11:45 AM - 12:00 PM
[S08-2-05] A large slip area of the 2011 Tohoku-oki earthquake has been already ruptured by the 1611 Keicho Tsunami earthquake (Mw9.0)
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The 1611 Keicho Tsunami earthquake generated huge tsunamis and caused a disaster along the Pacific coast of Tohoku area from Fukushima to Miyako. There are several historical documents, but some of them were controversial. Recently, Ebina and Imai (2012) checked historical documents in detail and made the most reliable data set of the tsunami inundation of the 1611 Keicho Tsunami. We compared the data set with the tsunami inundation of the 2011 Tohoku tsunami and found that the tsunami from the 1611 tsunami earthquake inundated larger distance than the 2011 Tohoku tsunami at many places.
The numerical tsunami inundation computations were carried out along the Pacific coast of Tohoku where reliable tsunami evidences of historical documents were available, such as tsunami evidence about 30 m height at Koyadori in Iwate or tsunami evidence at Suwa in the Sendai plain about 7 km away from the coast. Result indicates that the tsunami generated from the combination of two rectangular fault models, north fault with the length of 100 km, the width of 100 km, and the slip amount of 80 m and south fault with the length of 150km, the width of 100 km, and the slip amount of 40 m, explains all reliable evidences very well. The moment magnitude of the 1611 tsunami earthquake is calculated to be 9.0 by assuming that the rigidity is 3 x 10**11 N/m**2.
The northern part of the fault is located the north of the large slip area of the 2011 Tohoku-oki earthquake. The southern part of the fault, where 40 m slip was estimated, is located at the almost same area of the large slip area of the 2011 Tohoku-oki earthquake. This suggested that the 2011 Tohoku-oki earthquake re-ruptured the southern part of fault area ruptured by the 1611 Keicho tsunami earthquake. Because the plate convergence rate of Pacific plate along the Japan Trench is about 9 cm/year. A large slip of about 45 m estimated for the 2011 Tohoku-oki earthquake is similar to 36 m estimated from the convergence rate.
The numerical tsunami inundation computations were carried out along the Pacific coast of Tohoku where reliable tsunami evidences of historical documents were available, such as tsunami evidence about 30 m height at Koyadori in Iwate or tsunami evidence at Suwa in the Sendai plain about 7 km away from the coast. Result indicates that the tsunami generated from the combination of two rectangular fault models, north fault with the length of 100 km, the width of 100 km, and the slip amount of 80 m and south fault with the length of 150km, the width of 100 km, and the slip amount of 40 m, explains all reliable evidences very well. The moment magnitude of the 1611 tsunami earthquake is calculated to be 9.0 by assuming that the rigidity is 3 x 10**11 N/m**2.
The northern part of the fault is located the north of the large slip area of the 2011 Tohoku-oki earthquake. The southern part of the fault, where 40 m slip was estimated, is located at the almost same area of the large slip area of the 2011 Tohoku-oki earthquake. This suggested that the 2011 Tohoku-oki earthquake re-ruptured the southern part of fault area ruptured by the 1611 Keicho tsunami earthquake. Because the plate convergence rate of Pacific plate along the Japan Trench is about 9 cm/year. A large slip of about 45 m estimated for the 2011 Tohoku-oki earthquake is similar to 36 m estimated from the convergence rate.