11:00 AM - 1:00 PM
[MIS13-P03] Tsunami source estimation based on high-density tsunami deposit data and sediment transport numerical analysis
Keywords:2011 Tohoku-oki tsunami, Paleotsunami, Numerical modeling, Tsunami source modeling
Quantification of paleotsunami source characteristics is one of the key issues of paleotsunami research, and numerous attempts have been made to estimate the paleotsunami source. Numerical modeling of tsunami sediment transport is a powerful tool for the quantification of tsunami sources. However, because the tsunami sediment transport modeling became available only recently, the capability and limitation of source estimation with sediment transport simulation have not yet been investigated. In this study, to clarify how much information about the tsunami source characteristics can be extracted from tsunami deposits, we performed a source estimation of the 2011 Tohoku-oki tsunami (TOT) based on tsunami sediment transport numerical modeling combined with sedimentary data of the tsunami deposits.
The thickness of the tsunami deposits was measured extensively in the southern edge of the Sendai Plain, Miyagi Prefecture (Abe et al., 2020). The volume of the tsunami deposits was calculated based on the dense thickness data and was used as a boundary condition of the numerical modeling. The TUNAMI-STM code (Sugawara et al., 2014; Yamashita et al., 2016) was employed to simulate tsunami propagation, inundation, and sediment transport. Coseismic crustal deformation due to the activity of interplate fault along the Japan Trench was assumed to be the tsunami source. The fault was divided into 10 rectangular subfaults with dimensions of L = 100 km × W = 100 km based on Hayashi and Koshimura (2012).
Coseismic fault slips on only two segments located off Fukushima were investigated because sensitivity analysis showed that slips on the other subfaults were inferred to have minor effects on sediment transport in the study area. As a result of the trial-and-error approach constrained by the tsunami deposit volume, a fault slip of over 35 m was estimated near the trench axis. Fault slip on the deeper part of the plate boundary was not well constrained only by the deposit volume of the study area. Nevertheless, a fault slip of 10 m was estimated on the deeper subfault, considering the simulated distribution of nearshore erosion and sediment source inferred from geological data.
Area of possible slip recovery based on the tsunami deposits data from the southern Sendai Plain is limited to the fault segments located off Fukushima. This suggests that it is difficult to reconstruct the characteristics of the entire tsunami source as long as it is based only on data from a single, small area. In this study, the fault slip estimated by the deposit data is larger than that by previous studies. This difference may be associated with contributions from segments other than the Fukushima offshore area. This implies that the accuracy of the slip estimation can be improved if regional high-quality tsunami deposit data is available.
The thickness of the tsunami deposits was measured extensively in the southern edge of the Sendai Plain, Miyagi Prefecture (Abe et al., 2020). The volume of the tsunami deposits was calculated based on the dense thickness data and was used as a boundary condition of the numerical modeling. The TUNAMI-STM code (Sugawara et al., 2014; Yamashita et al., 2016) was employed to simulate tsunami propagation, inundation, and sediment transport. Coseismic crustal deformation due to the activity of interplate fault along the Japan Trench was assumed to be the tsunami source. The fault was divided into 10 rectangular subfaults with dimensions of L = 100 km × W = 100 km based on Hayashi and Koshimura (2012).
Coseismic fault slips on only two segments located off Fukushima were investigated because sensitivity analysis showed that slips on the other subfaults were inferred to have minor effects on sediment transport in the study area. As a result of the trial-and-error approach constrained by the tsunami deposit volume, a fault slip of over 35 m was estimated near the trench axis. Fault slip on the deeper part of the plate boundary was not well constrained only by the deposit volume of the study area. Nevertheless, a fault slip of 10 m was estimated on the deeper subfault, considering the simulated distribution of nearshore erosion and sediment source inferred from geological data.
Area of possible slip recovery based on the tsunami deposits data from the southern Sendai Plain is limited to the fault segments located off Fukushima. This suggests that it is difficult to reconstruct the characteristics of the entire tsunami source as long as it is based only on data from a single, small area. In this study, the fault slip estimated by the deposit data is larger than that by previous studies. This difference may be associated with contributions from segments other than the Fukushima offshore area. This implies that the accuracy of the slip estimation can be improved if regional high-quality tsunami deposit data is available.