对运动比常规地震慢。在该地区，北部（四国近海）的板块间闭锁作用强于南部（九州近海），北部地区多次发生Mw ~ 8级地震（南开地震）。本文在重复地震和慢震分析的基础上，研究了慢震（极低频地震、震颤和慢滑事件）的时空分布，特别关注不同活动之间的相互作用。综合分析2003 - 2016年的地震和大地测量资料，发现南开主锁闭区外35 ~ 50 km深度内各类慢震互补性分布。我们还发现了不同活动之间的相互作用。重复地震与慢震的相互作用表明，重复地震活跃区可分为深部（深度≥20 km）和浅层（深度< 20 km）。对深部重复地震和内陆全球导航卫星系统（GNSS）数据的分析表明，长期慢滑事件（ses）沿板块边界在20-50 km（九州近海）和20-35 km（四国）深度缓慢北移。这些迁移发生在2-3年期间，包括2003年和2010年位于九州和四国之间的本古海峡的大型慢滑事件。分析还显示了浅层重复地震和浅层极低频地震之间的相互作用，这表明在2010年长期慢滑期的一个月时间内，短期地震从九州近海浅层板块边界向四国下方较深地区的北移速度更快。南开特大逆冲地震震源附近~ 300 km范围内的深部缓慢迁移和浅部至深部快速迁移表明南开特大逆冲地震震源周围存在广泛的非稳态应力积累过程。
The Nankai megathrust is located offshore Shikoku and Kyushu, Japan and is characterized by various kinds of slow earthquakes whose relative motions across the plate boundary faults are slower than regular earthquakes. In the area, the interplate locking is stronger in the northern area (offshore Shikoku) than in the southern area (offshore Kyushu) and Mw ∼8 earthquakes (Nankai earthquakes) have occurred repeatedly in the northern area. In this paper, the spatio-temporal distributions of slow earthquakes (very low frequency earthquakes, tremors and slow-slip events) are examined based on the analyses of repeating earthquakes and slow earthquakes with special focus on the interaction between different activities. A comprehensive analysis of the seismic and geodetic data from 2003 to 2016 indicates complementary distribution of various types of slow earthquakes down to 35–50 km depth outside the Nankai main locking area. We also found interactions between different kinds of activities. The interactions between the repeating earthquakes and slow earthquakes suggest that the area of the repeating earthquakes activity can be divided into deeper (depth ≥ 20 km) and shallower (depth < 20 km) areas. The analyses of deep repeating earthquakes and the inland Global Navigation Satellite System (GNSS) data suggests slow northward migrations of long-term slow slip events (SSEs) in 20–50 km (offshore Kyushu) and 20–35 km (under Shikoku) depths along the plate boundary. These migrations occurred during a period of 2–3 years that includes the 2003 and 2010 large slow-slip events in the Bungo channel located in between Kyushu and Shikoku. The analysis has also shown interaction between shallow repeating earthquakes and shallow very low frequency earthquakes which indicates faster northward migrations of short-term SSEs from the shallow plate boundary offshore Kyushu to the deeper area under Shikoku over the duration of a month during the 2010 long-term slow-slip episode. The deep slow migration and the shallow to deep fast migration of SSEs in a ∼300 km area towards and around the source area of the recurrent Nankai earthquake (Mw 8.0–8.6) indicates the occurrence of a widespread non-steady stress build-up process around the source area of the Nankai megathrust earthquake.