alpine fault 2011

8/13/2019 Alpine Fault 2011

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The Alpine Fault Earthquake:

Natural Event and Human

Consequences

Mauri McSaveney

GNS Science

Tim Davies

Canterbury University


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GNS ScienceUniversity of Canterbury

Outline

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

Whats new?


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Whats new?

1. The Christchurch earthquakeswhat 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 happenthe Alpine fault WILL rupture,

so will the Wellington fault

2. The Chch earthquakes were smallwe are VERY

vulnerable. The Alpine fault will be ~ 60 x more energetic

3. Most big earthquakes occur on previously unknown

faultsbut the Alpine and Wellington faults will be

exceptions

5. Recovery/rebuilding takes much longer than expected

4. Liquefaction and site effects are a VERY big deal


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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.

Things may be worse than we think...

The Japan earthquake of 11 March was M = 9.0; the

expected magnitude was 8.5


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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 Mw8.2 instead of 8...

However: it appears likely that the rupture will not

initiate in the south and propagate northwardsgood

news?


7/35GNS ScienceUniversity of Canterbury

Our place on the planets scheme of thingsEarth has a mobile surface divided into tectonic plates

The

New Zealandcont inent

is on one of the

plate boundaries

The Alpine fault

connects two

subduction

margins whereocean floor

descends into the

Earths mantle



?

?

VII

VIII

IX

X

The next Great Alpine Fault Earthquake

VI

Synthetic isoseismals

(MM intensity) for a MW8

earthquake in South

Westland (Smith 2002)

Town

HEP

Alpine

pass



MM 1: Imperceptible

MM 2: Scarcely felt

MM 3: Weak

MM 4: Largely observed

MM 5: Strong

MM 6: Slightly damagingMM 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 aredestroyed.

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: DevastatingMost 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 (34 minutes) low-frequency ~ 1 Hz)

shaking at MM VII - IX

Closure of alpine passes

Landslides into lakes - tsunami

Landslides into riverslandslide dams; dambreak floods;

river sedimentation

Lots of small landslides on hillslopes



When?

0.00%

0.05%

0.10%

0.15%

0.20%

0 500 1000 1500 2000

Rupture interval (years)

Probablity

We are about here

The further we look

into the future, the

less likely itbecomes!

Why?

Because it is most

likely to occur now!



But it doesnt have to!

Probabilities dont tell us when, they just tellus how surprised we should be WHEN(not if)it happens

About half of the time it may go more than400 years between ruptures

But the longer it goes without, the bigger itgets, and the worse are its consequences



Up to 400 km rupture length (HaastAhaura)

Up to 8-m horizontal and 4-m vertical displacement of trace

MW~ 8+, so a Great Earthquakenot just strong

Duration minutes not seconds

Shaking intensity up to MM XII. We will all feel it, even inSydney

Probability ~1% p.a, 15-20% in next 20 years, ~50% in thenext 100 years

Damaging aftershocks up to M = 7+ for many months.

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





Will alter tectonic stress distribution

Other faults may rupture in days to decades, orrupture on another fault may trigger it

May rupture along part of its length, with lowermagnitude; 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

Immediate ground accelerations ~1g near fault, decreasingwith distance, but amplified on ridges and peaks

Less intense shaking in aftershocks (daysmonths - years)

Much ground damage and liquefaction

Countless landslides - all sizes up to many tens of millions ofcubic metres from slopes in the MM IX areas

Landslide dams with breakout floods and aggradation

comparable to and exceeding that following 1999 Mt Adamslandslide

High sediment inputs to all rivers lasting for > months.



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 tocome.

The effects downstream

will continue for years

P Ri d ti



Poerua

Valley 1988

Pourua

Valley 2002

River aggradation



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 (1day1 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?

eomorp c consequences



Tsunami

Rock avalanche

Dambreak flood

Severe

sedimentation

eomorp c consequences



No bridge design performs well in fault rupture

Societal consequences - immediate


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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 tsunamizones

Uncontrollable fires

Widespread disabling injuries; medical servicesoverwhelmed; some deaths


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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 belooked 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 SouthIsland (days - months)

Many local economies maintained solely by recovery (weeks -years)


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Some land transportation routes will be cut

Lewis, Arthurs, andHaast Pass routeswill be cut in manyplaces, mostly by

landslides andspreading of road fill

SH6 crosses the Alpine fault many times,and some bridges are sited on it


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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 consequenceslonger 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 recoveryand redevelopment

Emergency-management capabilities overwhelmed at all levels

Continued overseas assistance needed in recovery (aid, tradespeople)

Continued lack of access and fuel on West Coast requiresassistance 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. Sharetheirs

Plan what you will do. Encourage others to do

likewise

Find out what your community expects of you andtell 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 graduallystrengthen, or redevelop to safer areas


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Store all essential supplies (fuel, food, spares,radios, generators, heavy machinery, medicalsupplies etc) in safe secure locations

Store Bailey bridges by essential river crossings

Inventory machinery, helicopters, drivers,mechanics, tourists, etc etc and maintainelectronically and as hard copy available to event

controllers


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This earthquake is a perfectly normal partof New Zealands evolution.

Learning to adapt to it is a necessity forsustainable communities.

It is only one event of many, and manytypes, that will occur in NZs future.

Learning to adapt to ALL of themis 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 downpower will need to bereticulated 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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Contact:

GNS ScienceP.O. Box 30368

Lower Hutt

[email protected]

www.gns.cri.nz

[email protected]

www.canterbury.ac.nz

University of Canterbury

Private Bag 4800

Christchurch

alpine fault 2011

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