15:00 〜 15:15
[SCG61-30] Revisiting the Coseismic Slip Distribution of the 2011 Tohoku-oki Earthquake Considering Early Postseismic Deformation, Non-linear Viscoelasticity, and Heterogeneous Structure
キーワード：2011年東北地方太平洋沖地震、余効変動、非線形粘弾性
The 2011 Tohoku-oki earthquake produced large coseismic displacements that were detected by terrestrial and seafloor geodetic observations, namely, global navigation satellite systems (GNSS), GNSS-Acoustic (GNSS-A), and ocean bottom pressure (OBP) measurements. Previous studies constructed coseismic slip distribution models of the Tohoku-oki earthquake using the daily GNSS site coordinate time series, seafloor GNSS-A, and/or OBP data to estimate the coseismic displacements [e.g., Ito et al., 2011; Koketsu et al., 2011; Ozawa et al., 2011; Iinuma et al., 2012]. However, studies for these several years suggested that the coseismic displacements must include early postseismic deformation due to a low-viscosity zone beneath the Pacific plate that is necessary to explain terrestrial and seafloor postseismic crustal deformations [Sun et al., 2014; Freed et al., 2017; Suito, 2017]. This low-viscosity zone may not be persistent but could result in huge changes in stress resulting from the coseismic slip with reflecting non-linear rheology [Muto et al., 2018; Agata et al., 2019]. The effect of non-linear rheology is great immediately after a main shock. Therefore, coseismic displacements based on the daily site coordinate time series and GNSS-A measurements inevitably must include early postseismic deformation.
Thus, we derived “pure” coseismic displacements based on 1-Hz site coordinate time series at GNSS sites of the Geospatial Information Authority of Japan estimated by utilizing kinematic PPP (precise point positioning) analysis and based on 1-min average seafloor level time series at OBP sites. The residual displacements were obtained by subtracting the pure coseismic displacement from that based on the daily site coordinate time series. The data showed subsidence and trenchward motions in the entire Tohoku district. These broad deformations could not be explained solely by aftershocks nor by afterslip on the plate interface. Viscoelastic deformation that occurs immediately after the main shock is required to explain the displacement field. We present the results of our investigations into coseismic slip distribution and early postseismic deformation by applying Green’s function, which is calculated by considering the shapes of surface terrain and subducting slabs as well as heterogeneous thermal structures and power-law rheology.
References
Agata, R., et al. (2019). Rapid mantle flow with power-law creep explains deformation after the 2011 Tohoku mega-quake. Nat. Commun., in press.
Freed, A. M., et al. (2017). Resolving depth-dependent subduction zone viscosity and afterslip from postseismic displacements following the 2011 Tohoku-oki, Japan earthquake. Earth Planet. Sci. Lett., 459, 279-290, doi:10.1016/j.epsl.2016.11.040.
Iinuma, T., et al. (2012). Coseismic slip distribution of the 2011 off the Pacific Coast of Tohoku Earthquake (M9.0) refined by means of seafloor geodetic data. J. Geophys. Res., 117, B07409, doi:10.1029/2012JB009186.
Ito, T., et al. (2011). Slip distribution of the 2011 off the Pacific coast of Tohoku earthquake inferred from geodetic data, Earth Planets Space, 63, 627-630, doi:10.5047/eps.2011.06.023.
Koketsu, K., et al. (2011). A unified source model for the 2011 Tohoku earthquake. Earth Planet. Sci. Lett., 310, 480-487, doi:10.1016/j.epsl.2011.09.009.
Muto, J., et al. (2018). Nonlinear mechanical coupling between viscoelastic relaxation and deep afterslip in the post-seismic deformation of the 2011 Tohoku-oki earthquake. Abstract SCG57-30, presented at JpGU Meeting 2018, Chiba, Japan, 20-24 May.
Ozawa, S., et al. (2011). Coseismic and postseismic slip of the 2011 magnitude-9 Tohoku-Oki earthquake. Nature, 475, 373-376, doi:10.1038/nature10227.
Suito, H. (2017). Importance of rheological heterogeneity for interpreting viscoelastic relaxation caused by the 2011 Tohoku-Oki earthquake. Earth Planets Space, 69, 1, doi:10.1186/s40623-017-0611-9.
Sun, T., et al. (2014). Prevalence of viscoelastic relaxation after the 2011 Tohoku-oki earthquake. Nature, 514, 84-87, doi:10.1038/nature13778.
Thus, we derived “pure” coseismic displacements based on 1-Hz site coordinate time series at GNSS sites of the Geospatial Information Authority of Japan estimated by utilizing kinematic PPP (precise point positioning) analysis and based on 1-min average seafloor level time series at OBP sites. The residual displacements were obtained by subtracting the pure coseismic displacement from that based on the daily site coordinate time series. The data showed subsidence and trenchward motions in the entire Tohoku district. These broad deformations could not be explained solely by aftershocks nor by afterslip on the plate interface. Viscoelastic deformation that occurs immediately after the main shock is required to explain the displacement field. We present the results of our investigations into coseismic slip distribution and early postseismic deformation by applying Green’s function, which is calculated by considering the shapes of surface terrain and subducting slabs as well as heterogeneous thermal structures and power-law rheology.
References
Agata, R., et al. (2019). Rapid mantle flow with power-law creep explains deformation after the 2011 Tohoku mega-quake. Nat. Commun., in press.
Freed, A. M., et al. (2017). Resolving depth-dependent subduction zone viscosity and afterslip from postseismic displacements following the 2011 Tohoku-oki, Japan earthquake. Earth Planet. Sci. Lett., 459, 279-290, doi:10.1016/j.epsl.2016.11.040.
Iinuma, T., et al. (2012). Coseismic slip distribution of the 2011 off the Pacific Coast of Tohoku Earthquake (M9.0) refined by means of seafloor geodetic data. J. Geophys. Res., 117, B07409, doi:10.1029/2012JB009186.
Ito, T., et al. (2011). Slip distribution of the 2011 off the Pacific coast of Tohoku earthquake inferred from geodetic data, Earth Planets Space, 63, 627-630, doi:10.5047/eps.2011.06.023.
Koketsu, K., et al. (2011). A unified source model for the 2011 Tohoku earthquake. Earth Planet. Sci. Lett., 310, 480-487, doi:10.1016/j.epsl.2011.09.009.
Muto, J., et al. (2018). Nonlinear mechanical coupling between viscoelastic relaxation and deep afterslip in the post-seismic deformation of the 2011 Tohoku-oki earthquake. Abstract SCG57-30, presented at JpGU Meeting 2018, Chiba, Japan, 20-24 May.
Ozawa, S., et al. (2011). Coseismic and postseismic slip of the 2011 magnitude-9 Tohoku-Oki earthquake. Nature, 475, 373-376, doi:10.1038/nature10227.
Suito, H. (2017). Importance of rheological heterogeneity for interpreting viscoelastic relaxation caused by the 2011 Tohoku-Oki earthquake. Earth Planets Space, 69, 1, doi:10.1186/s40623-017-0611-9.
Sun, T., et al. (2014). Prevalence of viscoelastic relaxation after the 2011 Tohoku-oki earthquake. Nature, 514, 84-87, doi:10.1038/nature13778.