The following questions were posted by a Christchurch resident on our GNS Science Facebook page. I think they are good questions which will be of interest to many people in the quake affected area. I have re- posted them here, along with answers provided by Kelvin Berryman, a leading earthquake scientist at GNS Science, and manager of the Natural Hazards Research Platform. Kelvin was awarded the Queen’s Service Order in the 2011 Queen’s Birthday Honours recently for his services to science.
Request on behalf of everyone who lives in Christchurch, we are all so afraid and re-thinking our futures – it would be good if some questions could be answered in plain English for us:
1. Are you aware of ALL the major fault lines in Canterbury –
Yes I think the research community knows where the MAJOR faults are. However, the current Canterbury earthquakes are being generated by some quite moderate-sized faults – they are buried beneath many 100’s of metres of gravels or the several million year old volcanic rocks of Banks Pensinsula. We cannot see all of this size of fault.
Liquefaction volcanoes dot the beach, June 2011
2. Which faults are the biggest risk for large earthquakes?
The faults that are being strained the hardest have the highest chance of producing large earthquakes. In the South Island these are the Alpine, Hope (through Hanmer to Kaikoura), Porters Pass (look to the right the next time you drive over Porter’s Pass toward the West Coast to see the fault line crossing the hillsides), and further north into Marlborough. Unfortunately all faults that are being strained have to break some time, and this is what is happening around Christchurch at present. These are very rare events for Canterbury, although I realise completely this scientific understanding provides no solace for the people who have lost so much.
Ready to topple… Port Hills boulder
3. What are the future implications, area by area e.g. which are the safest areas to live in?
In Canterbury the safest areas are probably those farthest from current earthquake activity, and to the west away from the liquefaction susceptible areas are better. In New Zealand areas north and west of New Plymouth and Hamilton have a lot fewer earthquakes than other parts of the country. But remember that other natural hazards like floods, and tsunami have different likelihoods in different parts of New Zealand.
4. What % risk is there of a tsunami – I do understand that there are many faults on our coast line, how sure are you that there is no tsunami risk, vertical or horizontal, and why?
Rockfall at Redcliffs RSA
Canterbury does have a risk of tsunami but the principal source is huge earthquakes occurring in South America, and it takes roughly 12 hours for the tsunami to arrive, so there is plenty of time to be safe. The fault lines offshore of Canterbury are small and not capable of producing a major tsunami, but if you are on the beach when you feel a big earthquake and the shaking goes on for 20 seconds or more then it is important to get several metres above the beach. Go quickly walking, perhaps drive if practical, but watch out for being stuck in a traffic jam at low elevation when simply walking or running for 50-100m is all you need to do. If you live near the coast join a local group, obtain readily available information on self evacuation planning, and make a community plan. The local civil defence officer will help you.
5. Are you – (scientists/geologists in Christchurch) afraid when an aftershock hits, if you shared exactly your feelings thoughts on this issue it could give us all some peace on the subject.
To be honest I think the residents of Canterbury have now have more experience of earthquakes than most earthquake scientists. I think most people whether they are scientists or not are apprehensive when an earthquake starts and will often be afraid too. Perhaps we have the advantage of trying to remember our scientific training when in those few seconds we are thinking about how big will it be. I am sure now that with your experience you know that the really big and damaging earthquakes hit so hard that you are thrown down or find it difficult to move. Fortunately these ones are much less common than the smaller but nevertheless worrying ones.
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For more geoscientist’s answers about the Christchurch Earthquakes, have a look at the ‘Ask an Expert’ page published earlier this week in the Christchurch Press.