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[J04-P-07] Decay Properties of Bay Oscillations Induced by the Tsunami of Nankai-Trough Earthquake
In order to better understand the duration of tsunamis caused by large earthquakes, we investigate resonance responses of bays and their decay properties based on tsunami simulations for the Nankai-trough earthquake.
It has been reported that tsunami-induced oscillations in bays continue for a very long time, up to several tens of hours. For example, the tsunami warning of the 2011 Tohoku-Oki earthquake (Mw9.0) could not be canceled for two days after the earthquake. A good estimation of when tsunamis are settled is required for operations such as rescue, marine traffic, and coastal factories.
In this study, we examined the tsunami durations in bays based on the simulations for the eleven Nankai-trough earthquake source models provided by the Central Disaster Prevention Council (CDPC) of Japan. We focused on the tsunami properties in bays around the Tokyo bay, i.e., the Tokyo, Sagami and Suruga bays. The result of spectral analysis of the simulated waveforms confirmed that these bays have the same peak periodic component of period of 〜70 min for the four of the eleven CDPC sources and T = 〜80 min for the other seven sources. For all the eleven sources, a large component of T = 〜110 min appears only in the Tokyo bay, implying that the component is the result of the resonance oscillation of the Tokyo bay.
We then investigated the decay time constant of each periodic component to understand the duration of the tsunamis that last in the bays. When the peak spectral period of T = 〜70 min is generated in Tokyo bay, the average decay time constant is 〜600 min for both components of T = 〜70 and 〜110 min. On the other hand, when the peak spectral period of T = 〜80 min appears, the component of T = 〜110 min has a longer decay time constant of 〜800 min and that of the component of T = 〜80 min is 〜600 min. These results suggest that the decay property of each spectral component is not independent but interacts with each other.
It has been reported that tsunami-induced oscillations in bays continue for a very long time, up to several tens of hours. For example, the tsunami warning of the 2011 Tohoku-Oki earthquake (Mw9.0) could not be canceled for two days after the earthquake. A good estimation of when tsunamis are settled is required for operations such as rescue, marine traffic, and coastal factories.
In this study, we examined the tsunami durations in bays based on the simulations for the eleven Nankai-trough earthquake source models provided by the Central Disaster Prevention Council (CDPC) of Japan. We focused on the tsunami properties in bays around the Tokyo bay, i.e., the Tokyo, Sagami and Suruga bays. The result of spectral analysis of the simulated waveforms confirmed that these bays have the same peak periodic component of period of 〜70 min for the four of the eleven CDPC sources and T = 〜80 min for the other seven sources. For all the eleven sources, a large component of T = 〜110 min appears only in the Tokyo bay, implying that the component is the result of the resonance oscillation of the Tokyo bay.
We then investigated the decay time constant of each periodic component to understand the duration of the tsunamis that last in the bays. When the peak spectral period of T = 〜70 min is generated in Tokyo bay, the average decay time constant is 〜600 min for both components of T = 〜70 and 〜110 min. On the other hand, when the peak spectral period of T = 〜80 min appears, the component of T = 〜110 min has a longer decay time constant of 〜800 min and that of the component of T = 〜80 min is 〜600 min. These results suggest that the decay property of each spectral component is not independent but interacts with each other.