Tsunami Induced Oscillations: Along the South Shore of O‘ahu Hawai‘i

Abstract

The State of Hawai‘i has put a great deal of effort into implementing tsunami safety and preparedness measures. Despite these efforts, strong currents caused by tsunami induced oscillations may pose significant hazards to Hawai‘i residents who are uninformed of their presence. Pressure measurements collected by Pacific Islands Ocean Observing System (PacIOOS) nearshore sensors during the 2010 Maule, 2011 Tohoku, and 2022 Tonga tsunamis show that tsunami oscillations produced water level variations which gradually decreased over time. These oscillations were estimated to last from 20.70 ± 0.08 hours to 37.80 ± 0.24 hours at specific sensor sites. The average duration time across all datasets was 30.00 ± 0.12 hours. Additionally, the variations induced by these tsunami events exhibited periodic behavior, with the largest oscillations occurring near a 42.0-minute period. The median peak value was determined to be 42.1 minutes and the range of peak values was determined to be 0.4 minutes. This study hypothesizes that tsunami induced oscillations along the south shore of O‘ahu, Hawai‘i are the result of resonance behavior between the tsunami and the surrounding bathymetry, and that the 42.1-minute period is the dominant resonance frequency along the south shore of O‘ahu. These results may be useful for forecasting tsunami oscillations along the south shore of O‘ahu because they indicate a driving mechanism with predictable behavior. This information can be used by the State of Hawai‘i to determine when it is safe for residents and visitors to go back into the water after one of these events.