9/2/2023 0 Comments New zealand quakeResearch is ongoing and these probabilities will continue to be refined and updated over time as new evidence and data becomes available, but what we know now is pretty startling anyway. The latest research and data available now indicate the probability of an earthquake of a large earthquake on the southern end of the Hikurangi Subduction Zone in the next 50 years is about 25%. However, because it under water and harder to get to, there is a lot less known about this subduction zone. The Hikurangi Subduction Zone represents an even bigger hazard to New Zealand than the Alpine Fault. The latest research puts the probability of a magnitude 8+ earthquake on the Alpine Fault in the next 50 years at 75%. Scientists now have records going back about 8000 years on this fault and movement seems to be fairly consistent in both size and frequency. The Alpine Fault is the South Island’s most significant natural hazard. Together with a series of faults through the Marlborough region, the Alpine Fault marks the on-land part of New Zealand’s plate boundary and involves a combination of mostly sidewards movement, but also some squeezing across the island to uplift the Southern Alps. The Hikurangi trench also joins up with the Kermadec Trench further north. Between these subduction zones, in the South Island, there is a massive link structure known as the Alpine Fault. The phenomenon of one tectonic plate being pushed under another is called ‘subduction’ and New Zealand’s plate boundary has two areas where this occurs – the Hikurangi Trench (offshore to the north-east of the North Island) and the Puysegur Trench (offshore to the south-west of the South Island). 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. 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.
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