Estimating the Nankai Trough Megathrust Earthquake’s Anticipated Fiscal Impact on Japanese Governments

This study estimates the fiscal impact of the anticipated Nankai Trough Megathrust Earthquake on both the national and local Japanese governments to identify their sovereign risk. First, we estimate the impact of the Great East Japan Earthquake on local public finance using panel data regressions on 2008–2015 fiscal data. Second, based on the anticipated damage data – seismic intensity and area of inundation – of the Nankai earthquake and the coefficients derived from the first step, we estimate the amounts of fiscal revenue and expenditures that would be required by every local government for the anticipated Nankai earthquake. Finally, we estimate the fiscal expenditure of the national government in proportion to the estimated local ones. We find that first, the estimated fiscal requirements in the two years after the earthquake are about JPY 161 trillion, 5.9 times those of the 2011 Great East Japan Earthquake. Second, the financial disparity between affected and non-affected local governments is large because the Nankai earthquake would affect more municipalities than the Great East Japan Earthquake. The fiscal burden of non-affected municipalities would be relatively higher. These findings indicate that the Nankai earthquake will not only be a local disaster but also a national catastrophe.

Internal structure, active tectonics and dynamic topography of the eastern Nankai accretionary prism toe, Japan, and its tsunamigenic potential

The eastern Nankai accretionary prism toe was surveyed to evaluate the nature and deformation of its frontal thrust. According to the determined porosities and yield strengths, turbidites were successively buried down to depths of 250–300 m before accretion, and were then exposed at the prism toe by uplift along the Tenryu frontal thrust during 3.4–1.98 Ma. Consolidation tests provided reasonable estimates of burial depth and, when combined with exposed sediment dates, yield prism toe uplift rates of 0.74–2.27 m ka–1. The displacement along the frontal thrust is estimated to be 500–900 m and the slip rates are 1.47–4.55 m ka–1, corresponding to the highest class of active faults on land in Japan. During the surveys of the Tenryu frontal thrust zone, we discovered a new active fault scarp that was several tens of centimetres high, interpreted to be a protothrust located c. 100 m south of the frontal thrust. This scarp is associated with chemosynthetic biocommunities. The thrust might potentially be the result of displacement during the East Nankai (To-Nankai) earthquake (Mw 8.1) in 1944. These lines of evidence indicate that the Tenryu frontal thrust is still active and that displacement along the thrust might induce a tsunami during future Tokai or To-Nankai earthquakes.

Preliminary Study on Long-Term Flooding After the Tsunami

After the Nankai earthquake in 1946, the resultant flooding lasted for a long time, because seawater remained on land after the tsunami in Kochi city. Large-scale flooding occurred in Ishinomaki city immediately after the Great East Japan Earthquake in 2011. Long-term flooding may hamper disaster responses such as rescue and recovery activities. This paper studied the risks of long-term flooding after the Nankai earthquake in Tokushima city based on a paleographical survey and numerical analysis. The paleographical survey identified statements such as “seawater sometimes flowed onto the land at the full tide,” suggesting occurrences of long-term flooding after previous Nankai earthquakes. The numerical analysis separately calculated values inside and outside the levee. The tsunami waveforms outside the analysis area obtained by tsunami numerical simulation was used as the boundary condition of the inland flow modeling, that is water was introduced inside the levee when the tsunami water level exceeded the upper end of the levee. The two layers of ground surface and the drain were defined to calculate the flow, including water exchange between the two layers, and the water was drained forcefully outside the levee using a drainage pump. The possibility of long-term flooding in the analysis area is suggested when a large-scale earthquake occurs in the Nankai trough.

Earthquake and Tsunami Scenarios as Basic Information to Prepare Next Nankai Megathrust Earthquakes

This paper describes earthquake and tsunami scenarios as basic information for preparing for the next Nankai megathrust earthquakes. Models to clarify the size of the Nankai megathrust earthquake and changes in occurrence intervals, simulations using such models, and simulations of crustal deformations and tsunamis based on the simulations were employed. This paper re-examines past earthquakes and tsunamis, the possibility of slightly larger earthquakes and tsunamis, their sizes, the necessity of countermeasures against subsidence caused by earthquakes in the Inland Sea, the possibility of the Nankai earthquake occurrence before the Tokai (Tonankai) earthquake, and the possibility of the triggering of the Nankai earthquake by the Hyuga-nada earthquake.