[SSS13-09] Seismic activity of the off-Yamagata Earthquake in 2019 and crustic movement of the NorthEast Honshu Arc
Keywords:Off-Yamagata earthquake in 2019, seismic activity, crustic mvement, crustic slide, uplift of arc
A large earthquake 6.7 Mj(according to JMA), called the Yamagata-ken Oki jishin (Yamagata Offshore Earthquake), occurred on 18th June 2019 at 22:22 JST, offshore of Yamagata Prefecture, northwest Japan. There is few human damage luckily, but damage of less than 800 houses occurred near the epicenter around the border of Yamagata and Niigata Prefectures.
Maximum seismic intensity is 6 upper in northern margin of Murakami City, Niigata Prefecture and the second largest seismic intensity if 6 lower in southern margin of Tsuruoka City, Yamagata Prefecture. According to JMA Estimated seismic intensity map. Seismic intensity decreases as moving farther away from the epicenter.
Focal mechanism of Yamagata Offshore Earhquake in 2019 is derived by JMA (2019) as that strike of both nodal planes is NNE-SSW,and one of the nordal plane dips westward steeply and the other dips eastward gently. According to the distribution of aftershocks, the fault plae causing the earthquake corresponds to the nordal plane dipping eastward gently. This indicates that the landward hanging wall run onto the seaward footwall.
There are two mountain ranges along the arc in the Northeast Japan Arc; namely Ou Mountains on the axis of the arc and Dewa Hills along the Japan Sea. and there are seven muntain ranges running orthogonally to the ranges along the arc. Basment rocks as granitic rocks and active vlcanoes often appears on the ranges of both direcitons. These geological features indicate that the ranges of both directrions are actively uplifting and the movemtnt of the ranges are drived by the magmatic acrivity in the clust or the upper mantle. Magmatic activity under the ranges are also provided by the seismic tomography (Hasegawa and Nakajima, 2009).
The Yamagata Ofshore Earthquake in 2019 occurred on the anterior position of the orthognal mountain ranges. This means that the fault movement causing the earthquake is drived by sagging seaward of the end of uplifting mountain ranges.
References:
HASEGAWA Akira and NAKAJIMA Junichi (2009) Deep Stucture of the NE Japan arc and lts Implications for Tectenic Movement. Earth Sciene (Chikyu Kagaku),63,201-210.
JMA (2019) Monthly report of earthquake and volcanoes in Japan, June 2019.
Maximum seismic intensity is 6 upper in northern margin of Murakami City, Niigata Prefecture and the second largest seismic intensity if 6 lower in southern margin of Tsuruoka City, Yamagata Prefecture. According to JMA Estimated seismic intensity map. Seismic intensity decreases as moving farther away from the epicenter.
Focal mechanism of Yamagata Offshore Earhquake in 2019 is derived by JMA (2019) as that strike of both nodal planes is NNE-SSW,and one of the nordal plane dips westward steeply and the other dips eastward gently. According to the distribution of aftershocks, the fault plae causing the earthquake corresponds to the nordal plane dipping eastward gently. This indicates that the landward hanging wall run onto the seaward footwall.
There are two mountain ranges along the arc in the Northeast Japan Arc; namely Ou Mountains on the axis of the arc and Dewa Hills along the Japan Sea. and there are seven muntain ranges running orthogonally to the ranges along the arc. Basment rocks as granitic rocks and active vlcanoes often appears on the ranges of both direcitons. These geological features indicate that the ranges of both directrions are actively uplifting and the movemtnt of the ranges are drived by the magmatic acrivity in the clust or the upper mantle. Magmatic activity under the ranges are also provided by the seismic tomography (Hasegawa and Nakajima, 2009).
The Yamagata Ofshore Earthquake in 2019 occurred on the anterior position of the orthognal mountain ranges. This means that the fault movement causing the earthquake is drived by sagging seaward of the end of uplifting mountain ranges.
References:
HASEGAWA Akira and NAKAJIMA Junichi (2009) Deep Stucture of the NE Japan arc and lts Implications for Tectenic Movement. Earth Sciene (Chikyu Kagaku),63,201-210.
JMA (2019) Monthly report of earthquake and volcanoes in Japan, June 2019.