This is a complicated boundary and the different ways in which the plates converge along its length, pushed under or moving alongside each other, result in a variety of earthquake types. The good news is that each big earthquake increases our understanding of the inner workings of our landscape and how best to prepare for the next one.Īround the world, earthquakes are concentrated on tectonic plate boundaries and New Zealand sits right on top of part of the boundary between the Australian and Pacific plates – it’s why we have all those lovely mountains and hot pools. The map below shows the most significant quakes recorded since 1848, many of which will be familiar to you. Most casualties in earthquakes are from building collapse and/or fire. Māori oral history includes many references to the shaking of Papatuānuku, and there is a wealth of geological evidence that reveals when some of our big ones occurred (including the last rupture of the Alpine Fault in 1717). While earthquakes have been around for as long as New Zealand has existed, the human impacts have increased over the last 200 years with increased urbanisation and population. Our little islands have experienced many large earthquakes in the past. This was an event of international significance – before this we didn’t know that earthquakes caused shifts of the landscape! This earthquake also caused a tsunami in Cook Strait, which inundated many buildings around Wellington Harbour. Some of the land around Wellington was uplifted by 6.4m and in other places it moved 18m horizontally. The largest earthquake ever recorded in New Zealand was the magnitude 8.2 quake on the Wairarapa Fault in January 1855. A very large earthquake in Fiordland would hardly be noticed beyond Te Anau and surrounding settlements, whereas a much moderate one in Wellington would have serious implications for a much bigger population and the condensed urban environment. Location – Obviously, the more remote an earthquake, the fewer impacts for people. Secondary hazards – Landslides, tsunami, liquefaction, aftershocks, fire and rockfall are common secondary hazards associated with large earthquakes. In winter, for example, woodfires can create a hazardous situation during an earthquake and hypothermia becomes a greater risk for those with limited shelter in the aftermath. Time – the time of day and time of year an earthquake takes place can impact the number of casualties, damage and ongoing effects. soft sediments can experience liquefaction.īuilding Construction – with every earthquake, something new is learned by engineers and building designers about how they will react to a quake and this is translated into the New Zealand Building code. Ground conditions – different ground conditions (rock and soil types) react to shaking differently, e.g. The shallower the earthquake the closer it is to us on the surface and so the more intense the shaking. New Zealand sits on the seismically active “ Ring of Fire” around the Pacific Ocean, where about 90 per cent of the world’s earthquakes occur.Ī magnitude 6.3 earthquake struck 10 kilometres from Christchurch’s central business district in 2011, killing 185 people and injuring thousands more.But when it comes to impacts, the magnitude of an earthquake isn't the only factor, here are some others:ĭepth – earthquakes can occur anywhere from the surface to 700km deep. The strongest aftershock recorded so far was magnitude 6.3. The region has already experienced more than 300 aftershocks, half of which have been magnitude 4 or greater. Nevertheless, it could set off the closer Hope Fault, which branches off the Alpine Fault, he says. However, Ristau believes Monday’s earthquake is probably too far away from the Alpine Fault to have a direct effect. If the 600-kilometre fault ruptures, it will produce one of the biggest earthquakes in New Zealand since European settlement, says GNS Science. The giant Alpine Fault borders the South Island and splays into many faults through the North Island, he says. The stress change could trigger a powerful earthquake at the interface between the Australian and Pacific plates, known as the Alpine Fault, says Kevin McCue at Central Queensland University. The South Island was thrust up over the Pacific plate with some sideways slip. Preliminary data show the earthquake occurred on a previously unknown fault near the interface of the Australian and Pacific tectonic plates. Waves measuring 2.5 metres hit the coast soon afterwards, but further, larger waves of up to 5 metres that were feared didn’t happen. The quake triggered a tsunami warning that was later cancelled.
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