The Alpine Fault Earthquake : Natural Event and Human Consequences

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

2. 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

3. What’s new? 1. The Christchurch earthquakes – what do they tell us? 2. Probabilities don’t help much 3. New Alpine fault information

4. 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

5. 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...

6. 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?

7. 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

8. 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 ?

9. 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

10. 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

11. 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!

12. 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

13. 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.

14. 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

15. 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

16. 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.

17. 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

18. Pourua Valley 2002 River aggradation Poerua Valley 1988

19. 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?

20. Geomorphic consequences Tsunami Rock avalanche Dambreak flood Severe sedimentation

21. Societal consequences - immediate No bridge design performs well in fault rupture

25. 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

26. 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)

27. 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

28. 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

29. 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)

30. 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

31. 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

32. 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

33. 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

34. 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?

35. Contact:GNS ScienceP.O. Box 30368Lower Huttm.mcsaveney@gns.cri.nzwww.gns.cri.nztim.davies@canterbury.ac.nzwww.canterbury.ac.nz University of Canterbury Private Bag 4800 Christchurch