The Alpine Fault Earthquake: Natural Event and Human Consequences

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The Alpine Fault EarthquakeNatural Event and
Human Consequences
UPDATE

• Mauri McSaveney
• GNS Science

Tim Davies Canterbury University
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Outline

• Whats new?

• The next Great Alpine Fault Earthquake
• Why
• Where
• When
• How big
• Associated seismicity
• Consequences (immediate and delayed)
• In the landscape
• In society
• Mitigation
• Now
• Later

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Whats new?
1. The Christchurch earthquakes what do they
tell us?
2. Probabilities dont help much
3. New Alpine fault information
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What does the Christchurch experience tell us?
1. Bad stuff DOES happen the Alpine fault WILL
rupture, so will the Wellington fault
2. The Chch earthquakes were small we are VERY
vulnerable. The Alpine fault will be 60 x more
energetic
3. Most big earthquakes occur on previously
unknown faults but the Alpine and Wellington
faults will be exceptions
4. Liquefaction and site effects are a VERY big
deal
5. Recovery/rebuilding takes much longer than
expected
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Probabilities are based on past data and dont
help much earthquakes are UNPREDICTABLE in time
and magnitude
So what should we plan for?
What we know CAN happen
At ANY time
Chch was much worse than the previous worst-case
scenario for the city
So was the recent Chile earthquake the maximum
credible magnitude was 8.4, the event was 8.8
250 more powerful.
The Japan earthquake of 11 March was M 9.0 the
expected magnitude was 8.5
Things may be worse than we think...
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New Alpine fault information depth of seismic
rupture 13-18 km, not 7-13 km as previously
thought (Beavan et al., 2010).
This means the energy released is greater than
previously thought may be Mw 8.2 instead of 8...
However it appears likely that the rupture will
not initiate in the south and propagate
northwards good news?
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Our place on the planets scheme of things
Earth has a mobile surface divided into tectonic
plates
The New Zealand continent is on one of the
plate boundaries The Alpine fault connects two
subduction margins where ocean floor descends
into the Earths mantle
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The next Great Alpine Fault Earthquake
Synthetic isoseismals (MM intensity) for a MW 8
earthquake in South Westland (Smith 2002)
?
IX
VIII
X
VII
?
VI
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MM 1 Imperceptible MM 2 Scarcely felt MM 3
Weak MM 4 Largely observed MM 5 Strong MM 6
Slightly damaging MM 7 DamagingGeneral alarm.
People experience difficulty standing. Furniture
and appliances are shifted. Substantial damage to
fragile or unsecured objects. A few weak
buildings are damaged. MM 8 Heavily damaging
Alarm may approach panic. A few buildings are
damaged and some weak buildings are destroyed.
MM 9 Destructive Some buildings are damaged
and many weak buildings are destroyed. MM 10
Very destructive Many buildings are damaged and
most weak buildings are destroyed. MM 11
Devastating Most buildings are damaged and many
buildings are destroyed. MM 12 Completely
devastating All buildings are damaged and most
buildings are destroyed.
The Modified Mercalli (MM) scale
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Effects east of the Alps

• Long-duration (3 4 minutes) low-frequency 1
  Hz) shaking at MM VII - IX

• Closure of alpine passes

• Landslides into lakes - tsunami

• Landslides into rivers landslide dams
  dambreak floods river sedimentation

• Lots of small landslides on hillslopes

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When?

• We are about here
• The further we look into the future, the less
  likely it becomes!
• Why?
• Because it is most likely to occur now!

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But it doesnt have to!

• Probabilities dont tell us when, they just tell
  us how surprised we should be WHEN (not if) it
  happens
• About half of the time it may go more than 400
  years between ruptures
• But the longer it goes without, the bigger it
  gets, and the worse are its consequences

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The Next Great Alpine Fault Earthquake

• Up to 400 km rupture length (Haast Ahaura)
• Up to 8-m horizontal and 4-m vertical
  displacement of trace
• MW 8, so a Great Earthquake not just strong
• Duration minutes not seconds
• Shaking intensity up to MM XII. We will all feel
  it, even in Sydney
• Probability 1 p.a, 15-20 in next 20 years,
  50 in the next 100 years
• Damaging aftershocks up to M 7 for many
  months.

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The Next Great Alpine Fault Earthquake

• Is due to occur
• Is more likely today than tomorrow
• Might not occur for 150 years
• The longer the delay, the bigger it will be
• Will occur with no recognisable warning
• Will have disastrous consequences across many
  regions
• Will cause a sudden-onset national emergency of
  long duration

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The Next Great Alpine Fault Earthquake

• Will alter tectonic stress distribution
• Other faults may rupture in days to decades, or
  rupture on another fault may trigger it
• May rupture along part of its length, with lower
  magnitude but followed shortly by rupture of
  rest
• Two large earthquakes is a realistic scenario
• Anticipate a series of large earthquakes
• There will be large aftershocks anyway

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Geomorphic consequences

• Immediate ground accelerations 1g near fault,
  decreasing with distance, but amplified on ridges
  and peaks
• Less intense shaking in aftershocks (days
  months - years)
• Much ground damage and liquefaction
• Countless landslides - all sizes up to many tens
  of millions of cubic metres from slopes in the MM
  IX areas
• Landslide dams with breakout floods and
  aggradation comparable to and exceeding that
  following 1999 Mt Adams landslide
• High sediment inputs to all rivers lasting for gt
  months.

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There will be many landslides in the mountains

• The landslide from Mount Adams that blocked the
  Poerua River in 1999 is a small taste of what is
  to come.
• The effects downstream will continue for years

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Pourua Valley 2002
River aggradation
Poerua Valley 1988
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Geomorphic consequences

• Landslides in aftershocks for months
• More landslide dams, more flash floods, more
  sediment input, more aggradation, more river
  avulsion and sedimentation
• Debris flows in many small steep catchments in
  heavy rain (1 day 1 year)
• A West Coast tsunami - Okarito? Hokitika?
  Greymouth? Westport? Milford Sound? Doubtful
  Sound? Australia?
• Landslide tsunami - Wakatipu? Wanaka? Hawea? Te
  Anau? Manapouri? Tekapo? Milford Sound? Doubtful
  Sound? Moana? Kaniere?
• Tsunami from delta collapse - Godley? Tasman?
  Rees/Dart? Cleddau? Matukituki? Makarora?

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Geomorphic consequences
Tsunami
Rock avalanche
Dambreak flood
Severe sedimentation
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Societal consequences - immediate
No bridge design performs well in fault rupture
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Societal consequences - immediate

• Transalpine surface routes impassable (weeks)
• Many mountain roads impassable
• Immediate shutdown of all South Island power
  generation and widespread disruption of
  reticulation
• Widespread damage in the MM gt VIII and tsunami
  zones
• Uncontrollable fires
• Widespread disabling injuries medical services
  overwhelmed some deaths

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Societal consequences - immediate

• Land- and cell-phones out in many areas
• Overseas rescue and medical assistance needed
• Severe disruption of all services (water,
  sewerage, energy, communication, transport,
  health, social) (weeks)
• People trapped on roads/tracks or in
  accommodation need to be looked after where they
  are (days - weeks)
• Dairy herds unable to be milked no milk
  transport/processing
• Cessation of most commercial activity in many
  parts of South Island (days - months)
• Many local economies maintained solely by
  recovery (weeks - years)

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Some land transportation routes will be cut
SH6 crosses the Alpine fault many times, and some
bridges are sited on it
Lewis, Arthurs, and Haast Pass routes will be
cut in many places, mostly by landslides and
spreading of road fill
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Not even an earthquake Manawatu, Sept 2011
With concentrated resources, susceptable major
highways can still be out for more than a month
with multiple blockages
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Societal consequences longer term

• Continued disruption of transport and services by
  aftershocks, slope failures, river aggradation
  and flooding (months-years)
• Poor communication, access and lack of fuel
  hamper recovery and redevelopment
• Emergency-management capabilities overwhelmed at
  all levels
• Continued overseas assistance needed in recovery
  (aid, trades people)
• Continued lack of access and fuel on West Coast
  requires assistance from the west (ships and
  aircraft)

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Mitigation What can be done now? National ,
Regional , Community, Family

• FIND OUT ABOUT THE EVENT
• Develop scenarios (worst-case is a useful
  exercise)
• Share your scenarios with other groups. Share
  theirs
• Plan what you will do. Encourage others to do
  likewise
• Find out what your community expects of you and
  tell them what to (not) expect from you

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• Increase awareness of the event among schools,
  local population, businesses, tour operators,
  tourists,
• Dont just talk about it. Do things.
• E.g. All tour buses could carry locators, food,
  drink, blankets, medical supplies (to last
  several days). There will be many buses, many may
  be on the road, their passengers can not all be
  evacuated in a day (week?).
• E.g. Tie down helicopters on the ground
• Identify highest-risk locations and gradually
  strengthen, or redevelop to safer areas

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• Store all essential supplies (fuel, food, spares,
  radios, generators, heavy machinery, medical
  supplies etc) in safe secure locations
• Store Bailey bridges by essential river crossings
• Inventory machinery, helicopters, drivers,
  mechanics, tourists, etc etc and maintain
  electronically and as hard copy available to
  event controllers

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This earthquake is a perfectly normal part of New
Zealands evolution.
Learning to adapt to it is a necessity for
sustainable communities.
It is only one event of many, and many types,
that will occur in NZs future.
Learning to adapt to ALL of them is a necessity
for a sustainable New Zealand
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Electricity reticulation....
... will be crucial following the Alpine fault
earthquake.
SI generation will shut down power will need to
be reticulated from NI.
Will the lines be damaged?

• Tower foundation stability/security?

• Structural integrity of towers in long-duration
  low-frequency shaking (including forces
  transmitted by lines)?

• Lines shorting by swinging?

Where is reticulation controlled from?
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ContactGNS ScienceP.O. Box 30368Lower
Huttm.mcsaveney_at_gns.cri.nzwww.gns.cri.nztim.d
avies_at_canterbury.ac.nzwww.canterbury.ac.nz
University of Canterbury Private Bag
4800 Christchurch