The Alpine Fault Earthquake:
Natural Event and Human
Consequences
Tim Davies
Canterbury University
Mauri McSaveney
GNS Science
Outline
• What’s 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
University of Canterbury
GNS Science
What’s new?
1. The Christchurch earthquakes – what do they tell us?
2. Probabilities don’t help much
3. New Alpine fault information
University of Canterbury
GNS Science
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
University of Canterbury
GNS Science
Probabilities are based on past data and don’t 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...
University of Canterbury
GNS Science
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?
University of Canterbury
GNS Science
Our place on the planet’s 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
Earth’s mantle
University of Canterbury
GNS Science
The next Great Alpine Fault Earthquake
Synthetic isoseismals
(MM intensity) for a MW 8
earthquake in South
Westland (Smith 2002)
?
IX
VIII
X
?
University of Canterbury
VII
Town
HEP
VI
Alpine
pass
GNS Science
MM 1: Imperceptible
MM 2: Scarcely felt
MM 3: Weak
MM 4: Largely observed
MM 5: Strong
MM 6: Slightly damaging
MM 7: Damaging
General 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
University of Canterbury
GNS Science
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
GNS Science
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!
Probablity
0.20%
0.15%
0.10%
0.05%
0.00%
0
500
1000
1500
2000
Rupture interval (years)
University of Canterbury
GNS Science
But it doesn’t have to!
• Probabilities don’t 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
University of Canterbury
GNS Science
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.
University of Canterbury
GNS Science
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
University of Canterbury
GNS Science
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
University of Canterbury
GNS Science
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 > months.
University of Canterbury
GNS Science
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
University of Canterbury
GNS Science
Pourua
Valley 2002
River aggradation
Poerua
Valley 1988
University of Canterbury
GNS Science
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?
University of Canterbury
GNS Science
Geomorphic consequences
Tsunami
Rock avalanche
Dambreak flood
Severe
sedimentation
University of Canterbury
GNS Science
Societal consequences - immediate
No bridge design performs well in fault rupture
University of Canterbury
GNS Science
University of Canterbury
GNS Science
University of Canterbury
GNS Science
University of Canterbury
GNS Science
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 > VIII and tsunami
zones
• Uncontrollable fires
• Widespread disabling injuries; medical services
overwhelmed; some deaths
University of Canterbury
GNS Science
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)
University of Canterbury
GNS Science
Some land transportation routes will be cut
SH6 crosses the Alpine fault many times,
and some bridges are sited on it
Lewis, Arthur’s, and
Haast Pass routes
will be cut in many
places, mostly by
landslides and
spreading of road fill
University of Canterbury
GNS Science
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
University of Canterbury
GNS Science
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)
University of Canterbury
GNS Science
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
University of Canterbury
GNS Science
• Increase awareness of the event among schools,
local population, businesses, tour operators,
tourists, …
• Don’t 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
University of Canterbury
GNS Science
• 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
University of Canterbury
GNS Science
This earthquake is a perfectly normal part
of New Zealand’s 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 NZ’s future.
Learning to adapt to ALL of them
is a necessity for a sustainable
New Zealand
University of Canterbury
GNS Science
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 lowfrequency shaking (including forces transmitted by lines)?
• Lines shorting by swinging?
Where is reticulation controlled from?
University of Canterbury
GNS Science
Contact:
GNS Science
P.O. Box 30368
Lower Hutt
University of Canterbury
Private Bag 4800
Christchurch
m.mcsaveney@gns.cri.nz
www.gns.cri.nz
tim.davies@canterbury.ac.nz
www.canterbury.ac.nz
University of Canterbury
GNS Science