2006 Tonga earthquake

Earthquake in Tonga

The 2006 Tonga earthquake occurred on 4 May at with a moment magnitude of 8.0 and a maximum Mercalli intensity of VII (very strong). One injury occurred and a non destructive tsunami was observed.

The National Oceanic and Atmospheric Administration's Pacific Tsunami Warning Center in Hawaii issued a warning 17 minutes after the earthquake for coastal areas around the Pacific. An hour later, the center downgraded the warning to only the region within 600 miles of the epicenter, and an hour after that, it canceled the alert. The earthquake was followed by a pair of large aftershocks the next day.

The event caused very limited damage. The previous large earthquake in Tonga, in 1977, was of a lower magnitude but resulted in more severe damage. A likely cause is that the 2006 quake generated other frequencies that only resulted in resonance in small items. In shops, cans and bottles fell from shelves. A Korean business man jumped in panic from his second floor hotel room and was hurt in the fall. He was brought to the hospital where he had to wait a long time for any help as power was off and most staff off duty (as that day was a public holiday). The American wharf in Nukualofa sustained cracks in addition to those caused by the 1977 earthquake. A ship, sunk in 1949 near Toula, Vavau apparently burst open and its load of copra came floating to the ocean surface. A landslide occurred at Hunga island in Vavau, when the ground at a steep cliff along the shore began sliding into the sea. In Haapai, the islands closest to the epicentre, the wharf was damaged and a number of water pipes and telephone lines were broken. Niuui hospital was damaged.

Since the earthquake occurred underwater, tsunami warnings were issued, but then lifted. A small tsunami was observed. Later analysis showed the earthquake to be a slab tearing event and so less conducive to tsunami generation.