Wish I'd never asked....

[Moorf]

Took the dogs out this morning and, just outside our back gate were a couple of surveyors. Intrigued at their equipment, and what they were doing on our side of the road, I wandered over for a chat.

I wish I hadn't.

They were surveying.... not the road.. ohhh no.... a big quake fault-line that runs, literally, right past our back boundary - they were excited at some "interesting anomalies" that had occured underground right by our back gate

[Sam B]

uh-oh!

[benandclare]

eek

[jubjub]

[Moorf]

Hmmm, there's a hill about 15km up the road from us in Springfield that is on/near the fault line - geologists have found it is rising at 6 inches a year! I posted an article about it last year but it's gone now....

[ourquest]

Moorf, this doesn't add up. Surveyers don't measure or map fault lines, geologists do. And fault lines are often fault zones (ie not entirely confined) and if they described it as an "earthquake fault line" then it might be the result of an earthquake, not the cause of one.

Did they volunteer any information about how they knew what was underground at your back gate?

Usually an active fault can cause earthquakes, but it seems highly unlikely that it would be a new discovery (ie suddenly make your house lie in an area of high risk). New Zealand has so much seismic activity that their will be entire departments monitoring seismographs and interpreting their results on a daily basis.

Unless there are seismic stations all over your garden (there aren't) no scientist would pinpoint underground "activity" to be below your back gate.

Maybe they were enjoying some kiwi humour?

[Moorf]

They were using a ground radar machine-thingy and those tripod thingys and a laptop. Don't ask! Sorry, I didn't mean literally under my back gate - it's rural land out the back and they were all over the place....

They could well have been geologists - they were both Scandanavian so not sure about the Kiwi joke - I just called them surveyors because of the equipment they were using and I pretended to know what they were on about by saying "Oh yes, I love Time Team" *blank looks*....

Not much I can do about it anyway!! Assume it's been there a while

[ourquest]

Your post about the hill appeared before my last response.

If it is moving constantly then it is no risk for earthquake. It is in active fault zones which are under huge tectonic stress without moving where the danger lies. The stress builds up, and when the forces of friction are no longer sufficient, the fault suddenly moves and releases immense energy, which you feel as an earthquake. Geologists cannot predict the occurrence of an earthquake precisely because there is no movement which precedes it. They can only predict which areas carry more risk, and advise construction to be able to withstand the earthquakes. No one has lost a life in NZ as a result of a quake since 1964 (I think), although the risk does exist.

Unless you hear otherwise, assume you are relatively safe. Surveyors might know how to measure position, but neither you nor them have the knowledge to understand the mechanism or risk associated with geological fault zones.

[ourquest]

OK so they might have been geologists. Points still apply.

This is the problem with having an online discussion!

[Moorf]

It could also be part of the big geo-planning that is being done across our area of Canterbury due to the proposal to dam up a huge lake locally (Canterbury Water's great "irrigate the plains" idea. The plans have been opposed as the dam supposedly sits on a fault line, too.

I'll have to go and interrogate them tomorrow!

Well, they do say NZ rocks!