The Alpine Fault Earthquake: Natural Event and Human Consequences Mauri McSaveney GNS Science Tim Davies Canterbury University UPDATE

The Alpine Fault Earthquake:

Natural Event and Human Consequences

Mauri McSaveney

GNS ScienceTim Davies

Canterbury UniversityUPDATE

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

• What’s new?


What’s new?

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

2. Probabilities don’t help much

3. New Alpine fault information


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…

5. Recovery/rebuilding takes much longer than expected

4. Liquefaction and site effects are a VERY big deal


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.

Things may be worse than we think...

The Japan earthquake of 11 March was M = 9.0; the expected magnitude was 8.5


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 thingsEarth has a mobile surface divided into “tectonic plates”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


?

?

VII

VIII

IX

X

The next Great Alpine Fault Earthquake

VI

Synthetic isoseismals (MM intensity) for a MW 8 earthquake in South Westland (Smith 2002)

TownHEP

Alpine pass


MM 1: Imperceptible MM 2: Scarcely feltMM 3: WeakMM 4: Largely observedMM 5: StrongMM 6: Slightly damagingMM 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

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


When?

0.00%

0.05%

0.10%

0.15%

0.20%

0 500 1000 1500 2000

Rupture interval (years)

Pro

ba

blit

y

• 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!


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


• 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.

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, 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

• 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.


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


Poerua Valley 1988

Pourua Valley 2002

River aggradation



• 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?


Tsunami

Rock avalanche

Dambreak flood

Severe sedimentation



No bridge design performs well in fault rupture

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



• 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)


Some land transportation routes will be cut

Lewis, Arthur’s, and Haast Pass routes will be cut in many places, mostly by landslides and spreading of road fill

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

itit


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

• 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

• 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


• 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


• 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


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


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?


Contact:

GNS ScienceP.O. Box 30368Lower Hutt

[email protected]

[email protected]

University of Canterbury Private Bag 4800Christchurch

Documents

The Alpine Fault Earthquake: Natural Event and Human Consequences Mauri McSaveney GNS Science Tim Davies Canterbury University UPDATE