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10.5 puts myth and fantasy ahead of facts - 03/06/2004

A mini-series screening on TV2 this weekend about a massive earthquake on the west coast of the United States contains a number of exaggerations and fallacies.

10.5 is a fantasy disaster movie and while such epics can be great entertainment, they are often at odds with the real world.

The producers of 10.5 concede that the movie uses dramatic license when it comes to the science of earthquakes. But they say it was never intended to be factual.

Big earthquakes, like what is depicted in 10.5, are naturally occurring events well outside the powers of humans to create or stop.

The biggest earthquake in New Zealand since European settlement was the 1855 magnitude 8.2 quake in Wairarapa. This is an impressively large quake in global terms. Because New Zealand was sparsely populated at the time, damage was minor.

If there is one takeaway message from the 10.5 mini-series, it is that New Zealanders should be prepared for a damaging earthquake. About 1 percent of the 16,000 earthquakes recorded in New Zealand each year are big enough to be felt by humans.

New Zealand can expect a magnitude 7 earthquake about once every decade and a magnitude 8 once every century. But a magnitude 10.5 is highly unlikely.

The largest quake ever recorded was a magnitude 9.5 on 22 May 1960 in Chile. It occurred on a fault almost 1600km long.

A magnitude 10.5 quake would need a fault much longer than 1600km. However, no such mega-fault is known to exist.

One factual part of the mini-series is the phenomenon of hidden fault lines, sometimes called blind thrust faults. They have very little expression at the surface and are therefore difficult to detect. It is possible they are common in New Zealand, although only a handful have been identified.

The 1931 magnitude 7.8 Hawke's Bay earthquake is a classic example of a blind thrust fault rupturing and causing devastation over a wide area. It is not feasible, as the mini-series suggests, that nuclear explosions and other human activities can start or stop earthquakes.

Scientists have concluded that even large nuclear explosions have little effect on earthquakes outside the immediate area of the blast. And deep mining has been known to cause small to moderate quakes in the immediate vicinity of the mine. But not large, or distant earthquakes.

Another common fallacy is that two earthquakes occurring on the same day must be related even though their epicentres are thousands of kilometres apart. Over long distances, the earth's rocky crust is not rigid enough to transfer stress efficiently.

It is also fiction to suggest that large earthquakes can be stopped by making lots of small ones or by lubricating the fault with water. There can never be enough small earthquakes to completely eliminate large quakes. And injecting high-pressure fluids into the ground is known to be able to trigger earthquakes, rather than stop them.

Another fiction is that it is not possible to plan ahead for an earthquake. On the contrary, there is a huge amount that can be done to minimise the impact of earthquakes and other natural disasters. For more information visit the Ministry of Civil Defence and Emergency Management website:

For information on quake-safing your home and about natural disaster insurance cover provided by the Earthquake Commission go here: http://www.eqc.govt.nz