PTWS Post-event Debrief and Hotwash - 4 March 2021, M8.1, Kermadec Islands Region Earthquake and Tsunami

Résumé

The debrief and hotwash will focus on the PTWS’s international and national tsunami warning and emergency response to this event. The PTWC, Pacific Island Countries and Territories, South America, and Central America will share their responses. This will be followed by an open discussion aimed at answering country questions, and identifying priority recommendations needed to improve the PTWS and national responses. GoToWebinar registration: https://attendee.gotowebinar.com/register/3586211519192875276 Event Summary At 1928Z, a M8.1 shallow thrust-fault earthquake in the Tonga-Kermadec Trench generated a tsunami that was observed locally and across the Pacific Basin. The earthquake followed nearby M7.4 foreshock that occurred ~107 minutes earlier and a M7.3 ~900 km to the south six hours earlier. The PTWC issued a Tsunami Threat Message at 1937Z based on the earthquake's magnitude, its first RIFT forecast at 1958Z, and its Final Tsunami Threat Message at 1222Z on 5 March (22 messages over 17 hours). In nearby Pacific Island Countries, warning or advisories were issued soon after, with some evacuations taking place, followed by cancellations after either no or only small waves were observed. In the eastern Pacific, the Galapagos, and parts of Central and South America had forecasts of 0.3-1m. Maximum observed amplitudes reported by PTWC were 0.56 m at Norfolk Island west of the epicenter and 0.48 m in the Galapagos, Ecuador to the east northeast. On Raoul Island, the largest of the Kermadec Islands and near to the epicenter, data communication were knocked out by the earthquake, including for the sea level gauges that would have been used to confirm the severity of any tsunami from the M8.1 earthquake. The event was recorded on nearby NZ and US DART systems, and used by the NZ GNS and PTWS to validate forecasts during the event. Post-event reconnaissance revealed at least 0.79g of ground acceleration was measured and numerous landslides.