The 2021 South Sandwich Islands tsunami: from the Antarctic to the far Northeast corner of the Pacific Ocean

Abstract The major earthquake sequence that struck near the South Sandwich Islands in the Antarctic sector of the Atlantic Ocean on August 12, 2021, began with a magnitude M w 7.5 rupture at 18:33 UTC, followed by a more intense M w 8.1–8.3 mainshock three minutes later. The tsunami generated by this complex event spread throughout the World Ocean, where, in the northeast Pacific Ocean, it was observed in such distal regions as California, British Columbia and the Aleutian Islands, 15,000–18,000 km from the source area. Tsunami waves recorded by multiple oceanic sensors show that the tsunami arrived at the coast of Vancouver Island about 23 h after the earthquake and then two hours later at coastal Alaska and the Aleutian Islands. The 10–20 min period waves that dominated both the coastal and open-ocean tsunami waveforms appear to be tightly associated with the source properties. A numerical model developed for the event closely reproduces the open-ocean records. To achieve this close agreement between the observed and modelled tsunami waveforms in deep water, we adjusted the model to account for the dispersion that occurred during propagation of the waves across the Pacific Ocean. Our findings further show that kinematic models commonly used for tsunami warnings (and based solely on “dead-reckoning” estimates of wave front trajectories) give for far-field events earlier estimated arrival times (ETAs) than the measurable arrival times (TAs) of the tsunami waves.