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AF8 Science Talk – Impacts of an Alpine Fault Quake

AF8 Science Talk – Impacts of an Alpine Fault Quake


My name’s Tom Wilson I’m an Associate
Professor of Disaster Risk and Resilience at the University of Canterbury. I’m going to give a presentation today looking at some of the impacts that we expect might happen from a future Alpine Fault earthquake. I’m presenting on behalf of a very large team of disaster risk scientists from from all around New Zealand. What I’m going to focus on is looking at the consequences or the impacts of a future Alpine Fault earthquake We’ve already had covered a lot of the hazard information, so things around the frequency or the likelihood of a future event, how big that that future Alpine Fault earthquake might be, and we’ve had a great presentation looking at what the intensity of those effects might be across the South Island
and what the size of that hazard footprint potentially it could be. But I’m going to focus on this this other aspect here, and the reason we’re going to focus on consequences or the impacts is that if we can estimate what those consequences might be it allows us to perhaps more accurately develop
appropriate mitigation and preparedness strategies for that future disaster
event, and we really draw on a lot of previous research which has looked at
the need for developing specialised, sector specific information for pre- and
post-disaster event outcomes, and that’s that’s what we all sort of get into a
little bit of today. So to just help set the scene, this is how we go about assessing disaster impacts. So we need to take aspects of what’s the hazardous event that we’re going to potentially experience in the future in this
case we’re thinking about the Alpine Fault and potential scenario of what
might happen there but we also need to consider what societal elements might be exposed to that disaster event so that could be anything like buildings, people, critical infrastructure; could be our economy; could be any aspect of society
that we’re interested in assessing. And the thing which brings it together
is how we pull together that vulnerability so what’s the
vulnerability of their asset or element when it’s exposed to that hazard intensity. So in this case, if we take example of the building that you’re in as you’re watching this, how might that building and what are its
attributes how might it withstand the shaking intensity that it
experiences from a future earthquake. So as we heard from Brendon Bradley, if it’s predominantly masonry construction with no reinforcements it’s likely to perform
quite poorly and may be quite badly damaged. Whereas if we have a very strong
ductile modern construction we’d hope that it would withstand this that event
much more effectively. So by combining those three different aspects that allows us to assess what those those impacts will be. Okay, so just to remind
you again what we’re predominantly using is we’re assessing the impacts from a
future Alpine Fault earthquake. We’re going to use the scenario of where
there’s been a southern or a rupture of the southern part of the Alpine Fault
and it’s ruptured up north west, sorry northeast, along the Alpine Fault
strike and creating that scenario of shaking progressively moving up
across the north east of the South Island and out and across. You’ll remember that video that Brendon Bradley has shown looking at how that’s
ground motion and potentially might move across the South Island and where that
those shaking effects might be so that’s that’s the the hazard footprint and
shaking intensity that we’ll use for a lot of our disaster impact assessment
today but the thing that we’re also needing to consider is that earthquakes
aren’t all just about the ground shaking which is produced whilst they might
produce a great big rock and shake that we experience they also cause what we
call secondary hazards so things like landslides, liquefaction and
even potentially tsunami. So I’ve got a little animation here. So just showing as we see this cascading hazard event from an earthquake. So we have a big earthquake
as we can see here on the image here on the bottom left and that might cause a
landslide especially if we’re in mountainous terrain, where landslides can come down
and in this case it looks like it’s blocked a valley. So the next thing is
it’s blocked out valley, the drainage system, or the river there, has been blocked and a quake lake forms behind it and then potentially it might break out catastrophically and we have that dam break flood. So the series of cascading events is something that we have seen in New Zealand. Particularly
with the recent Kaikōura/Hurunui earthquake in North Canterbury or in the
northern part of the South Island this was a major issue which occurred across
much of the affected areas. Now the important thing when we’re thinking
about disasters, especially earthquake disasters, and countries like New Zealand
is it often these secondary hazards can cause some of the most devastating consequences. Much of New Zealand has been relatively well built through use of building codes. Buildings, typically, hold up pretty well
particularly by global standards when we have large earthquake events. But these secondary hazards they can be very difficult to design for and often may not have even been considered during the design phase. So, as we look at examples from around the world such as the Boxing Day Indian Ocean tsunami from 2004, and various earthquakes
that we’ve had in New Zealand such as the Canterbury Earthquake sequence the Kaikōura/Hurunui earthquake sequence it’s been these secondary hazards which have led to some of the greatest monetary and social impacts from these disasters. So that’s something that we’ve put a lot of effort into thinking about for a future Alpine Fault earthquake. So one of the pillars for this was looking at producing a co-seismic landslide model. Some great work by Tom Robinson and others has developed this model looking at using
those inputs from the likes of Brendon Bradley and GNS Science and others,
using those ground motion simulations to forecast or estimate where co-seismic
land sliding might occur and that’s what you’re seeing
on the left here of your screen of this model of the South Island
looking at combining factors such as the topography, the geology, how steep that
that topography might be when it interacts with this the strong ground
motion and this map is showing an estimate of relative level of hazard of
of land sliding, which becomes quite useful when we’re trying to estimate what the potential consequences of these things might be. This image here on the righthand-side has an example of landslide dam following the 2016 Kaikōura/Hurunui earthquake. Just to give a little bit of real-world aspects to it. So, these are things that particularly the
co-seismic landslides these are things which we worry about considerably in the
immediate aftermath of earthquake event. Particularly in a mountainous terrain
like much of the South Island is with our beautiful Southern Alps. So those immediate effects can be quite damaging
and impactful especially for anyone that’s exposed to where those landslides might occur and also our critical infrastructure services and I’ll talk a little bit more about that in a minute. But something we also need to keep in mind is that this isn’t going to be just a small snapshot, a small time window disaster The geomorphic consequences of this event may continue for many years
afterwards. This is a little taster where this kind of weird little series of grey
aerial photos here give us a little bit of an example of what might happen. So what we’re showing here is the Poerua River on the West Coast of New Zealand So what happened here in 1999 was that Mount Adams which is a large
mountain and right in the middle of the Southern Alps quite close to the
Alpine Fault. It experienced a very large landslide. It wasn’t due to
earthquakes it was just due to very high rainfall at the time and what happened
as that landslide came down and blocked the upper catchment of the Poerua River
and behind it large, large landslide dam was formed. And in the aftermath and then
it eventually broke out through that that landslide dam and carried a huge
amount of sediment downstream. Now what you’re seeing here is a series of air photos of the catchment of the floodplain of
the Poerua River, just as it’s exiting out of the the range front of the Southern Alps. So you can see in 1987 this was the situation in 1999 where the Poerua River
was largely immobile or largely constrained on the southern part of the floodplain, we’re looking here towards the south, by a series of stop banks. So Poerua River is just constrained there nicely on the southern extent of the floodplain. But after that breakout in 1999 we can see this air photo from 2001 that a huge amount of sediment has been brought down, the river has a vault or broken out of those stock banks, out of their active
channel, and has spread out across its floodplain and as we look through 2002
and down to 2005 we can see progressively more and more of that
floodplain has been inundated and covered by that new active channel and
flood channels of the of the river and a large amount of sediment has been
distributed across. This had severe consequences for the farm that was operating in that location it was a beautiful high productivity pastoral
farm very fertile soils and of course any potential implications for critical
infrastructure downstream as well bridges or that sort of thing.
So that’s a little bit of a snapshot of what we might potentially see on quite a
grand scale after a future Alpine Fault earthquake. We may have these types of
landslides blocking catchments or river systems across much of the Southern Alps
both on the west and eastern side So, something really, to potentially, to consider. Okay, so thinking about our coming back to our disaster impact
assessment model now we need to think about what’s exposed so one of the
things which we’re most interested in or a critical aspect is our essential
infrastructure systems. So our state highways are crucial for modern
operation of society. In the South Island in particular they used for general
access obviously but particularly important for our main industry with
tourism and agriculture with dairy farming, pastoral farming and so on and
even our mining industries across on the West Coast and particularly getting that product across to the East Coast deepwater ports. Electricity or electrical power of course is important for everybody and with much of New Zealand’s hydroelectric power generation based
down in the southern part of the South Island moving that energy up towards the
north of course is an important part of that grid. And, much of those tourism, dairy and mining worth a large component of New Zealand’s GDP Now the problem with our long skinny island, with the South Island is that these networks are also long and skinny. There’s very little redundancy
for both our state highway networks and for our electrical networks as well,
especially the big transmission networks. And often especially when accessing
remoter parts such as the West Coast and in other areas, is that they these
networks have to pass through very steep landslide prone terrain in very
very active environments. so disruption to roads and the power network is likely to hinder disaster response both in the short and the long term. Now some important lessons need to be drawn from from this for when we’re thinking about
a future Alpine Fault earthquake from what we’ve experienced with the Kaikōura/Hurunui earthquake sequence. Thinking across things from casually estimation,
building damage and function, the social impacts and economic consequences from
the loss of these critical lifelines. Some of the work that we’ve been really focused on and Tom Robinson’s been the real lead on this Has been looking at what’s the potential exposure of our state highway network to co-seismic land sliding So the map that we’re looking at here is
looking at the exposure of the likelihood of small sections, at one
kilometer and length, of road being effected by a particular landslide. Now, the red colors are where there’s very relative high exposure and the softer
colder colors and the blue that’s where we estimate there to be much lower
likelihood of exposure and hopefully what leaps out to you is immediately we
can see our Alpine passes are highly exposed and so, probably
unsurprisingly, Arthur’s, Lewis Pass, the Fox Hills around Franz Josef and
Fox Glaciers, Haast Pass and Milford Road all really highlighted as as being quite
potentially severely or highly exposed But perhaps also something that we want
to take home from this is that it cumulatively suggests that there’s likely to be large tracts of the South Island which may be
isolated for potentially considerable periods of time. I’ll get into talking
about restoration of these assets a little bit later in the talk but just
keep that access issue in mind as we go forward. The next big sector that we’re
interested in is the electrical infrastructure. So as I said before much
of a power is generated in southern portion of the South Island, particularly
down on the Waitaki River system and lovely shot here of Benmore Dam on a
beautiful, spectacular day But again if we apply our co-seismic landslide model
over the top of this we can see that much of that main trunk of
transmission network is relatively clear until we start to get up into the
northern part of the South Island up and around North Canterbury and into
Marlborough and so it has important applications in terms of our ability to
move electricity towards North Ireland but also to receive electricity from the
North Ireland towards the south if we would have disruption in the southern parts. I’d also draw your attention, looking at this map to again, to the relatively high exposure to those transmission lines leading into the West
Coast so again we might potentially have tracts of the South Island which might
be without power potentially for large periods of time as these landslides
potentially impact pylons and poles and the ground shaking or the landslides
may impact some of our transformers leading to network outages. As we’ve heard from Caroline, a substantial concern is with our hydroelectric power dams is when they do receive a large shake, is that they do automatically shut down looking to
protect the asset hopefully and checks and bits and pieces will be required afterwards. But progressively being able to restart those dams, particularly if many of those dams have an inability to restart themselves, may be a challenge in the aftermath of a large regional
earthquake such as an Alpine Fault. Also whether we have
a lot of potential ground shaking affecting the inter-island connection
between the South Island and the North Island may start to have implications as
to whether we can receive or will give electricity into the North Island so
potential a few issues with their electricity network there. And the third one which we wanted to concentrate on here was the importance of to our
telecommunications network. So much of our telecommunications network has
either in our buried cables or with our cellular network with our transmission
stations scattered across the South Island. telecommunications are
increasingly important for post disaster response
coordination a huge amount of reliance being able to share information through
those potential networks but increasingly the expectation from
society to have access to telecommunications in that post
disaster context is growing with every event that we observe and so the ability
for our community well-being to be fostered and enhanced as an important
dimension to consider here as well. What we’re concerned about with the loss of
electrical supply to parts of the South Island and potentially on a grand
regional scale will also be that loss of telecommunications equipment where they’re
reliant on electricity to to operate and so combined with the loss of or
potential loss of our transportation network is we may not be able to provide
those sites with electrical supply and there may not be able to access them
with generators and fuel to fund to power those generators and potentially
well it’s estimated to be one of the largest impacts that we might see for
the telecommunications sector. So a few challenges to work through there. Now, when thinking about restoring these infrastructure networks it’s relatively
uncertain business of trying to estimate how quickly and where they
might be restored. It will be very dependent on the context of the nature of the disaster the time of which populations or communities require
that restoration of those networks first and we are even those resources that can
restore those networks are located. But I think it’s simply as we’ve been
discussing with a lot of the infrastructure managers and Civil
Defence professionals is that restoration of the highways,
telecommunications and the electricity networks will be a top priority in the
aftermath of a disaster like this. But the challenge that we are faced with is
the ongoing aftershock sequence, ongoing landslides which might occur in particular in areas such as Arthur’s
Pass and so it may make some areas particularly dangerous and challenging
to restore those networks for months to potentially even years in some cases. The 2016 Kaikōura/Hurunui earthquake and the restoration of the state highway network and rail networks have provided essential examples of this. But again likely to see tens to hundreds of similar landslides and the alpine passes
and if you can think it from the perspective of that coastal stretch just north of Kaikōura or around Kaikōura as those transport networks for we’re impacted they only had one one mountain set on them whereas in our alpine passes we have steep terrain on both sides. So it potentially might be even more challenging to restore those networks. An example here is when we’re thinking about modelling what these impacts might look
like, working with Transpower, it takes around about two days to restore a
single pylon that has been damaged or destroyed. One of the preconditions there
is safe ground access is required first and depending on which modelling that
you want to look at we’d estimate around about 30 pylons may
potentially be damaged or destroyed in Arthur’s Pass alone from co-seismic
landslides. So using that equation it could be up to a year before that power
line through Arthur’s Pass may be restored. So just working through the
practicalities of restoring these assets may be quite a considerable task. Moving on to casualty and welfare
impacts an event like this, unfortunately, is likely to cause
casualties. Where we may sustain deaths and and injuries and also lead to a
range of potential welfare impacts both immediately and also in the longer term.
The impacts are likely to be dependent on a range of factors and one of the
areas which can inform us a lot with us is the recent experience from the
Canterbury Earthquake sequence and the Kaikōura/Hurunui earthquake experience of
looking at what type of communities were effected the time of day and so on. So we know the characteristics of the earthquake will be important it’s a
primary driver of where the hazard footprint might be what shaking
intensities might be exposed but and that’s something that we as a society we
can’t really control that. But what we can control is what assets or what
elements are exposed, what people and communities are exposed, and particularly
what’s their vulnerability. So we know that things like the time of day of the
earthquake will be an important determinant on what impacts occur to
people the time of year and particularly what buildings they are in or nearby. So some of the examples that we’ve seen with the likes of Christchurch where
people inhabiting or being located close by to buildings which are potentially
having its of bits of their structure falling off them leading to impacts to
people or non structural damage with non-structural elements falling within
the buildings may also be an issue. And those are things that we can
tangibly control now and hopefully make good before a future event. One of the other big challenges that we have when we’re considering casualty
estimation in the South Island is our transient populations and so what we
mean by that is people that are moving around might not have a fixed location
such as our tourists for example. New Zealand is an absolute
tourism boom at the moment. From a dollar value I think our most important single economic industry at present, and to give some context we had 3.6 million international arrivals for the year ending in August 2017, which is a
huge number coming through. I think it’s been estimated that the West Coast alone
has 1.5 million tourists moving through it every year over the last couple of
years. So a large number of people who aren’t familiar with the environments
who are potentially highly vulnerable may be in some very unfortunate places
if this event occurs when they they happen to be there.
Particularly if we’re thinking in terms of a response at the height of the
tourism season this could really be quite a challenge for Emergency Management
agencies and organisations to deal with. Another aspect that we we
have which we know influences the outcome is the behavior of people so how
do people perform during that disaster event and in the immediate aftermath
will have an important implication, or have an important influence I should say,
on what their outcomes will be so there’s a strong role for education to
to help inform aspects of this. The loss of essential services. So loss of water supply, power, loss of transportation access, and telecommunications will also
influence the outcomes for people exposed, our communities that are
exposed, to this disaster event so it’s really a I guess a multidisciplinary
issue that we need to be dealing with. The level of building damage
which are building sustain, are they still habitable for people to reside in, do they have the essentials of life to be able to inhabit within them all big challenges for our welfare
managers to and agencies to deal with in the aftermath and events such as this. And again just reminding and certainly not trying to scaremonger, but just
thinking of the scale of this potential event which we might be faced
with now, hence that importance of planning. And certainly through the
the planning and scientific processes that we’ve been undertaking as part of
Project AF8 is really a strong identification that isolated communities
whether it be through lack of access or lack of essential services or lack of
food and water for example may be one of the biggest challenges that we have
in the aftermath of an earthquake like this, and so that’s where a lot of the
the scientific work is is looking to try and help inform what the outcomes might
be and what are the best ways to mitigate those those potential impacts. One thing I haven’t focused on much with this for now and mainly due to time is
the likely socio-economic impacts that we may sustain from an earthquake like
this there’s no doubt that there will be disruption to the economy but a lot of
work is currently underway looking at what are those potential recovery
regimes and particularly policy implements that we can use to hopefully
effectively come through a disaster like this, and it might be a story for another day. So just a few take-home messages from me. Just coming back to some of the other talks that we’ve had in this series: There’s strong evidence for those 27 large earthquakes on the Alpine Fault which have occurred very regularly
over the last 8,000 years. A very high chance the next day earthquake
will be a magnitude 8. This will occur again in the future
and it’s likely to be a very large earthquake. This gives us strong impetus
from a hazard point of view. There’s likely to be widespread
secondary hazards we’ve seen that from the Kaikoura/Hurunui earthquake sequence which is a very good analogy for what we might see in the future this should
provide us with some essential lessons going forward. There are likely to be issues both in the immediacy of the event and in the long-term aftermath. The effects will extend across the South Island and potentially into the lower North Island, so this will be something that the nation of New Zealand needs to consider very strongly. Potentially, there’ll be extended periods
where many communities and sometimes very large communities will be without
essential services, we must plan for that and look to reduce those effects as much as possible. There are likely to be casualties, but anything that we can do now particularly through education through building codes and so on will
stand us in good stead so the opportunity is now to make those changes
and especially considering what are we going to do with those vulnerable
transient populations in those isolated areas. Many areas are likely to be isolated
for potentially long periods of time and they will be dealing with various
challenges themselves how can we empower them to most effectively respond, how can they be equipped with the
tools the resources and the knowledge to most effectively operate in that
new reality that they’ll be faced with. But if nothing else, that you’ve taken
from this series of talks is that an Alpine Fault earthquake will happen again
and potentially the consequences will be be quite challenging so preparation now
is absolutely key. Thank you so much for your interest and if you’ve got any questions
we’d be very happy to entertain them.

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