10:00 AM - 10:15 AM
[SIT20-05] Stress loading on the 2021 M7.3 Fukushima-oki earthquake due to the 2011 M9 Tohoku-oki earthquake
Keywords:Stress change, 2021 Fukushima-oki Earthquake, 2011 Tohoku-oki Earthquake, Intra-slab earthquake, Pacific slab, Finite element method
On February 13, 2021, a Mj7.3 earthquake occurred off the coast of Fukushima (37.6°N, 141.5°E) at depth of 55 km, with a maximum seismic intensity of upper 6 in both Fukushima and Miyagi prefectures. This earthquake is a reverse-fault type with east-west compression, and is considered as an intra-slab earthquake within the subducting Pacific plate. In order to reveal the generation mechanism of this earthquake, it is important to know how the 2011 M9 Tohoku-oki earthquake affected this earthquake.
The crustal deformation during and after the 2011 Tohoku-oki earthquake has been observed by dense GPS observation network in the Japanese islands (GEONET). Freed et al. (2017) obtained the viscous structure under the Japanese islands and afterslip distribution based on the 3 years of postseismic deformation data since March 11, 2011. Based on this model, Becker et al. (2018) computed the time variation of the underground stress field. In this study, we calculate the stress change around the hypocenter of the 2021 Fukushima-oki earthquake, based on the postseismic deformation model by Freed et al. (2017) and Becker et al. (2018).
Setting the 0 stress before 2011, we plot the time variation of the displacement and stress field due to the Tohoku-oki earthquake in the cross section including the hypocenter of the Fukushima-oki earthquake. The displacement plot shows the continuous eastward movement after the Tohoku-oki. The average normal stress (σ11 + σ22 + σ33) / 3 shows that the hanging-wall side is widely extensional, while the footwall side including the hypocenter of the Fukushima-oki is compressive. Focusing on the hypocenter of the Fukushima-oki, the von Mises stress increases by about 1 MPa and the stress increase pattern is east-west compression. This stress change is consistent with the source mechanism of the Fukushima-oki earthquake, which suggests that the 2011 Tohoku-oki earthquake triggered this earthquake.
In order to estimate the stress change with more accuracy, it is necessary to obtain a stress change model that includes the effects of viscoelastic relaxation and afterslip based on 10-year crustal deformation data.
The crustal deformation during and after the 2011 Tohoku-oki earthquake has been observed by dense GPS observation network in the Japanese islands (GEONET). Freed et al. (2017) obtained the viscous structure under the Japanese islands and afterslip distribution based on the 3 years of postseismic deformation data since March 11, 2011. Based on this model, Becker et al. (2018) computed the time variation of the underground stress field. In this study, we calculate the stress change around the hypocenter of the 2021 Fukushima-oki earthquake, based on the postseismic deformation model by Freed et al. (2017) and Becker et al. (2018).
Setting the 0 stress before 2011, we plot the time variation of the displacement and stress field due to the Tohoku-oki earthquake in the cross section including the hypocenter of the Fukushima-oki earthquake. The displacement plot shows the continuous eastward movement after the Tohoku-oki. The average normal stress (σ11 + σ22 + σ33) / 3 shows that the hanging-wall side is widely extensional, while the footwall side including the hypocenter of the Fukushima-oki is compressive. Focusing on the hypocenter of the Fukushima-oki, the von Mises stress increases by about 1 MPa and the stress increase pattern is east-west compression. This stress change is consistent with the source mechanism of the Fukushima-oki earthquake, which suggests that the 2011 Tohoku-oki earthquake triggered this earthquake.
In order to estimate the stress change with more accuracy, it is necessary to obtain a stress change model that includes the effects of viscoelastic relaxation and afterslip based on 10-year crustal deformation data.