Earthquake risk

The force 7.1 earthquake in Christchurch has inflicted $4 billion worth of damage on the city. Though it was frightening, 7.1 is not especially big. For every whole number increase in the Richter scale the amount of energy released increases by 10. So the Hawke's Bay Earthquake of 1931 was around 4 - 5 times bigger than the one that struck Christchurch. The Boxing day Indian Ocean earthquake off Indonesia that triggered the tsunami was 100 times bigger. That's pretty much as big as earthquakes get.

Looking at the television pictures I am amazed at the lack of reinforcing in so many of the buildings. Just brick plopped on top of brick. Little wonder it all fell down so easily.

Though this particular fault line was unknown, the risk of earthquakes to the city was well known. Just a few tens of kilometers away is the alpine fault, a fracture that extends the entire length of the south island. It is a close relative of faults that also pass through Hawke's Bay.

These fault tines are created by the impact of our planets Pacific plate grinding against the Australasian plate . Here in Hawke's Bay the former is diving under the latter but for much of the South Island the movement is horizontal.

There is clear evidence that at times in the past, hundreds of kilometres of the alpine fault line have moved at the same time. When this happens the result can only be a monumental earthquake of at least force 8 and possibly very much larger.

So to me it is a surprise the city of Christchurch was so ill prepared.

I was personally involved in providing media coverage of the Gisborne shake nearly three years ago and there as well was astonished at how easily so many buildings were seriously damaged. Christchurch now seems very like Gisborne was then though on a very much larger scale.

Hawke's Bay had its own disaster in 1931 but had also been warned only a couple of years earlier by a large earthquake centered somewhere close to Porangahau. Incredibly in the same area as our own recent rash of quakes, including a 5.3 shake.

Some took heed of the danger and most notable of these was the Public Trust Office. We have all seen pictures of their Napier edifice standing intact against a background of total destruction.

Woodford House school was also alarmed by the inadequacy of their architecture and demolished a near new classroom block to replace it with a seismic sound structure. This decision may have saved the school from being put out of business.

Since most of Napier and the most vulnerable structures in Hastings fell down the bulk of our older buildings are made from ferro concrete.

So where does Hawke's Bay stand today. My guess is most houses will survive a major shake mainly because they are built from wood. Likewise I feel most commercial buildings will still be standing or at least will stand up for long enough for everybody to get out unharmed.

The biggest danger I see are the other affects of ground shaking. Clearly liquefaction, or the way waterlogged sandy or alluvial soil takes on the properties of a liquid when shaken could be a problem. Probably more so in Napier than Hastings because the water table is often just below the surface, as evidenced by the many pumping stations around the city.

Under severe shaking structures could simply sink into the ground or could even be swallowed up completely.

For me the biggest risk is tsunami. Any great movement on the seabed would cause massive displacement of the sea and this could easily turn into a wall of water racing several metres deep across what we now think of as dry land.

Its even possible the land gained from the sea could be returned to the sea if the ground level drops.

So are we prepared. Well I think not. I have watched how we handle much smaller events such as the serious flooding around Tamatea a few years ago, and more importantly the South American tsunami earlier this year.

For a start we have an organisational problem. All three councils run their own civil defence operations. There seems to be nothing binding them together, and judging by their handling of the tsunami there seems to be total inconsistency on how to handle an emergency.

If a wall of water meters deep heads to the city how are the authorities going to get everyone out of the way. How are those without transport or mobility going to be saved? What are the chances of roads being impassable?

All roads out of the city need to be made one way instantly, and there must be a plan to open paddocks for car parking so the roads do not block up and become impassable. We may have as little as 10 minutes of opportunity to save people after which it could be too late.

Few of us have ever been involved in a real emergency rescues. If there is a plan who knows of it? What manpower will be available?

The only people I have any confidence in is fire and ambulance services who are used to dealing with emergencies. Unfortunately I am not convinced the police will make any great contribution. Even beyond the initial impact army and others from outside may struggle to get here.

Chances are the airport will be closed though perhaps Bridge Pa might be operational, however do they have generators to operate the runway lighting. One area where we do seem well endowed is helicopters but is there a plan to coop their services?

We don't want to become paranoid but my concern is , there is no plan, and no one capable of making a huge difference in an emergency situation.