Records of the 5 March 2021 Raoul Island transoceanic tsunami around the Pacific Ocean

ABSTRACT

At 19:28 AM on 4 March 2021 (UTC), a M_w 8.1 megathrust earthquake occurred close to Raoul Island, New Zealand, on the Kermadec Subduction Zone. Closely following two other tsunamigenic ruptures, it triggered a tsunami that was quickly recorded by oceanic and coastal gauges. Analysis of 158 filtered sea-level records revealed that the tsunami had not only a regional impact but was recorded by most gauges in the Pacific Ocean and eight gauges in the Indian and the southern Atlantic Oceans, in good agreement with modelling results of tsunami propagation. Careful determination of tsunami arrival times and first and largest waves amplitude for each station support the fact that the first wave is almost never the highest one. The maximum amplitude is about three times higher than the first wave amplitude and the largest wave is recorded with a median value of ∼3 h after the first arrival. In addition, recordings of the largest wave of this small but transoceanic tsunami are not related to the distance to the earthquake epicentre. Finally, this tsunami which occurred simultaneously with several localised storms in the Pacific Ocean is an opportunity to highlight the difficulty in distinguishing between the different types of waves.

KEYWORDS:

• Transoceanic tsunami
• Megathrust earthquake
• Pacific Ocean
• Indian Ocean
• Atlantic Ocean
• Kermadec Subduction Zone
• De-tiding
• Filtering
• Signal analysis

Acknowledgments

The author would like to thank Dr Aditya Gusman (GNS Science) for TTT calculation included in Figure 2 and for his constructive comments, which help to improve the manuscript. The author is also very grateful to Dr Xiaoming Wang (GNS Science) who provided support for the use of COMCOT, and to the editor Dr Arishma Ram and two anonymous reviewers who provided constructive feedback to improve the quality of the article. Part of Figures 1 and 2 have been done with Generic Mapping Tools functions (Wessel et al. 2013) and the other Figures, including the filtering processes have been done with MATLAB® build-in functions.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Dataset available within the manuscript.

Additional information

Funding

This work was supported by GNS Science’s Hazards and Risk Management (HRM) science programme funded through the Strategic Science Investment Fund (SSIF).