Canterbury Earthquake Q&As

New questions and answers, along with additional technical information, will be posted on this site as the information becomes available.

Further information for Canterbury surveyors is available. Technical queries or comments can be sent to darfieldearthquake@linz.govt.nz.

All media enquiries should be directed to media@linz.govt.nz.

Cadastral Surveying

• Surveyors will need to collect appropriate field evidence before raising specific questions on individual cadastral surveys.
• Please ensure that you correctly populate the Landonline ‘survey finish date’ field with the date the field work was completed.

I have completed all field work for a job in Canterbury prior to 4 September 2010. Can I still lodge the dataset?

Yes, but ensure that the Landonline field ‘survey finish date’ reflects the date field work was completed. Also confirm in your survey report that the survey field work was completed prior to 4 September 2010. Your dataset will then be processed as any dataset lodged before 4 September 2010.

My dataset, lodged before 4 September, has been requisitioned and requires additional field work – how do I proceed with the field work?

It is important that the new field work can be demonstrated to be in terms of the original work you completed for this survey.

The Surveyor-General dispensation process can be used, where appropriate, to address Rules compliance issues. Additional advice will also be provided on a case by case basis.

Most of the field work was completed before 4 September but there are still one or two pegs to be placed – what do I do?

It is important that the new field work on uncompleted jobs can be demonstrated to be in terms of the original work you undertook.

The current Surveyor-General dispensation process may be used, and additional advice provided where appropriate, to resolve Rules compliance issues on a case by case basis.

I started my survey before the earthquake but still have a lot of field work to complete. Will I have to re-survey my original work?

All field work in the survey will have to reflect the situation at the date of ‘survey completion date’. You will have to assess the reliability of your original field work, and undertake any re-surveying as necessary, before progressing the job.

Where do I start - what are the key requirements for new surveys in the area affected by the earthquake?

You will need to establish a reliable orientation independent of marks disturbed by the earthquake. Care will need to be taken when using existing base stations and geodetic control marks as your previous understanding of bearing corrections will need to be reconfirmed.

Boundary definition, including recalculations, will need to take into account any movement or distortion due to the earthquake. You will therefore need to demonstrate connections to close marks & occupation and address any issues.

What effect does land movement caused by the earthquake have on property boundaries?

Where land has moved as a result of the earthquake in most cases the boundaries will have moved by a corresponding amount. While the small number of properties bisected by the fault trace may need more careful consideration by surveyors, the great majority of property boundaries are not materially affected.

If a fence or wall was on the boundary before the earthquake, it is reasonable to assume that it is still on the boundary afterwards. Therefore wholesale re-survey of boundaries should not be required. Landowners rebuilding fences or buildings that are close to the boundary will often need to get a surveyor in to confirm the position of the boundary - but this is usually a good idea anyway.

The positions of boundaries are based on physical evidence in the ground - mainly survey marks, including boundary pegs. Surveyors re-establishing boundaries also consider other evidence, where relevant, such as the relationship of fences and buildings to the boundary.

As was found after the 1987 Edgecumbe earthquake, the best solutions for re-establishing boundaries are based on evidence, common law and common-sense with little need for intervention by the Courts to resolve boundary issues.

What are the orientation requirements for post earthquake surveys?

Where GNSS (Global Navigation Satellite System) positioning is available this will provide the most reliable orientation independent of the effects of the earthquake.

Where GNSS is not available orientation can be based on local control marks (where available), or cadastral marks, which are consistent relative to each other.

It is envisaged that this will apply in areas where there has been relatively uniform movement as a result of the earthquake. Until the re-survey of the control network has been completed, which could take several months, the exact extent of the movement, or the effect on orientation, will be unknown In the meantime the orientation can be in terms of pre-earthquake data and can be deemed to be in terms of the applicable official geodetic projection. The plan should be annotated "Orientation is in terms of pre-Canterbury earthquake 2010 data and may not be accurate relative to the official geodetic projection".

Following completion of the control network re-survey, the Landonline coordinates for post earthquake cadastral surveys can be re-adjusted, and orientation corrections determined, if necessary. It is anticipated that this would not be the responsibility of the original submitting surveyor but would be completed either by LINZ or subsequent surveys.

Where a fault line or local distortions make it difficult to determine a reliable orientation this will need to be resolved on a case by case basis. If necessary consult LINZ (email darfieldearthquake@linz.govt.nz) with details of a proposed solution. Where appropriate a dispensation could be granted.

As usual the basis for determining orientation should be fully covered in the survey report (Rule 8.2(a)(ii)) including any consistency issues.

We would appreciate specific examples of post earthquake survey issues which will assist with developing, or modifying, appropriate responses.

Geodetic System

What is LINZ doing to re-establish survey control?

The proposed timeline for the re-establishment of geodetic control in the earthquake-affected parts of Canterbury is given in the table below. These dates are approximate only and final dates will depend on the extent of post-seismic displacement and results of initial surveys.

Activity	Approximate Timeframe
GNS deformation survey 1 (a survey of order 2 and 3 marks closest to the fault line)	6-10 September
Analysis of results of GNS deformation survey 1	13-17 September
Planning Regional control survey (a survey of order 1-4 marks outside the fault zone)	20 September - 1 October
GNS deformation survey 2 (a survey of order 2 and 3 marks closest to the fault line)	27 September - 1 October
Regional control survey (a survey, to order 4 standards, of all order 1-4 marks outside the fault zone)	October
Analysis of Regional control survey	Early November
Planning Local deformation survey (an order 5 survey in areas of localised deformation, using coordinates from the Regional deformation survey for control)	November
Local deformation survey	December - February 2011
Fault zone control survey (a survey of order 2-5 marks close to the fault line)	January - February 2011
Landonline and Geodetic Database coordinate update	April 2011

When will LINZ update the geodetic control coordinates in Landonline?

Once all control surveys are complete (see question 'What is LINZ doing to re-establish survey control?'), coordinates will be updated in Landonline and the Geodetic Database. We will then readjust the cadastre in terms of the new control. This is expected to take place in about April 2011.

Updating all coordinates at once will reduce inconsistencies in post-earthquake datasets collected at the same time. If control were updated progressively, some datasets would be using post-earthquake control and some would be using pre-earthquake control.

What geodetic information is currently available?

View the plot of post-earthquake movements in Christchurch below, as at November 2010.

How is LINZ going to distinguish between pre- and post-earthquake positions?

In many instances we expect the control marks to have moved consistently with the other survey marks so the relationships between them will not have changed. Therefore where possible the coordinates of all marks will be consistently moved to their "new" positions. Where new coordinates are assigned to control (orders 0 to 5) and cadastral marks, the date of their computation will be indicated - via the geodetic database for control marks. The pre-earthquake values will also be available for every coordinate that is updated. Since both coordinates will be available for each mark it should be unnecessary to create a duplicate mark with a "No 2" name.

Where there has been significant localised deformation it is likely that the control marks and many survey marks will have moved inconsistently, and in many cases will have been destroyed by restoration works. We will need to evaluate each of these cases on its own merits, however it is probable that if such random deformation has occurred the control marks will be noted as disturbed and re-surveyed. In some cases, new marks with new names may be established. Where possible, these will be connected to the existing (disturbed) marks.

How can surveyors assist with the re-establishment of the survey control system?

To obtain the most accurate analysis of deformation, it is desirable to have accurate survey data on marks shortly before the earthquake. This is then compared with data gathered in the re-survey to estimate the movement of that mark.

In the Canterbury region, most order 4 and better control marks have not been resurveyed by LINZ or GNS Science since the initial implementation of NZGD2000 in the late 1990s.

Therefore, LINZ is requesting data from any agencies or companies that have occupied any order 4 or better mark that is within 100km of Darfield.

Data should have the following characteristics:

• at least one hour of GPS/GNSS data collected
• antenna heights accurately measured
• complete metadata for the setup available (eg antenna type, antenna reference point)
• dual-frequency carrier phase data logged (ie survey-quality data)
• collected in the past 2 years

View survey marks of interest - red symbols denote high priority marks within 50km of the earthquake and blue indicate lower priority marks that are also of interest to us.

Preferably the data should be in RINEX format, but other proprietary formats will be accepted. Anyone who thinks they may have suitable data is requested to contact Nic Donnelly at ndonnelly@linz.govt.nz.

How can I use control in the affected area?

Geodetic control may have been impacted by the earthquake and resultant localised deformation.

For surveys covering a large area, or including the fault rupture or other localised deformation, the movements caused by the earthquake are unlikely to be uniform across the survey. It is recommended that reliable local control marks are well-distributed through the survey.

For example, where surveys use a distant GNSS base station, reliable local control should be included in the survey to ensure that the survey is terms of the local area.
 

What is the impact on cadastral coordinates?

Initial estimates of displacements indicate that many of the SDC coordinates in the Christchurch area will no longer comply with network accuracy (absolute accuracy) standards. Once geodetic control has been updated, these coordinates will also be updated to reflect the post-earthquake physical location of the point. In the meantime, there are no plans to remove SDC-status or change the order of these points.

For many surveys, which take place over a small, localised area, the coordinates will probably still be in terms of each other and local geodetic survey control. Again, it is important to tie to and prove the reliability of local control marks, and not rely solely on distant connections to base stations.