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Lessons learned from the earthquakes

2011 has certainly been a year of learning.  Here in Christchurch we have certainly learnt a lot about earthquakes, the terminology and some of the science behind them.

At Fox & Associates we have had the opportunity to be involved with a huge variety of earthquake related work and this has required us to think outside the square about the method of collection but also delivery of the data.

Michael has talked about visualisation of data and how we have had to adapt our process but we have also learnt a thing or two about the collection of data.  We have some very clever people here who would describe themselves as measurement specialists but as always there is usually a project that is so different from any other that we need to adapt our solutions.

This adaption has involved using a variety of non-traditional (for Fox) survey equipment and applying the technology in such a way so as to deal with the physical limitations of the site.

It would be fair to say that we have enjoyed the challenge of the projects though not the sad topic of the projects.

If we had to summarise in one word the fundamental challenge of the earthquake related surveys it would be – stability.

On a macro level we need absolute stability of control marks so that when we are monitoring we have the ability to compare data and calculate the changes.  If we solely rely on local positions we do not know the global changes, if there are differential changes which marks have shifted and which haven’t whether it be a straight translation or is it a rotation?

To resolve this issue we extensively used GPS (iBase and VRS) and post processed the data to relate the control to stable/reliable positions.  In this case we used National Survey Control Marks 87km away at Lake Taylor.  These marks are outside of the area of influence of the Canterbury Earthquakes and we also have continuous access to observation data.

On a micro level we need situational stability for the observation equipment.  Many times vibrations from demolition or nearby equipment caused severe enough vibrations that we were unable to take observations let alone precise observations.  This has involved us isolating the equipment from the vibration or more often than not working outside the normal hours of operation so thank you to all our staff who have assisted with this process.

I am proud of the service and results that we have been able to provide and we have received many positive comments from engineers and clients in respect of the information supplied.

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