A Near Tsunami

But what about a Near Tsunami – one caused by (say) an earthquake in the offshore faults under Pegasus Bay?

The first point is there has not been one in our recorded history, so we know very little about possible effects. But three good assumptions can be made from other Near Tsunami, such as the one which hit New Guinea in 1998. Firstly, it will be relatively soon after the quake – minutes, not hours. Secondly, it will be high enough to overtop any reasonable seawall, dune or other coastal defence. Thirdly, it will be energetic enough to go a fair distance inland. In the 1998 New Guinea quake, for example, a 10+ metre high wave washed a village on a spit into the lagoon beyond, crossed the lagoon, and carried on for 1.3 km into the coastal mangrove forest beyond. Details are at NOAA

A good place to start is to model the effects of a Near Tsunami: New Scientist (Issue 2482 P 16) notes that the Pacific Marine Environmental Lab in Seattle has software which has accurately replicated the Boxing Day tsunami in the Indian Ocean. Policy suggestion is straightforward:

Fund the modeling of a Near Tsunami caused by a Pegasus Bay fault rupture

There is absolutely no way to plan a conventional Civil Defence evacuation for a Near Tsunami. The wave run time is just too short – minutes, probably. And it cannot be assumed that any Avon bridges would actually remain usable. There is concern over all the Avon bridges’ ability to withstand a large, local earthquake - the working assumption has to be that these bridges are unusable.

And as Guy Fawkes night regularly demonstrates to us all, even if those bridges are open, getting out of Brighton fast enough to outrun a Near Tsunami is really not a viable option.

This means that we have to look to our immediate environment for help – within the distance we could run in say 10 minutes.

In Japan, which sits on the junction of three highly active tectonic plates, some coastal cities maintain a series of what are termed ‘tsunami towers’ to which locals can escape. As ‘New Scientist’ (Issue 2482 p 13) notes, these are reinforced structures, and locals are trained to ‘run for the tower’ immediately a large local quake is detected.

So, if we had a tower to run to, our best bet is to ‘run for the tower’.