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)
The Alpine Fault Earthquake:Natural Event and Human Consequences
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…
4. Liquefaction and site effects are a VERY big deal
5. Recovery/rebuilding takes much longer than expected
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...
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?
Earth has a mobile surface divided into “tectonic plates”
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
Synthetic isoseismals (MM intensity) for a MW 8 earthquake in South Westland (Smith 2002)
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
Effects east of the Alps
But it doesn’t have to!
There will be many landslides in the mountains
Pourua Valley 2002
Poerua Valley 1988
Societal consequences - immediate
No bridge design performs well in fault rupture
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
With concentrated resources, susceptable major highways can still be out for more than a month with multiple blockages
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
... 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?
Where is reticulation controlled from?
University of Canterbury
Private Bag 4800