Living in the Shaky Isles: the human response to earthquakes since 1840
[This talk was given at the PHANZA conference in Wellington on I July 2011]
Earthquakes are part of life in New Zealand. From records since the start of European settlement we know that a magnitude seven earthquake occurs on average about once every ten years somewhere in the country, with more frequent, smaller earthquakes that often cause damage.
Christchurch has been shaken by several large earthquakes since 1840. But the recent earthquakes came as a terrible shock, reminding us that those without personal experience have little idea of the impact of a big earthquake.
Over the last fifty years a huge amount of research has been undertaken in New Zealand by scientists and engineers seeking to understand the effects of earthquakes and ways to lessen damage and injuries. It is one of the truisms of earthquake research that earthquakes don’t usually kill people – it’s the impact of collapsing buildings and siting buildings in hazardous places. A chain of decisions taken in the 19th and 20th centuries combined to influence the damage caused by the Christchurch earthquake.
Unfortunately the impact of earthquakes on New Zealand life and social history has been virtually ignored by historians. You won’t read much about earthquakes (or other natural hazards) in any of the standard texts. I hope that my talk today may persuade some of you that this is an important area for future research as earthquakes are part of our life in New Zealand. Discussion on saving heritage buildings needs to be well informed not just about the historic value of specific buildings or precincts but also about their foundations and the impact of likely future earthquakes. And public historians are surely aware of the insatiable appetite from the general public for information on disasters. For example, the article on “Historic Earthquakes” in Te Ara, the online encyclopedia of New Zealand, has long had one of the highest hit rates, breaking all records at the time of the recent earthquakes.
Early earthquakes near Wellington
The first arrivals in the New Zealand Company settlements at Wellington, Nelson, Wanganui and Taranaki in the early 1840s were soon aware of earthquakes. They found them alarming, and started to describe their new home as the Shaky Isles. There were complaints that the New Zealand Company had ignored this feature of New Zealand in their glowing publicity about life in a new colony. To start with the earthquakes were just an odd phenomenon. But in October 1848 Wellington was shaken by a magnitude 7.5 earthquake centred in the Awatere valley in Marlborough, followed in January 1855 by an 8.2 earthquake centred in Wairarapa. Brick buildings were devastated, including most of the commercial and government buildings. But most houses had been built of wood, and survived apart from losing chimneys.
As far as Wellington was concerned, the major long term effect of the 1855 earthquake was positive, with general uplift of the land of about one and a half metres, creating new land for a cramped town. A newly exposed strip of shoreline between Wellington and the Hutt Valley offered a safe, all-weather road, no longer dependent on low tide, and the uplift helped drain the swampy, lower reaches of the Hutt valley.
After suffering from the effects of two damaging earthquakes, it seems amazing today that a decision was made a few years later to move the capital from Auckland to Wellington. South Island MPs objected to the time taken to travel to Auckland by sea – sometimes several weeks in unfavourable weather – and were determined to move the capital to the centre of the country. A commission visited possible sites for the capital in 1864, and concluded that Wellington had the best harbour as well as room for buildings. The inhabitants of Wellington were certainly keen to gain the status and economic benefits of being the capital city. Earthquake hazard was not a concern, perhaps because MPs from other parts of the country had not experienced the damage that could be caused. There are no photos of the 1855 earthquake damage – it was a few years before cameras became readily available. Imagine how different it would be today, with instant TV coverage.
The politicians of the 1860s did not appreciate that Wellington owes its deep harbour and distinctive topography to the cumulative effects of regular earthquakes accompanied by ground movements on the Wellington Fault every few hundred years. In statistical terms, Wellington is the New Zealand city with the highest chance of a large damaging earthquake in a human lifetime.
But there was sufficient memory of earthquakes to ensure that new government and commercial buildings in Wellington were constructed of wood. The Old Government Buildings, opened in 1876, is one of the most impressive wooden structures built in this period.
Sadly it only took 25-30 years for awareness of earthquake hazard to fade. Fire was an ever-present danger with wooden buildings. By the turn of the century building in brick (and sometimes stone for prestigious buildings) was deemed safer and more permanent for those who had the money to build larger houses and commercial buildings.
Most New Zealand towns were built around a port. But although Lyttelton was an excellent port, there was no room for a town, so Christchurch was sited on the opposite side of the Port Hills on the edge of the Canterbury plains. It was based on swampy land with a meandering stream that was sentimentally called the Avon. The eastern part of the town was underlain by soft sand and mud, which has long been a problem for engineers and builders. The long-term legacy of this early decision did not appear until the recent earthquakes when areas underlain by mud suffered badly from liquefaction, and streets near the river were affected by lateral spreading.
Building stone was readily available close to Christchurch, and settlers stuck to the British tradition of constructing public buildings in brick and stone. Canterbury was prosperous in the late 19th century, leading to the development of large stone buildings, mainly in Victorian Gothic style in the central part of the town, with smaller commercial buildings of brick.
A magnitude 7 earthquake struck the Amuri district in north Canterbury in September 1888, with heavy shaking lasting 40 to 50 seconds in Christchurch. Although there was relatively minor impact in the city, the most notable damage was to the newly completed Anglican Cathedral, where the top of the spire collapsed. It was promptly rebuilt. The spire collapsed again from the shaking of another north Canterbury earthquake in 1901, and this time was replaced by a lightweight wooden frame sheathed in copper. But the long-term effect of the 1888 and 1901 earthquakes was to convince Christchurch people that their brick and stone buildings would withstand the impact of earthquakes – which proved to be true for the next 110 years.
A quiet period
The first quarter of the twentieth century was a tectonically quiet period for New Zealand, without any major earthquakes affecting large population centres. Awareness of earthquake hazard gradually diminished, and little thought was given to mitigating their impact. Every year from 1913-26 an article in the New Zealand Official Yearbook included the comment that “earthquakes in New Zealand are rather a matter of scientific interest than a subject for alarm”.
The late 19th and early 20th centuries was the time when many of the brick commercial buildings were built in the central part of towns and cities, often replacing older wooden buildings. As was typical of the time, they were built with little or no reinforcing. Some of the grander houses were also built of brick or stone. My own family followed this trend, building a two-storey mock Georgian brick house in Grant Road, Thorndon in the 1920s – as we now know, only a few metres from the Wellington Fault.
Murchison and Hawke Bay earthquakes
The Murchison earthquake of 17 June 1929 (magnitude 7.8) was a reminder of the presence of Ruaumoko, the God of earthquakes. There was considerable damage to chimneys and masonry buildings in Greymouth, Westport and Nelson. The earthquake raised awareness of the vulnerability of many buildings, but there was no action before the magnitude 7.8 Hawkes Bay earthquake struck on 3 February 1931. At least 258 people were killed – still the largest loss of life in a New Zealand earthquake - with most deaths in collapsed buildings that included a nurses’ home, hotel, department store, cathedral and old men’s home. Fire began in the business district of Napier, and the central part of town was burnt out.
The Hawkes Bay earthquake dramatically showed that building standards needed to be upgraded to include provision for earthquake resistance. Within days the government appointed a committee charged with developing new building standards. They rapidly drew up a code for earthquake-resistant construction based on guidelines developed in California after disastrous earthquakes in 1906 and 1923.
The code contained basic provisions that buildings should be tied to their foundations, that walls should be tied together at each floor, and that bracing should be symmetrical about the centre of mass of the building. Special attention was given to brick buildings, with a height limit of three stories unless reinforced with a frame. The code was to apply only to new buildings, although it was acknowledged that work needed to be done to strengthen existing buildings.
Because buildings were traditionally designed to support vertical loads, the biggest concern was their vulnerability to horizontal or sideways shaking. But how much sideways shaking should buildings be able to withstand? The Californian guideline was that they should be able to withstand the intensity of shaking of one tenth the acceleration due to gravity (0.1g) – or in simple terms, the sideways thrust of at least a tenth of its gross weight. The committee drew up draft building regulations based on this rule, and recommended that it be adopted throughout New Zealand.
Although the government agreed in principle, it was unable to carry this out. Traditionally building standards were set locally rather than nationally – each borough and county council set building standards in its own area through local bylaws. In 1931 the government had political difficulties. When a Building Construction bill was introduced in 1932 the idea of compulsory national regulations (with inspectors to enforce the standards) met so much parochial opposition that it was abandoned. Eventually a compromise led to the development of a Model Building By Law in 1935, which councils had the option of adopting – and many did not.
So, from the start the adoption of building standards for earthquake resistance was patchy, depending on the inclination of local councils. It was complicated by the argument that some parts of the country, especially Auckland/Northland and east Otago, had a lower frequency of damaging earthquakes, and therefore the standards should be less rigorous. This continues to be an issue debated by scientists, engineers and planners.
The Second World War postponed work on earthquake-resistant design, but few buildings were constructed during this period. Two large earthquakes centred in the Wairarapa valley occurred in June and August 1942, and did considerable damage in the surrounding region. In Wellington, for example, over 5000 houses were badly damaged and some were not repaired for years. At that time, earthquake damage was specifically excluded from most insurance policies, which meant that there was often no money to make proper repairs. This prompted the government to set up the Earthquake and War Damage Commission (now EQC) to give basic earthquake insurance cover for homes which is linked to the payment of fire insurance – a unique New Zealand response to earthquake hazard.
Post war developments
Professor Bob Park, who became a leader in earthquake-resistant design, recalled that earthquake engineering was neglected when he went through university in the early 1950s. The standard textbook had been published in 1940, and was based on static design concepts developed in California and Japan. But this changed rapidly, with a building boom in the 1950s and 1960s requiring a local knowledge of how to build in an earthquake-prone environment. By 1968 there were a sufficient number of engineers and scientists working in the field to form the New Zealand Society of Earthquake Engineering, which has fostered research in earthquake-resistant design.
Paradoxically, the late 20th century was a period with few large earthquakes in New Zealand, so engineers and scientists gained experience from observing the impact of overseas earthquakes in countries where a wide variety of building techniques had been used. Those who travelled to overseas earthquakes were convinced that New Zealand needed to develop a philosophy of earthquake resilience, but found that they met resistance at home because the memory of the impact of earthquakes had faded.
The magnitude 7.1 Inangahua earthquake in May 1968 was widely felt over the northern part of the South Island, but was in a remote area and there was little damage to large buildings and few deaths. The smaller, magnitude 6.3 Edgecumbe earthquake, in March 1987, had much more impact because of damage to industrial facilities at the Tasman Pulp and Paper Mill, local milk processing facilities, and the Matahina Dam. This was the most expensive earthquake in New Zealand to that time, and it focussed attention on the insurance costs of damage to an industrial area as well as the long time needed for reconstruction.
One of the most innovative approaches to earthquake-resistant design has been the concept of base isolation, pioneered by local scientists, Ivan Skinner and Bill Robinson. This involves incorporating lead-rubber bearings beneath the base of a large structure that work by isolating the building and absorbing the motion and energy created by a large earthquake. Lead-rubber bearings have been incorporated into a number of large buildings in the Wellington area including Te Papa, Parliament Buildings, the Supreme Court and the Wellington Regional Hospital as well as several road and railway bridges. The invention is now being widely used worldwide in earthquake-prone areas, especially for critical public buildings such as hospitals.
After standards for earthquake-resistant design were first promulgated in 1935, they were regularly revised about once a decade to incorporate changing ideas. One of the lessons from overseas and New Zealand experience was that all large buildings need to have a degree of ductility – the ability to stretch and deform in a large earthquake – rather than simply being designed as rigid objects that have a lower level of earthquake resistance. This was a major change incorporated in the 1976 code, and since then has led to buildings being classified as pre-1976 and post-1976, the former being much more liable to major damage.
The primary aim of earthquake-resistant design is to avoid building collapse and save lives. This is not the same as regarding a building as earthquake proof – there is no such thing. There will almost always be a level of repair needed after a big earthquake, and some buildings may need to be demolished. One of the aims of incorporating a level of ductility in a building is to control areas likely to be deformed, and localise subsequent repairs.
Because of the lack of national regulations, there was huge variation in the earthquake resistance of buildings in different parts of the country. Seventy years after the first building standards were produced, the 2004 Building Act introduced some long-overdue changes to ensure compliance with the building code for both new and older buildings. All new buildings were required to be designed to resist earthquake loadings as defined in the New Zealand Building Code. Older buildings were required to meet at least 33% of the earthquake resistance of current standards, and any that do not meet this standard were classified as earthquake-prone. The Act requires territorial authorities to develop a policy to deal with such potentially hazardous buildings. Although this was a long overdue step forward, there were major problems:
1. The Act does not specify any national standards for the strengthening of earthquake-prone buildings. Each local authority is left to develop their own, with varying standards and huge duplication of effort.
2. The approach taken by each council has varied enormously. At one end of the spectrum, Wellington City Council has inspected and classified all its older buildings, issued orders to owners to bring them up to standard by a specified deadline, and made the list of earthquake-prone buildings publicly available. But other councils in the same region, where earthquake risk is equally high, have yet to inspect and classify all their older buildings, let alone take any action. Other councils have been entirely passive, only requiring upgrading of older buildings when there is a permit application for alterations.
3. Even when councils have required owners to strengthen older buildings, they have been given long periods of time, in some cases up to 30 years. In practice this may mean that a hazardous building continues to be occupied for 30 years without any earthquake strengthening, then demolished at the end of the period.
4. Most damning of all, the technical community, including the New Zealand Society of Earthquake Engineers, believes that retrofitting to 33% of the current standard is inadequate, and that 67% should be the minimum. This is supported by the Historic Places Trust, which supports strengthening to at least this level as a way of preserving our most important heritage buildings. In the severe ground shaking during the 2011 February 22 earthquake a large number of older buildings collapsed including some that had previously been strengthened.
There will inevitably be changes to sort out these and other issues in the aftermath of the Christchurch earthquakes. Already the Christchurch City Council has resolved to adopt 67% of the current building code as the minimum standard for refurbished buildings.
The inevitability of earthquakes
Over the last fifty years there have been enormous advances in our understanding of earthquakes, and how engineers can design buildings and structures to minimise damage. There was no shortage of technical information on earthquake hazards in Christchurch. For example, in 1991 a major report was prepared for the Earthquake Commission titled “The earthquake hazard in Christchurch: a detailed evaluation”. A summary is available on the EQC website at: http://www.eqc.govt.nz/research/researchpapers/p_105.aspx. At about the same time GNS Science published a detailed account of earthquake hazards in the Christchurch region. Both publications, which were readily available, identified likely impacts of a major earthquake on Christchurch, including widespread liquefaction, collapse of masonry buildings, and rock falls around steep cliffs – an accurate prediction of what has happened in the recent Christchurch earthquakes.
Earthquake hazards have long been a focus of research in the Departments of Geological Sciences and Civil Engineering at Canterbury University. In the culmination of a lifetime's research the late Professor Bob Park devoted the Hopkins Lecture in 2001 to a discussion of the earthquake hazard in Christchurch, and how engineering developments could improve the resistance of man-made structures to earthquakes.
Several journalists have recently commented that liquefaction is a new word, but this is simply untrue. Canterbury engineer John Berrill has spent much of his career investigating the impact of liquefaction, and documenting past examples in New Zealand and overseas. For example, in 1989 he prepared a report, ”Liquefaction at Kaiapoi in the 1901 Cheviot earthquake”, a summary of which has long been available on the EQC website at: http://www.eqc.govt.nz/research/researchpapers/p_002.aspx. But in the September 2010 earthquake astonishment was expressed about the extent of liquefaction around Kaiapoi – and I have yet to see any acknowledgement that the problem has been known for many years, but overlooked.
Sadly these and other technical publications had little impact. They were ignored or dismissed as scaremongering. There was continuing pressure to build in areas susceptible to earthquake damage. Despite the information the local council continued to issue permits for subdivision in liquefaction-prone areas such as Bexley and for building new houses close to cliffs or on hillsides prone to rock falls. No one believed that Christchurch would suffer a large earthquake.
It is clear that the results of scientific and technical understanding have not been matched by our ability to persuade politicians to incorporate the results of research into decision-making about urban planning. Geologists can advise how to avoid hazardous sites and engineers can retrofit earthquake-prone buildings, but unless there is political will to use this advice, the damage and casualties from future earthquakes will continue to be higher than it needs to be. The reality is that once an urban area has been laid out and permission given to subdivide and build, it may be impossible to correct mistakes before the inevitable disaster.
A message for historians
In recent years a number of histories of Christchurch City and parts of Canterbury have been published. It is noteworthy that none have more than the briefest mention of earthquakes (or other natural disasters), despite the record of past damage. One of my reasons in giving this talk at a conference of historians is to remind you that earthquakes are part of our history everywhere in New Zealand. If you, as the chroniclers of our past, don’t remember them, no-one else will
Beetham, R.D. 1992: Chapter 8 – Earthquake Hazards. Pp 75-85 in “Geology of the Christchurch Urban Area” by L.E. Brown & J.H. Weeber. Institute of Geological & Nuclear Sciences geological map 1.
Berril, J.B.; Mulqueen, P.C.; Ooi, E.T.C.; Pautre J-L 1989: Liquefaction at Kaiapoi in the 1901 Cheviot, New Zealand, earthquake. EQC research paper 2. A summary of this paper can be viewed at: http://www.eqc.govt.nz/research/researchpapers/p_002.aspx
Davenport, P.N. 2004: Review of seismic provisions of historic New Zealand loading codes. New Zealand Society of Earthquake Engineers 2004 Conference paper 17: 1-10.
Elder, D.M.G.; McCahon, I.F.; Yetton, M. (1991): The earthquake hazard in Christchurch: a detailed evaluation. EQC research paper 105. The summary of this paper can be viewed at: http://www.eqc.govt.nz/research/researchpapers/p_105.aspx
Galbreath, R. 1998: Science in the Shaky Isles – 1: Earthquakes and Earthquake Engineering.Chapter 8 (pp 201-224) in “DSIR: Making Science Work for New Zealand”. Victoria University Press.
Park, R. 2001: Improving the resistance of structures to earthquakes. Bulletin of the New Zealand Society for Earthquake Engineering 34 (1): 1-39.
Reitherman, R. (interviewer). 2006: Robert Park & Thomas Paulay. Connections: the EERI oral history series 12, 172 pp.
Royal Society of New Zealand & others 2011: The Canterbury Earthquakes: answers to critical questions about buildings. http://www.royalsociety.org.nz/media/information_paper-earthquake_engineering_christchurch.pdf