Firstly, it is good to hear no reports of injury or damage in Tonga following their early morning earthquake. These types of events are always unnerving, especially when they happen during the middle of the night when people may be particularly tired and less able to process the many emotions an earthquake can create, so it is encouraging to hear that many people did evacuate appropriately in case of tsunami.

"This event is a little different than the 2022 Hunga Tonga-Hunga Ha’apai eruption which had the challenge of a conflict between evacuating from the tsunami and staying inside to avoid ashfall, but it may still bring back difficult memories for those who experienced the eruption. Hopefully appropriate psychological support is provided to those who need it. It is important to remember that earthquake impacts can look like much more than just damaged buildings or physical injury.

"New Zealanders may be a bit worried about the earthquakes we’ve been feeling here and seeing overseas, including last week's earthquake off Southland, and the ongoing devastation in Myanmar. The best thing that you can do if you’re feeling worried about earthquakes and tsunami is to take steps to be prepared, for example making a plan with your household, checking if you’re in a tsunami zone, or practising your drop, cover, and hold. Even if it’s only one step, it’ll help ease your worry now and help you cope better if something does happen.

This magnitude 7.0 earthquake occurred to the east of the Tongan islands at a depth of about 30 km. This is relatively shallow for earthquakes in this region and explains why the shaking was strong in Tonga. Earthquakes are very common in this area and happen due to the Tonga-Kermadec subduction zone, an extension of the Hikurangi subduction zone which lies under the North Island of New Zealand. Analysis has shown that this earthquake likely occurred along the interface between the Pacific and Australian plate. There have already been aftershocks, and these will continue for the near future.

This morning's magnitude 7.0 earthquake had its epicentre 160 km northwest of Tongatapu. Since 1900, 40 magnitude 7.5+ earthquakes have been recorded on the long subduction zone stretching from Tonga to New Zealand. Most of these large earthquakes were on the northern end of this subduction zone, where the convergence of the pacific plate subducting under the Australian plate can reach speeds of 24 cm per year. There is no longer a tsunami warning, and early indications suggest that damage may be minor.

"In contrast, this earthquake follows the devastating magnitude 7.7 event in Myanmar last week on a strike/slip fault part of large-scale collision between the Indian plate and the Eurasian plate.

"The short time between these large earthquakes often raises the question about any relationship between the events. Recent research on so-called dynamically triggered earthquakes investigates this possibility. While it is impossible to determine whether the Tonga earthquake was triggered by the Myanmar event, there is statistical evidence this sort of phenomenon can co-occur. A blog for our school network of seismometers contains a reference to a Nature paper discussing when and how dynamically triggered earthquakes can happen.