CASE STUDIES OF TSUNAMI CONSIDERING WITH TIME LAG OF FAULTS RUPTURE IN EASTERN JAPAN SEA

Abstract

The 2011 tohoku earthquake tsunami inflicted catastrophe on Tohoku region in Japan. Magnitude of the tsunami exceeded design conditions of tsunami breakwater, seawalls and so on. A difficulty of fixing a design tsunami was re-recognized from the view point of disaster prevention. Of course, since total faults rupture scale was huge, the tsunami became so large that we were not able to anticipate in advance. Seismic researchers, that analyzed the 2011 tohoku earthquake, are pointing out that several faults slid with time lag. The faults rupture time lag should be also considered as one of the reason why the tsunami became large. However, even if the parameters of faults rupture could be set in terms of a disaster prevention design, it is so hard to determine faults rupture time lag. Therefore, this paper investigated influence of faults rupture time lag on tsunami height by numerical simulation. Case studies were carried out to evaluate tsunami that was generated two faults with time lag. Two simulation methods were applied. One of them is that tsunami generated by two faults with time lag calculated simultaneously (simultaneous simulation). Another one is a method based on the superposition. Simulation of tsunami caused by each fault is conducted independently. The tsunami profiles from two simulations are added considering with the time lag of faults rupture. This is positioned as a convenient method in order to reduce computational cost. Case studies were performed in Japan Sea and both simulation results were compared at 33 locations. As the results, faults rupture time lag affected tsunami height. And the time lag, makes to occur maximum tsunami height, was different at each location. Finally, it was confirmed that the convenient method based on the superposition could give almost same result as simultaneous simulation.