Submission to the Parliamentary Commissioner for the Environment regarding problems with the Resource Management Act relating to earthquake hazards, especially active faults
Because of New Zealand‚s position on an active plate boundary, most parts of the country are likely to suffer damaging shaking from earthquakes within a human lifetime. The Geological Society of New Zealand is concerned to ensure that scientific knowledge on known or likely earthquake hazards is systematically applied throughout the country to minimise injury and loss of life as well as damage to property.
Within New Zealand, the Resource Management Act (1991 and amendments) gives both regional and local authorities the responsibility of controlling land-use "for the avoidance and mitigation of natural hazards". Unfortunately there are no national standards or policies for the identification or mitigation of natural hazards, and after almost a decade of the RMA it is becoming clear that there is considerable variation in the way that individual councils have approached their responsibilities. For example, few councils identify known active faults within their district plans, let alone having stated policies on building on or near an active fault (Becker & Johnston 2000). Earthquake information and mitigation measures on district plans often varies between adjacent councils, even where they share the same hazard.
HAZARDS ASSOCIATED WITH ACTIVE FAULTS
In addition to widespread shaking, hazards from earthquakes may produce landsliding, failure and liquefaction of subsurface sediment, and ground rupture along faults. As an illustration of the problems, this submission deals specifically with the question of building across active faults. We recognise that this is not usually the main contributor to death or injury in an earthquake, but it is the most straightforward hazard to identify, and surface rupture on known active faults is the most easily avoided seismic hazard.
Earthquake damage close to faults
It is possible that any fault may move in an earthquake, but those classified as active faults (see explanation of terms on last page) are particularly hazardous because there is a likelihood that they may move again within a period of tens to thousands of years (i.e. within the lifetime of a structure). There is compelling evidence of the concentration of damage along faults that ruptured within historic time. For example, the 1971 San Fernando earthquake in California was associated with extensive surface ruptures that damaged homes, commercial buildings, and transportation routes. Recent 1999 earthquakes in both Turkey and Taiwan have shown belts of concentrated damage along faults that ruptured.
Such ruptures of the ground surface are often not a narrow line, but may be a zone up to tens of metres wide.
How can fault rupture damage be minimised?
Most active faults form scarps or terraces on the ground surface that can be mapped using aerial photographs, and then walked-out on the ground. Active faults identified this way are often then trenched to confirm that they are indeed faults, and to give information on when they have moved in the past.
Once an active fault has been identified, the only effective way to avoid fault rupture damage is not to build across it, or very close to it. Within New Zealand a limit of 20 metres away from an identified active fault is generally recommended, which is virtually the same as the California set-back distance of 50 feet.
Some faults are not able to be precisely located. For example, a good clear trace may be separated by a gap from another fault trace which is aligned along it. Such cases require more extensive investigation, and prudence would suggest not building in such a locality unless likely faulting could be disproved.
Why is there a problem?
If the location of active faults is fairly straightforward, why is there a problem in ensuring that building are not built across them? There is a combination of three factors which typify the problems with the application of the Resource Management Act to natural hazards:
1. There is no organised link between scientific information and land information such as a national inventory of accurately located active faults that is tied to cadastral land data. Although there is a considerable amount of existing scientific information, in many areas it is not easily accessible for planning purposes. Any inventory needs to be able to be updated as new information comes to hand.
2. There are no national guidelines about how such information could or should be incorporated into district schemes. Some regions or districts have accurately located hazards such as faults, whereas others have overlooked them, or only include vague statements in their plans.
3. There are no national guidelines regarding building on or close to active faults. Some local authorities prohibit such building in their district schemes, whereas others assume that this is something that will be dealt with under the Building Act.
The problem of responsibility
The Resource Management Act has deliberately moved away from national to regional control in order to give local authorities greater responsibility for their own regions. We believe that this is simply not working effectively in areas such as natural hazards because a degree of national consistency and co-ordination is desirable. Many hazards, such as active faults, extend across regional boundaries. We cannot suggest the best political solution, whether it be legislation, a national policy statement on natural hazards, or national guidelines, but feel that the case for national consistency is compelling.
The California Model
The state of California faces similar problems of high seismic risk to New Zealand, but with higher population density. Because of damage from past earthquakes over the last century, the state has acted positively to minimise seismic damage by passing two acts in conjunction with a strict building code:
The Alquist-Priolo Earthquake Fault Zoning Act (1972) was passed to prevent construction of building used for human occupancy on the surface trace of active faults. This Act has established regulatory zones around the surface traces of active faults, and special investigations are required for any proposed construction within these zones. If an active fault is found, a structure for human occupancy cannot be placed over the trace of a fault, and must be set back (generally 50 feet).
The Seismic Hazards Mapping Act (1990) covers non-surface fault rupture earthquake hazards, including liquefaction and seismically induced landslides. This allows for the definition of Seismic Hazard Zones, that include areas likely to be adversely affected and fail during an earthquake. Site-specific investigation must be undertaken before any construction can be approved.
In our opinion these two acts together provide a good model for mitigation of earthquake hazards. There is little point in re-inventing a New Zealand solution, when the arguments and precedents have already been thoroughly debated in California, where there is also a substantial body of case law covering earthquake hazards. We are not necessarily suggesting that the acts could or would be adopted in New Zealand exactly as applied in California, but rather that the principles could be easily applied.
- We believe that there is an urgent need for national consistency in the approach that local authorities take to the avoidance and mitigation of natural hazards. In a seismically active country such as New Zealand, earthquake hazards should be specifically identified in the Resource Management Act.
- Alternative solutions for incorporating earthquake information systematically into planning documents include a code of best practice, a national policy statement, or legislation. These alternatives need to be debated.
- There is an urgent need for national consistency in the identification and mapping of active faults and other known earthquake hazards on regional and district plans. This should use all available scientific information, and should include provision for regular updating as more information comes to hand or existing information is modified.
- California legislation provides a model for the problems being faced in minimising seismic hazards, with more than a decade of application. We should make use of this experience rather than assuming that our problems are unique.
- Recent experience in large earthquakes in California, Taiwan, and Turkey shows that predictable damage occurs along large faults that ruptured in historic time. This hazard is easily avoidable by banning building across or close to active faults.
S. Nathan, President, Geological Society of New Zealand, 25 September 2000
Becker, J; Johnston, D 2000: District plans and regional policy statements. How do they address earthquake hazards? Planning Quarterly: 22-23
The Geological Society of New Zealand has over 700 members, including most professional geologists within New Zealand. It is a member body of the Royal Society of New Zealand.
EXPLANATION OF TERMS
A fault is a fracture in the crust of the earth along which rocks on one side have moved relative to the other, usually at the time of an earthquake. Most faults are the result of repeated movements over a long period, and because of this the rocks close to a fault are often crushed and broken.
Fault rupture, which occurs during earthquakes, almost always follows existing faults, which are zones of weakness.
A fault trace is the line on the earth‚s surface defining the fault
An active fault is one that has moved at least once in geologically recent time. In this submission we adopt the Californian definition of movement within the last 11,000 years, rather than the longer period of 125,000 years used on many New Zealand maps.
Because faults are planes of weakness, often associated with zones of crushed or broken rock, the ground immediately adjacent to a fault often has poor foundation conditions.