17:15 〜 18:45
[SCG53-P06] Feasibility study of wave gradiometry for real-time monitoring of tsunamis
キーワード：津波、リアルタイムモニタリング、アレイ解析
Earthquake and tsunami early warnings are essential to mitigate disasters from these events. The initial warnings should be issued from analyses of limited data; hence, revisions of the warnings are necessary as the details of each event are revealed. Seismic or tsunami wavefields should reflect complex source and propagation properties from the initiation to the current time so that monitoring the current wavefield may be useful to update the early warnings.
Array analysis is a powerful tool to reveal the propagation properties of the waves. Thanks to the recent deployment of dense geophysical networks, array analysis can be applicable without temporal observations. It is also possible to conduct array analyses in real-time so that the analyses may contribute to monitoring the wavefield. In this study, we investigate the applicability of the array analyses of the ocean bottom pressure gauges (OBPGs) for monitoring the tsunami wavefield.
On 2 December 2023, a magnitude 7.6 earthquake occurred near Hinatuan, Philippines, and the event excited the tsunami. The Dense Oceanfloor Network system for Earthquakes and Tsunami (DONET) OBPG array deployed off the Kii Peninsula observed the tsunami, so we conducted the array analysis with the OBPG array. We used the wave gradiometry method to calculate not only the slowness vectors of the waves but also the information about amplitude decay. The method also has the advantage of requiring less computational cost than conventional array analyses such as the semblance method. Applying the wave gradiometry to the pressure records of the DONET array, we successfully visualized tsunami propagation from the south (i.e., epicenter) to the north among the array. Estimated propagation velocities are consistent with those calculated from linear long-wave theory. This result implies that the tsunami arrivals may be forecasted by the extrapolation of observations at OBPGs using ray theory. In contrast, the apparent geometrical spreading, which is the output of the wave gradiometry, shows amplitude decay during the tsunami propagation among OBPGs. This feature is inconsistent with the Green’s law which describes the relationship between tsunami amplitudes and the sea water depth. Amplitude attenuation during propagation is an interesting issue in tsunami science but it raises an issue of how we utilize the amplitude information from the wave gradiometry to tsunami early warnings. We will further investigate the propagation properties of the tsunami excited by the 2 December earthquake with synthesized tsunami waves.
Acknowledgment
We thank the National Research Institute for Earth Science and Disaster Resilience for providing the pressure waveforms recorded by the DONET OBPGs.
Array analysis is a powerful tool to reveal the propagation properties of the waves. Thanks to the recent deployment of dense geophysical networks, array analysis can be applicable without temporal observations. It is also possible to conduct array analyses in real-time so that the analyses may contribute to monitoring the wavefield. In this study, we investigate the applicability of the array analyses of the ocean bottom pressure gauges (OBPGs) for monitoring the tsunami wavefield.
On 2 December 2023, a magnitude 7.6 earthquake occurred near Hinatuan, Philippines, and the event excited the tsunami. The Dense Oceanfloor Network system for Earthquakes and Tsunami (DONET) OBPG array deployed off the Kii Peninsula observed the tsunami, so we conducted the array analysis with the OBPG array. We used the wave gradiometry method to calculate not only the slowness vectors of the waves but also the information about amplitude decay. The method also has the advantage of requiring less computational cost than conventional array analyses such as the semblance method. Applying the wave gradiometry to the pressure records of the DONET array, we successfully visualized tsunami propagation from the south (i.e., epicenter) to the north among the array. Estimated propagation velocities are consistent with those calculated from linear long-wave theory. This result implies that the tsunami arrivals may be forecasted by the extrapolation of observations at OBPGs using ray theory. In contrast, the apparent geometrical spreading, which is the output of the wave gradiometry, shows amplitude decay during the tsunami propagation among OBPGs. This feature is inconsistent with the Green’s law which describes the relationship between tsunami amplitudes and the sea water depth. Amplitude attenuation during propagation is an interesting issue in tsunami science but it raises an issue of how we utilize the amplitude information from the wave gradiometry to tsunami early warnings. We will further investigate the propagation properties of the tsunami excited by the 2 December earthquake with synthesized tsunami waves.
Acknowledgment
We thank the National Research Institute for Earth Science and Disaster Resilience for providing the pressure waveforms recorded by the DONET OBPGs.