Getting ready for the Alpine Fault


It is New Zealand’s biggest seismic hazard, short of a Hikurangi Trench subduction zone rupture. The Alpine Fault earthquake that is expected to occur in the next 50-100 years has been well publicized. But how much are communities close to the fault doing to prepare for a magnitude 8.0+ earthquake?

The Alpine Fault, New Zealand’s answer to the well known San Andreas Fault in California, is the tectonic plate boundary between the Pacific Plate and the Australian Plate where they intersect in the South Island. Every 300 years or so this fault line ruptures in a magnitude 8 earthquake. A sequence of 24 events over the last 8,000 years points to earthquakes in 1100AD, 1450AD, 1620AD and finally around 1717AD,

No part of the South Island will be spared prolonged shaking. Many people, especially i in the lower North Island, will also notice the earthquake. Shaking intensities along the rupturing segment of fault are likely to be up to MMX, which is strong enough to heavily  damage all structures, with many failing and large objects such as televisions and microwaves being moved about. Liquefaction, lateral spreading, landslides and seiching of lake bodies will occur as well.

Alpine Fault Magnitude 8 is a collaborative and ongoing project to improve the readiness of councils across the South Island in terms of their ability to respond to such an event. It has buy in from emergency services, Civil Defence, social groups, the N.Z.D.F., agencies working with lifeline infrastructure and others. The aim is to improve modelling of the potential hazard, engage emergency management and planning experts and use the knowledge gleaned to fill gaps about how to respond.

I anticipate that much of the work that has been done will have been brought into sharp focus by the Kaikoura earthquake in 2016. This was the largest onshore earthquake to hit New Zealand since Murchison in 1929. It caused widespread damage across the northern South Island and lower North Island. The quake exposed weaknesses in transport arrangements with both the railway line and State Highway 1 closed – traffic had to be rerouted through the Lewis Pass in order to reach Picton.

Despite the Kaikoura earthquake and lingering shadow of the Christchurch earthquake, not all councils appear keen to progress their disaster planning. Westland District Council found itself in hot water in 2016 for rejecting Plan Change 7, which sought to address the planning issues that Franz Josef township finds itself confronting. The township straddles the Alpine Fault, which is clearly visible from the air as a crude gash in the landscape. Critics pointed out that the council has a duty of care to all in the District and that by failing to address the risks posed, it leaves itself open to court action by anyone in the District at the time of such an earthquake.

Yet the risk remains. Other councils are pressing ahead with their own plans individually, to be fed into the overall A.F.8. planning framework. It is a proactive council that stands the best chance of success, for no one knows when 300 years of seismic stress on the Alpine Fault will give up the ghost. The only certainty is that with the same confidence that darkness will come into a room when the light goes out, one can conclude it is inevitable.

New Zealand’s megathrust earthquake problem


Scientists are drilling into the tectonic plate boundary off the coast of the North Island. They are trying to find out how close it is to rupturing and looking for clues to indicate levels of tectonic stress.

This is not something anyone should be surprised about. As a nation straddling an active tectonic plate boundary with both strike slip and dipping tectonic plate interface, we are subject to a range of future seismic hazards that at the moment are low risk, high consequence. Those unfortunately are drifting gradually towards high probability/high consequence – the longer it takes for one to happen the worse it will be when it happens.

This is why much research is underway both on land and at sea to understand the hazard posed by the tectonic plate boundary. Not only that, but to also understand how the tectonic interface works, whether there are geophysical or geochemical changes happening in the rock strata that might indicate how much time we have left.

A megathrust earthquake is one involving a large segment of dipping tectonic plate boundary that ruptures at once. Examples include the Tohoku magnitude 9.0 off the coast of Japan in 2011, the 2004 Sunda earthquake that unleashed a magnitude 9.3 earthquake. New Zealand has not had a megathrust earthquake in recent centuries.

This would be a devastating event if it happened in New Zealand. The energy released in the event would be immense – possibly 2000 times more than the It would involve the Hikurangi Trench rupturing from off the east coast of the South Island up past East Cape. The potential magnitude of the earthquake could be anywhere between M8.5 and M9.0. It would involve probably 5 minutes of sustained shaking – 3 minutes longer than the 2016 Kaikoura earthquake and comparable in length to the 2010 Chilean M8.8 event.

The earthquake would very likely trigger a tsunami. The major megathrust earthquakes of the last century have all triggered destructive tsunami – the worst in terms of casualties and overall damage without doubt being the 2004 Sunda event and the 2011 Tohoku event.

The message for coastal areas of New Zealand since the Kaikoura earthquake has not changed: LONG (lasting more than a minute) AND STRONG (can’t stand up)? GET GONE. And for all people caught in an earthquake that is not over in a few seconds and especially if at that point it seems to intensify, the message is “DROP (to your knees). COVER (under a doorway or desk). HOLD (on)”.

Time for coastal planners to take climate change seriously


For the people trying to get away from Ex-Tropical Cyclone Fehi’s storm surge, it was all too real. For the people in small coastal towns along the West Coast watching the angry seas smashing what in some cases were the only roads in and out of their townships, the thoughts of being cut off must have been nerve wracking. As communities clean up and look to the future, it is time to ask just how good are the contingency plans for future storms, and whether planners have made adequate provision for such events.

Given that high intensity but relatively short duration storm events seem to be becoming a regular occurrence, how well prepared are we for the effects of climate change on the marine environment including how oceans contribute to storms? In January 2017, we had a “weather bomb” of highly damaging winds and substantial heavy rain in the Southern Alps; Cyclone Debbie, which caused widespread flooding in the Bay of Plenty; Cyclone Cook, which tracked quite quickly past New Zealand, without directly crossing the country. There was also several significant winter storms.

There were a number of facets of ex-Tropical Cyclone Fehi that I found concerning as someone who has studied natural hazards:

  1. Granted it was only a Category 1 Tropical Cyclone, Fehi’s relatively rapid evolution from a tropical depression in the Coral Sea to a
  2. Despite having lost its status as a Tropical Cyclone, the remnants of Fehi still managed to kick up 150km/h winds. It still managed to drop over 200mm of rain in a day and in some cases up to nearly 300mm
  3. The storm surge – granted it was exacerbated by king tides caused by a rare blue super moon – was punishing in many small settlements such as Ngakawau, Granity and Hector on the West Coast, north of Westport

It is true that councils have started planning for climate change on the coastal environment and the elevated risk posed by storms. Some communities are having to turn to their ratepayer base for more money to help fund expensive coastal works, such as sea walls and helping maintain existing natural features such as sand dunes.

Over the last 20 or so years I have been watching the tidal gauge charts at Lyttelton that have been appearing in The Press. 20 years ago, the lower end of the range was 0.1m and the top end of the range seemed to be consistently around 2.5 metres on king tides. Outside of that, the range could be as small as 0.5m-2.0m. Today in 2018, the range seems to be between 0.1m-2.7m. I am not necessarily suggesting this is due to changes in sea level – it could simply be that the tidal gauges today are better calibrated to detect more minute changes, and thus 0.1m-2.7m +/- all along.

This is important to know because hazard planners plan for the worst case scenario – and hope that reality is something a bit less severe. The worst case scenario would presumably be a storm – not necessarily a tropical cyclone, as a deep low pressure system with its origins in the Southern Ocean can cause much damage – with a surge, coinciding with king tides. Such a storm happened last week.

Moving forward, the damage caused by Fehi, aside from causing insurance companies and Civil Defence much grief, also kick up some serious planning issues. Are, for example, Regional Plans adequately tooled to deal with land zoning issues that may arise from coastal properties no longer being suitable for occupation? Does the New Zealand Coastal Policy Statement pay the due regard now needed to coastal hazards and climate change? And given Fehi could have been a stronger Cyclone, but mercifully was not, was what happened last week really a taste of the “worst case” scenario?

It is time to start asking and attempting to answer these questions.

 

Public not trusting emergency evacuation warnings


Civil Defence are concerned that people are becoming blase about disaster evacuation warnings. This particularly pertains to tsunami warnings because of the absence of a damaging tsunami event striking New Zealand. Social media critics are claiming that Civil Defence cry wolf over evacuation alerts and some are engaging in the dangerous and irresponsible practice of sowing division that makes people uncertain in times when certainty is necessary.

But one day a damaging tsunami will occur. The ones that have happened in recent decades have fortunately arrived at times in New Zealand when the tide was out far enough that the waves lost all of their energy making up ground in the tidal zone, or more likely were never going to be very large in the first place and – high tide or not – were simply out of energy when they got to New Zealand.

But picture this. A major earthquake has hit the South American west coast on the tectonic plate boundary off the Chilean coast. A Pacific wide tsunami warning has been issued. The waves will start hitting New Zealand about 13-15 hours from now. The largest wave comes ashore in Chile 10 metres high and causes heavy loss of life and damage.

The tide is coming in in Lyttelton when the first warnings are issued about with about 10 hours leeway. The waves will begin to strike on a rising tide. Based on computer modelling the waves are likely to reach 2-3 metres. Over the next several hours the warnings are refined as data comes in. Major damage has been done along the west coast of South America as far north as Colombia and there are waves heading for Hawaii, New Zealand, Fiji.

People are generally complying with the authorities evacuation advice. Despite the confusion about arrival times and wave size, people accept that a warning has been issued and they need to move to safer ground.

But on social media, disgruntled people are accusing Civil Defence of crying wolf. They say past tsunami’s turned out to be nothing and this one will be nothing as well – why should they worry?

There are some basic rules about tsunami’s that everyone needs to know:

  • There is MORE than one wave. Some have up to 8
  • The first wave is RARELY the biggest. The 1960 Chilean tsunami was triggered by a massive earthquake and the third wave was the biggest
  • The topography of the ocean floor means every tsunami behaves differently – is it for example a long narrow bay with a shallow dipping sea bed? In that case you will probably see the waves coming sometime before they get to you. Or is it an open beach with a steep drop off? In that case the waves will not be obvious until it is too late and hit the coast with significant speed that you will not be able to outrun
  • Do NOT go back in between waves as you won’t have time to get away. In tsunami events elsewhere this has cost people their lives
  • Be prepared to be gone for several hours
  • Stay away from coastal water features such as river mouths, estuaries and lagoons lest you get cut off

 

Post-earthquake flood woes return in Christchurch


I do not remember though the Heathcote River or the Avon River overflowing as frequently as they seem to now. Significant overflow events have occurred in virtually every year since the earthquakes. Some of the were on relatively insignificant rainfall events such as one in early 2012 which occurred on the back of 90 minutes heavy rain. More serious (considerably more serious to be honest)events occurred in August 2012, June 2013 during a significant winter storm, significant storms in March and April 2014, and finally two storms just week apart in July 2017 (the last one being the one on Friday-Saturday just gone).

I visited both rivers on Saturday to see for myself the extent of the flooding. Both had road closures in place, or would shortly after I passed. The photos in this article are ones I took on a brief drive on Saturday morning to see how bad the flooding was. I deliberately avoided the lower part of both rivers and the estuary because significant road closures were in force at this point and I thought it would just hold up essential traffic.

Avon River (Wairarapa Terrace), R. Glennie

To be fair, it is worse in the lower reaches of both rivers near the estuary, where some parts have dropped by up to 50 centimetres. This means even a big king tide can now cause flooding, without any rain falling. So it was unfortunate then that 2.7m tide, which is the top of the tidal range around Christchurch, was due in Lyttelton at 1515 hours on

Avon River looking upstream, R. Glennie

Saturday.

But we have known about the flood hazard since the quakes. It existed before the 2010-11 earthquake sequence began, but was then largely understood to originate from the Waimakariri River, on whose flood plain the city is located. We have invested millions in reducing the flood risk around Flockton (Floodton)Basin, a low lying area east of the Palms Shopping Centre, where land subsided around the upper reaches of the tidal zone and does not drain easily as a result.

Heathcote River at Tennyson Street, R. Glennie

But it is not just the flooding that is the problem. Following the flooding is sometimes even more stressful as the insurance claims are sorted out, the houses cleaned out and the sanitation made safe again. Often carpet has to be ripped up and electronics replaced.

Heathcote River at Colombo Street, R. Glennie

Perhaps it is time to face an uncomfortable truth. The flood risk has significantly increased in these low lying areas. It is not going to decrease unless dwellings are either raised or moved. Yes it will cause a lot of stress for locals, but one only has to look at the number of times significant flood events have occurred since the earthquakes tells that perhaps these streets should not be occupied, or they can be occupied, but the insurance must be significantly more rigorous.  But one thing is for certain: the flood hazard has changed and we need to adjust accordingly.