Hawke's Bay Should Be Earthquake Ready

The recent quake in Christchurch centred on a previously un-mapped fault line is a timely reminder for residents of Hawke’s Bay to consider how prepared we are for a major event.

The Central Hawke’s Bay District Council recently published a new set of planning maps to record the latest information from Geological and Nuclear Sciences (GNS) about our fault lines.  The Surveying Company’s director, Brian Foote, says that the new set of planning maps may cause concern to the public because the associated hazard zones are too broad and in some cases would make a property virtually unsaleable.

Council releases advise that the fault lines studied by GNS last year are now called “fault zones” and are shown on the new Planning Maps.  The term “fault zones” is used instead of fault lines because even with the detailed GNS study, there is still uncertainty as to the exact location of faults.

The District Plan says that a fault zone contains a line showing the best estimate of ground rupture or deformation, which is then bounded by a buffer zone reflecting a degree of uncertainty. A better-defined fault results in a narrower fault zone.  In the District Plan, fault zones are defined as either land shown as a fault zone on the planning maps or land within 100 metres of a fault line shown on the planning maps.

However this is not all bad news for Hawke’s Bay residents. The Council intends to use the activity status of a new building to control the design aspects of a new building within a fault zone.  Discretionary activity status will be assigned to any building that is to be constructed within a fault zone that is for daycare or healthcare, designed to hold more than 50 people, any emergency service building, any educational service building designed to hold more than 250 people or any other building designed to hold more than 300 people on a temporary or permanent basis. This on reflection is not too onerous taking into account the Christchurch experience.

The main issue that our company would like to see council respond to is the full supply of information in a LIM report that may be supplied to a potential property purchaser.  If the buyers are given all the facts, they can make an informed choice.  However a brief statement such as “property subject to fault zone” may deter purchasers unnecessarily.

The liquefaction that presented itself in Christchurch could probably happen in the Hawke’s Bay region and when planning your next house site something that should be carefully considered is the location - is it the best and safest possible location for the new building. 

If you would like to discuss your property in more detail give Brian Foote a call. The Surveying Company has an office in Waipukurau and after an initial consultation Brian would be happy to visit your site.  

After the Christchurch earthquake we as surveyors were left wondering how this would affect underlying boundaries.  We have included an excerpt from the Land Information New Zealand website below which gives an insight into how this is dealt with.  These lessons were learnt after the last major Hawke’s Bay earthquake however a lot of time has passed since then and we need to revisit these lessons.

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.