Christchurch earthquakes

**FJRider** · 14th June 2011, 19:20

Originally Posted by oneofsix

Re-establishing the correct placement of the pegs could take a shit load of work because first someone has to prove the base reference marks, trig stations generally, haven't moved or re-establish their true positions before they can check the next tier and so on down to the boundary pegs.

GPS will save a shit-load of time ...eh ...

**Oakie** · 14th June 2011, 20:34

Originally Posted by FJRider

GPS will save a shit-load of time ...eh ...

Unfortunately the original locations weren't recorded by GPS ... but I guess you knew that.

**FJRider** · 14th June 2011, 20:41

Originally Posted by Oakie

Unfortunately the original locations weren't recorded by GPS ... but I guess you knew that.

They can go off the points that WERE ....

**Oakie** · 14th June 2011, 20:43

Originally Posted by FJRider

They can go off the points that WERE ....

...but they don't have a reference for where the points were.

**oneofsix** · 14th June 2011, 20:59

Originally Posted by Oakie

Unfortunately the original locations weren't recorded by GPS ... but I guess you knew that.

GPs wasn't an option way back last century when I played with surveying but I suspect it isn't accurate enough anyhow. 1 metre resolution certainly wouldn't do it

**oneofsix** · 14th June 2011, 21:04

Originally Posted by Oakie

...but they don't have a reference for where the points were.

That's part of the problem I guess. But each trig is referenced back to at least two others. Work from far enough out you can reestablish your datums but it would take time and effort. I stand to be corrected by someone who actually does this stuff.

**jim.cox** · 14th June 2011, 21:40

Originally Posted by oneofsix

That's part of the problem I guess. But each trig is referenced back to at least two others. Work from far enough out you can reestablish your datums but it would take time and effort. I stand to be corrected by someone who actually does this stuff.

Well I USED to do this stuff

And there is no denying that the Chch quakes have given the surveyors a whole lot to do

But in general, the boundary peg marks the boundary. When the peg moves by natural means, and the movement is over a large area, then the boundary moves also. If your place moves, and the neighbours moves, so will the boundary

There are exceptions to this rule - and it certainally doesn't cover deliberate movement by person or persons known or unknown.

The bigger problem comes when the boundary peg is not there - how do you know where it should be?

A GPS can be useful, but the survey system in NZ does not rely on the absolute coordinates - there is too much measurable movement (even without earthquakes) for that. Its the relative positions of the pegs, survey marks and trig stations that count.

Some of the the measurements taken since September last year show that the Port Hills have risen by about 470mm - and some of the side ways movements are five to six metres

**oldrider** · 15th June 2011, 14:53

Strange things are going on and when you take in to consideration how Zealandia was driven up from beneath the sea, it is not surprising!

I worry that Christchurch is not simply a dress rehearsal for some even more significant event!

Apparently a periodically measurable movement on the main fault line is quite long overdue!

**jim.cox** · 15th June 2011, 15:00

Originally Posted by oldrider

Strange things are going on and when you take in to consideration how Zealandia was driven up from beneath the sea, it is not surprising!

I worry that Christchurch is not simply a dress rehearsal for some even more significant event!

Apparently a periodically measurable movement on the main fault line is quite long overdue!

Take a look at these images grabbed from geonet.org.nz

Do you see a pattern ?

**oneofsix** · 15th June 2011, 15:01

Originally Posted by jim.cox

Well I USED to do this stuff

And there is no denying that the Chch quakes have given the surveyors a whole lot to do

But in general, the boundary peg marks the boundary. When the peg moves by natural means, and the movement is over a large area, then the boundary moves also. If your place moves, and the neighbours moves, so will the boundary

There are exceptions to this rule - and it certainally doesn't cover deliberate movement by person or persons known or unknown.

The bigger problem comes when the boundary peg is not there - how do you know where it should be?

A GPS can be useful, but the survey system in NZ does not rely on the absolute coordinates - there is too much measurable movement (even without earthquakes) for that. Its the relative positions of the pegs, survey marks and trig stations that count.

Some of the the measurements taken since September last year show that the Port Hills have risen by about 470mm - and some of the side ways movements are five to six metres

thanks, so no risk of a house being rebuilt in the same place but now spanning a boundary line.

**mashman** · 15th June 2011, 15:05

Originally Posted by jim.cox

Take a look at these images grabbed from geonet.org.nz

Do you see a pattern ?

Doesn't Iceland do a similar thing... albeit a little more dramatically.

**oneofsix** · 15th June 2011, 15:12

Originally Posted by jim.cox

Take a look at these images grabbed from geonet.org.nz

Do you see a pattern ?

theere was the forgotten big quake in Fjordland, on the pacific plate I believe. Then Christchurch on the Australian plate, a bit like a stress transfer and push it a bit north. If you go further north and back to the pacific plate?

**slofox** · 15th June 2011, 15:29

Originally Posted by oldrider

I worry that Christchurch is not simply a dress rehearsal for some even more significant event!

Yes. So do I. Been wondering about that for a couple of days now.

**YellowDog** · 15th June 2011, 16:18

http://www.nzherald.co.nz/nz/news/ar...732407&ref=rss

Christchurch police are again warning that people may be passing themselves off as officials so they can steal in the wake of Monday's earthquakes.

No significant earthquake-related crime had been reported since the quakes and the nights had been quiet, but police did get one or two calls about people wearing high visibility vests and possibly passing themselves off as earthquake response workers, said Canterbury police district commander, Superintendent Dave Cliff.

"A high viz vest is no guarantee of authenticity and we encourage people to ask for identification."

People were urged to report suspicious behaviour - anyone who looks out of place, or unknown vehicles and people cruising around streets - to police.

After the deadly February 22 quake Christchurch saw a spike in burglaries and a number of people trying to pass themselves off as EQC staff, wearing high-visibility vests, going door-to-door and asking people about their electronic equipment.

- NZPA