10:45 AM - 11:00 AM
[SSS04-06] Numerical modeling of the significant tsunami later phase associated with the 2022 Tonga volcanic eruption
★Invited Papers
Keywords:Tsunami, The 2022 Tonga volcanic eruption, Ocean-bottom pressure gauge
The 2022 eruption of the Hunga Tonga-Hunga Ha’apai volcano triggered the singular tsunamis observed globally. While the first arrival is now widely known to be related to the atmospheric Lamb wave generated by the eruption (e.g., Kubota et al., 2022), additional significant later phases whose amplitudes were comparable to the first ones were also recorded around Japan (e.g., Kubo et al., 2022).
In this study, we estimated the source of the later phases based on the Vespa analysis (e.g., Rost and Thomas, 2002) and proposed a new numerical scheme to reproduce them.
The Vespa analysis estimates the arrival time and incident angle of each signal by a slant-stack process using its theoretical travel time. We applied it to the records of ocean-bottom pressure gauges of DONET and S-net, and the ones of barometers of SORATENA. The Vespa analysis revealed that small atmospheric waves, different from the first arrival, excited the large later tsunamis.
For numerical simulations, we used two types of synthetic methods: finite difference method and normal mode theory (Harkrider and Press, 1967). While the finite difference method can consider the bathymetric effect, the model of the atmosphere must be assumed to be isotropic due to its high computational cost. On the other hand, the normal mode theory uses a realistic 1D atmosphere model but flat bathymetry is required. Through these numerical experiments, we found that both a good atmospheric wave model and bathymetric effect were important to excite the atmospheric-induced tsunamis corresponding to the later phases.
We therefore proposed a new hybrid calculation method: calculating tsunamis by the finite difference method with the atmospheric waves by the normal mode theory as the input. This hybrid method successfully reproduced the observed records, particularly in amplitude over the entire records.
In this study, we estimated the source of the later phases based on the Vespa analysis (e.g., Rost and Thomas, 2002) and proposed a new numerical scheme to reproduce them.
The Vespa analysis estimates the arrival time and incident angle of each signal by a slant-stack process using its theoretical travel time. We applied it to the records of ocean-bottom pressure gauges of DONET and S-net, and the ones of barometers of SORATENA. The Vespa analysis revealed that small atmospheric waves, different from the first arrival, excited the large later tsunamis.
For numerical simulations, we used two types of synthetic methods: finite difference method and normal mode theory (Harkrider and Press, 1967). While the finite difference method can consider the bathymetric effect, the model of the atmosphere must be assumed to be isotropic due to its high computational cost. On the other hand, the normal mode theory uses a realistic 1D atmosphere model but flat bathymetry is required. Through these numerical experiments, we found that both a good atmospheric wave model and bathymetric effect were important to excite the atmospheric-induced tsunamis corresponding to the later phases.
We therefore proposed a new hybrid calculation method: calculating tsunamis by the finite difference method with the atmospheric waves by the normal mode theory as the input. This hybrid method successfully reproduced the observed records, particularly in amplitude over the entire records.