The alpine fault earthquake natural event and human consequences
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The Alpine Fault Earthquake : Natural Event and Human Consequences. UPDATE. 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)

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The Alpine Fault Earthquake : Natural Event and Human Consequences

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The alpine fault earthquake natural event and human consequences

The Alpine Fault Earthquake:Natural Event and Human Consequences

UPDATE

Tim Davies

Canterbury University

Mauri McSaveney

GNS Science


Outline

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


The alpine fault earthquake natural event and human consequences

What’s new?

1. The Christchurch earthquakes – what do they tell us?

2. Probabilities don’t help much

3. New Alpine fault information


The alpine fault earthquake natural event and human consequences

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


The alpine fault earthquake natural event and human consequences

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...


The alpine fault earthquake natural event and human consequences

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?


Our place on the planet s scheme of things

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


The next great alpine fault earthquake

Town

HEP

Alpine pass

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

?


The alpine fault earthquake natural event and human consequences

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


The alpine fault earthquake natural event and human consequences

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


The alpine fault earthquake natural event and human consequences

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!


The alpine fault earthquake natural event and human consequences

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


The next great alpine fault earthquake1

The Next Great Alpine Fault Earthquake

  • Up to 400 km rupture length (Haast – Ahaura)

  • Up to 8-m horizontal and 4-m vertical displacementof 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.


The next great alpine fault earthquake2

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


The next great alpine fault earthquake3

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


Geomorphic consequences

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.


The alpine fault earthquake natural event and human consequences

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


The alpine fault earthquake natural event and human consequences

Pourua Valley 2002

River aggradation

Poerua Valley 1988


Geomorphic consequences1

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?


Geomorphic consequences2

Geomorphic consequences

Tsunami

Rock avalanche

Dambreak flood

Severe sedimentation


The alpine fault earthquake natural event and human consequences

Societal consequences - immediate

No bridge design performs well in fault rupture


Societal consequences immediate

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


Societal consequences immediate1

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)


The alpine fault earthquake natural event and human consequences

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


Not even an earthquake manawatu sept 2011

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


Societal consequences longer term

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)


Mitigation what can be done now national regional community family

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


The alpine fault earthquake natural event and human consequences

  • 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


The alpine fault earthquake natural event and human consequences

  • 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


The alpine fault earthquake natural event and human consequences

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


The alpine fault earthquake natural event and human consequences

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?


The alpine fault earthquake natural event and human consequences

Contact:GNS ScienceP.O. Box 30368Lower [email protected]@canterbury.ac.nzwww.canterbury.ac.nz

University of Canterbury

Private Bag 4800

Christchurch


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