Councils Fudge Christchurch Seismicity

There has been huge interest in the research I reported in my blog posting entitled Faulty Thinking About Christchurch. This research showed that work had been done in the late 1980's and early 1990's in New Zealand - by the Earthquake Commission and by the NZ Institute of Geological and Nuclear Science - about the risk of an earthquake event in Christchurch.

In particular this research warned that:

every 20 years, an earthquake of Modified Mercalli scale VII can be expected in Christchurch (slight damage in well-constructed buildings; slight to moderate in well-built ordinary structures; much damage in poorly constructed buildings; chimneys broken)

and every 55 years an earthquake of Modified Mercalli scale VIII can be expected (Damage is still only slight in structures built to be earthquake-resistant; among substantial ordinary buildings there is much damage and some collapse. Poorly built buildings are substantially damaged. Tall things such as chimneys and monuments collapse. Heavy furniture is overturned).

The purpose of this posting is to report what I have learned about the response of Christchurch Regional Council (Environment Canterbury) and of Christchurch City Council to these warnings, and how they have fulfilled their duties under the Resource Management Act (RMA).

Indications are that the Christchurch seismic risk has been systematically minimised by both Environment Canterbury and Chriscthurch City Council.

Section 30(1)(c) of the RMA states:

"Every Regional Council shall have the following functions for the purpose of giving effect to this Act in its region... the control of the use of land for the purpose of.... the avoidance or mitigation of natural hazards...."

In Environment Canterbury's (ECan) website we read under a heading: "Earthquake Hazard and Risk Assessment Study" that:

Environment Canterbury needs to know the likely impact and consequences of a major earthquake on Christchurch, to fulfil its hazard mitigation and emergency management functions. Environment Canterbury considers that the earthquake hazard information currently available is generally of a standard and scale suitable for an earthquake risk assessment.

This webpage goes on to describe work that was done for ECan by OPUS Consultants in 2005.

In the Executive Summary of that OPUS report we read:

A methodology has been developed to undertake an earthquake risk assessment for Christchurch. The approach has been based on generating risk information that meets the objectives of Environment Canterbury and provides a basis for organisations to undertake risk management actions.... An assessment of the risk from earthquakes to Christchurch will assist with the management of the risk, through reduction, readiness, response and recovery planning.

Toward the end of the substantial report there are more than 20 recommendations, among which are these:

Environment Canterbury will be commissioning an earthquake risk assessment study for Christchurch. The objectives of such a risk assessment are to understand the likely impact and consequences of a major earthquake on Christchurch, to fulfil its hazard mitigation and emergency management functions, and provide information to stakeholders for them to fulfil their responsibilities under the Civil Defence Emergency Management Act. The following recommendations are made:

(i) A risk assessment study be carried out as envisaged to provide information for risk management planning and implementation by Environment Canterbury, and other stakeholders.

vii) Three earthquake scenarios and a possible fourth scenario be used for the risk
assessment, to provide earthquake risk information to enable emergency response
planning for a range of scenarios. The fourth scenario of a hidden Canterbury
Plains Fault earthquake should be discussed with seismologists as part of the risk
assessment, to decide on the appropriateness for this study.

(ix) The liquefaction ground damage map for the Alpine Fault compiled for ECan be
extended to present liquefaction ground damage for earthquake scenarios.

xv) Casualties be assessed based on day time and night time population distributions, based primarily on building damage.

xxiii) The study be carried out based on a robust understanding of the performance of buildings and lifelines in earthquakes and the earthquake hazards affecting
Christchurch.

As far as I can tell, none of these recommendations have been followed up. I repeat the sentence that is set out in ECan's website: "Environment Canterbury considers that the earthquake hazard information currently available is generally of a standard and scale suitable for an earthquake risk assessment." I read that as: don't call us, we'll call you.... But before I move on from that 2005 Opus report, I note some of the information and comments made in the body of the text about the risk of earthquake in Christchurch - based on a literature search:

Beca Carter Hollings & Ferner (2004) report on the outcomes of the Christchurch Liquefaction Study for Environment Canterbury. Liquefaction maps are provided for two groundwater levels, and indicate high, moderate or low liquefaction potential, depending on whether liquefaction is likely in 0.12g, 0.2g or 0.34g earthquake shaking levels. (Ed: Anyone seen these maps?)

The Earthquake Hazard in Christchurch (Elder et al, 1991) presented a detailed evaluation of the earthquake hazards in Christchurch, and contributed to a significant advance in the knowledge of the earthquake hazards in the city. It considered earthquake fault sources, a prediction of the intensity of ground shaking (with associated probabilities and recurrence intervals) ... It also presented some generic comments on the potential damage to buildings and infrastructure. However, this did not provide a formal assessment of the risk....

Risks & Realities, a report of the Christchurch Engineering Lifelines Group (Centre for Advanced Engineering, 1997) presents a multi-disciplinary approach... It discusses three potential sources of earthquakes:
1. Moderately large to large earthquake in the Canterbury Foothills or North Canterbury
2. A very large earthquake on the Alpine Fault
3. Earthquakes centred close to Christchurch

The first two scenarios were considered to be capable of causing MM VIII to IX shaking intensities on the Modified Mercalli Scale, and the third MM VIII intensity.

The lifeline study adopted a 150-year return period earthquake with shaking intensities of MM VIII – IX over most of Christchurch. There was disagreement between researchers as to the expected intensity of shaking in a 150-year return period earthquake....

And then the report gets buried in a morass of conflicting data about ground accelerations and spectral accelerations, and confusion between the effects of local and alpine fault originated earthquakes, but continues to assert "there remains the potential for “hidden” earthquake sources...". The Opus report does not appear to question the earthquake predictions of Elder, but there is much talk in the report of 475 year return period earthquakes and 1000 year return period earthquakes....

In fact, the clarity of the original Elder work done for EQC in 1991, which was based on 150 years of known earthquake history, gets lost in all this confusion. However the report does state: "Information of the North Canterbury fault and fold belt is noted to be limited..."

And that was that for the 2005 Opus report. It was as if oil had been poured on troubled water. Nothing else appears to have happened. Almost a case of "we don't really want to know what the seismic risk is here - otherwise we might have to do something about it...."

There are other interesting pieces of information on the ECan website. For example there is the 2008 Q-Files Earthquake Booklet, and there is an information packed sheet entitled: Solid Facts About Christchurch Liquefaction. While these are interesting, I don't consider that by themselves they fully discharge ECan's duties under the RMA.

I checked this by investigating ECan's Regional Policy Statement (RPS) which is where you would expect to find any policies that ECan has in respect of natural hazards and in particular - earthquakes. These are very long and challenging documents at the best of times, so I have been selective. Chapter 16 is about Natural Hazards. It begins with some promise:

Chapter 16 Natural Hazards.

Natural hazards in Canterbury can be ranked by the potential damage that could result, for example, taken on an annual basis. Limited information suggests that the most severe regionally significant natural hazards in the region are, in order of importance:
(1) Large magnitude earthquake affecting Christchurch.
(2) Extreme drought.
(3) Waimakariri River flooding of Christchurch and Kaiapoi.
(4) Major tsunami affecting southern Pegasus Bay and Banks Peninsula, or Timaru coastline.

Other natural occurrences of importance include flooding, fire, wind, snowfall, landslip, erosion and sedimentation (including dune build-up), but the relative impact of these, and what degree of management, if any, is warranted, has yet to be determined.

Sounds like a call for a risk assessment. But wait. There's more to be fair. Regional Policy Statements are required by the RMA to contain: objectives, policies and methods. So here's Objective 1:

ECan RPS Chapter 16 Objective 1
Avoid or mitigate the actual or potential costs of loss or damage to life, property, or other parts of the environment from natural hazards.

Principal Reasons
Natural hazards can result in loss or damage to people, property, or the environment. The aim of natural hazard management is to minimise the net cost of such damage.

Policy 1
In managing natural hazards, highest priority should be given to the combination of measures which delivers the greatest net benefit.

Explanation
Priority treatment of natural hazards is a policy of dealing first with those that offer the highest return on available investment. This is expressed in terms of protection gained and costs incurred, a notion embodied in the term used above - greatest net benefit. In the calculation of benefit, and of costs, both monetary and non-monetary values are included. Nonmonetary factors include effects on people, cultural values, ecosystems, landscape, and amenity. These values are taken into account by comparing alternative options. Although it is not possible to place a precise dollar value on any improvement in non-monetary benefit, methods are available for gauging whether or not the additional non-monetary benefit exceeds any added monetary cost.

Net benefit, then, is the sum of net monetary benefit, and net non-monetary benefit.

A natural hazard is the interaction or potential interaction between a natural occurrence and something of value to people (ie, assets).... Consistent with this, one natural occurrence may give rise to several natural hazards. A single flood for example, may affect some homes and their occupants, some farmland, a major bridge and an airfield. Each of these interactions is a separate natural hazard. Likewise a single earthquake may affect a main highway and a town.....

For the purposes of this policy, it is these six distinct natural hazards (interactions between a natural occurrence and people and their homes, farmland, a major bridge, airfield, highway and town), not the two hazard triggers (flood and earthquake), that are to be prioritised....

Principal Reasons
Resources for dealing with natural hazards are limited, and it is important to put that investment first in the places where it is likely to do most good.

Methods
1. The methods used or to be used by the Regional Council are:
(b) Regional plans
(d) Information provision
(f) Advocacy, promotion and co-operation

2. District/city councils in the preparation, variation, change, or review of district plans, through the exercise of their functions should, where their responsibilities for natural hazards are stated in this Regional Policy Statement, consider including provisions that:
(a) give highest priority to managing those natural hazards where the greatest net benefit can be delivered.

So. The guts of this appears to be that for this policy, earthquakes are not prioritised, but their effects are. (Presumably that would be why a risk assessment was thought to be needed at one time...) And that maybe Christchurch City Council has responsibility - but only if ECan's RPS states they have responsibility.

My take on what happened is this: Figures of around $1 billion crop up in ECan thinking as the predicted cost of damage to Christchurch of an earthquake (compare with the actual estimated cost to date of earthquake damage of $20 billion). Combine this with preliminary Opus earthquake return predictions of every 475 years or every 900 years, and you can see that ECan's "cost-benefit" calculations would under-estimate the danger of the Christchurch seismic situation by a factor of 100 at least.

Clearly we need to plough on into the ECan RPS. To the next policy. To Policy 2:

ECan RPS Chapter 16 Policy 2
For the Canterbury region, or any part of the region, which local authority shall have responsibility within its own area for developing objectives, policies, and rules relating to the control of the use of land for the avoidance or mitigation of
natural hazards shall be determined in the following manner:
(a) Particular responsibility for any particular hazard or group of hazards shall initially remain with the local authority or local authorities managing that hazard or group of hazards as at 1 January 1994. Where this responsibility is not clear, the Regional Council shall retain primary responsibility....

Explanation
Natural occurrences that have a potential for adverse effects on people, property, and the environment come in many forms, among them earthquake, tsunami, erosion, landslip, wind, fire, drought, and flooding. Unless the Regional Policy Statement states which local authority or combination of local authorities is responsible for particular natural hazards, the Regional Council retains primary responsibility. Under this policy, the particular responsibility being undertaken initially remains with the local authority or local authorities managing the particular natural hazard at the time the policy was prepared. Subsequent to the Regional
Policy Statement becoming operative, the Regional Council will consult with territorial authorities in the region on any need for a re-allocation of natural hazard responsibilities, and may as a result prepare a change to the Regional Policy Statement.

“Managing” in the context of this policy includes taking particular responsibility for a particular hazard or group of hazards.

It should be noted that under the Building Act 1991, a building consent must be issued by a territorial authority, and that under the RM Act control of the subdivision of land is a function of territorial authorities.

Principal Reasons
To make clear for any particular natural hazard in Canterbury, how it is to be decided which should be dealt with by the Regional Council, and which by city and district councils.

Methods
1. The methods used or to be used by the Regional Council are:
(a) Responsibility for managing natural hazards
(g) Use of other legislation

This is a remarkably convoluted policy. It appears to say that ECan has responsibility, unless its RPS states that Christchurch City Council has responsibility. But it's about as clear as mud to me whether ECan or Christchurch City Council shoulders RMA responsibility for earthquakes in Christchurch City. And then we get to Policy 3.

ECan RPS Chapter 16 Policy 3
Where there is no provision for natural hazard in a plan relevant to an area in which an application for a resource consent has been received, the consent authority should, when having regard to this Regional Policy Statement, take a precautionary approach to the potential for a natural hazard to be created or increased as it relates to the applicant or any other person or property. This may be achieved by giving priority to the principle of avoidance.

Explanation
Many natural hazards have yet to be dealt with in plans or strategies, and many others are of such a localised or minor nature that they are never likely to be. The Regional Council and territorial authorities in the region, when considering applications for resource consents must, among other things, consider the possible natural hazard effects of granting such applications. This policy gives priority in those situations to keeping assets away from sources of danger.

Ok so this is about precaution. If no hazard management plans or strategies exist "...keep assets away from sources of danger...". This presumes knowledge of the sources of danger.

Which brings me to Christchurch City Council's District Plan (CCCDP). Man oh man. You're doing well to get this far.

In the Issues for Christchurch section of the CCCDP, Section 3.4, Natural Hazards, we read:

CCCDP 3.4 Natural hazards
Within Christchurch there is risk from a number of natural hazards including:
• possible sea level rises;
• erosion of the coastline and rivers;
• erosion of the Port Hills;
• flooding from the rivers and the coast;
• damage caused by high winds;
• earthquakes; and
• fires in rural areas....

Both the Canterbury Regional Council and Council have responsibilities under the Act for control of the use of land for the avoidance or mitigation of natural hazards. The Regional Council has considerable knowledge about river and coastal processes that give rise to the major natural hazards. The Act requires the Council to hold records of areas subject to natural hazards and has considerable expertise in earthquake standards, flooding and erosion control measures....

Nothing particularly unexpected there. But the collective ECan and CCC is worrying. Continues the concern that here is an issue that is falling between two Council stools.

CCCDP 3.4.5 Earthquake risk

Christchurch lies on the edge of a seismically active region. Consequently, earthquakes are likely to occur at a magnitude which will have major impacts on the City. In addition, there are other areas of active faults close to Christchurch, including Pegasus Bay, Porters Pass, Ashley and Mt Grey, Hope and Lake Heron.

The two main hazards which result from earthquakes are earth deformation (ground surface rupture) and earth shaking (liquefaction, land sliding, ground-cracking, tsunamis).

Strong shaking associated with either a close small magnitude earthquake, or a large magnitude distant event could cause considerable damage to the City, in particular in urban areas.

While single or two storey timber-framed residential dwellings are unlikely to suffer much structural damage in these events, in some areas liquefaction (where the solid ground takes on liquid qualities due to increased pressures) could cause distortion of buildings. Damage to buried cables, water and sewage pipes could also occur.

The most susceptible areas to liquefaction are those with water saturated, loose, well soiled silt and sand. It is also common in peaty soils. Large parts of the eastern suburbs and area around the Heathcote River are underlaid by these materials....

That all rings fairly true. So what are the objectives, policies and methods for dealing with this issue? Well here they are:

CCCDP 2.5 Objective : Natural hazards

To avoid or mitigate the actual or potential adverse effects of loss or damage to life, property, or other parts of the environment from natural hazards.

Reasons
There are a number of potential natural hazards which can affect land within the City. These hazards include the following:
• Flooding from the Waimakariri River, or the river systems within the City, particularly the Heathcote.... etc etc and;
• Seismic activity and liquefaction; etc...

2.5.1 Policy : Presence of natural hazards

To control development within the City to protect life and investment, taking account of the presence of natural hazards and the degree of risk that those hazards impose on the environment.

Explanation and reasons

Natural hazards occur in varying degrees, and may cover greatly different areas.....It is not practicable, either through regulation or other means, to provide total security and protection from natural hazards. The protection of life and investment from natural hazards needs to take into account the likely risks as a result of natural hazards that may affect them. In undertaking measures which may involve intervention in the development or subdivision of land, the Council needs to provide a balance between economic and community needs and any proposals for land use controls, particularly where lower risk and the severity of likely impacts to property is apparent, and mitigation measures are effective and environmentally sound....

2.5.3 Policy : Earthquake

To ensure that buildings are constructed in a manner (or where appropriate, reconstructed) to ensure that their stability in times of earthquake is sufficient to avoid, or at least minimise, loss of life or damage to property.

Explanation and reasons

Christchurch is subject to a reasonably high level of risk from seismic activity and there are limitations to the degree of protection that can be provided from this hazard. However, there are provisions under the Building Act which ensure that new buildings are constructed to a standard which ensures that they have adequate resistance to seismic events. Where appropriate, existing buildings can be upgraded to provide a higher degree of protection. This latter matter has to be balanced however, after taking account of the Council's life safety obligations detailed in the Building Act, with recognition that some buildings would have to be demolished if protection to full earthquake standards were required, as the cost of upgrading would be uneconomic. The Council will in these circumstances take into account the potential land use activities and the risks to life within buildings of this nature, as well as the heritage values of buildings where this is appropriate.

Implementation

Objective 2.5 and associated policies will be implemented through a number of methods including the following...:
• Pattern of zoning that limits development of hazardous areas, e.g. South New Brighton Coastal Hazard Area;
• City rules for Subdivision and Development, including esplanade reserves or strips, and rules for natural and other hazards;

Other methods....:
• Provision of information, e.g. maintenance of information on the extent and location of hazards, (Council's Hazards Register).
• The provisions of the Building Act 2004, such as conditions on building resistance to seismic events.

These words are all good, but little happens on the ground with these sorts of methods unless they are strongly enforced, monitored, and compliance measured. By contrast the methods adopted for flooding (rain - not liquefaction flooding) are extensive. The driver for the difference appears to be that earthquakes "hardly ever happen" (no surprise when you change the return period from 20 years to 475 years), while floods are frequent. Crude cost-benefit calculations complete the policy damage.

Generally, as far as I could find, there are no liquefaction maps anywhere - though there now does appear to be some liquefaction reference on property LIM files. I am uncertain when that was implemented. This is private information. Does taht system constitute a "hazard register"?

You can search the CCCDP. I looked for liquefaction. It's only in the references I have already given above. You won't find it anywhere else. But it used to be scattered throughout the District Plan.

As you will see in the final case study (below) I wonder whether the Council paid any heed to its own plan, weakened as it is by a shakey earthquake risk assessment.

In my research I came across CCCDP Plan Change 28. This relates to a large chunk of land at Ferrymead.

This is the Plan Change map. And here's how the land is described: "A large tract of land between Heathcote Village and the Heathcote River remains relatively undeveloped, despite in some cases having been previously zoned for intensive activities. Containing approximately 194 hectares, it is bounded by the Lyttelton railway line, Tunnel Road, Heathcote River, Bridle Path Road and Heathcote Village and incorporates the Ferrymead Historic Park. The Historic Park apart, the majority of the land is used for grazing and horse training purposes. However, it also includes important wetland and reserve areas along the banks of the Heathcote River...."

This Google Earth picture shows the land, and you can see where the land to be re-zoned lies. That its boundary is largely formed by the Heathcote River. The Plan Change was to allow the land to be rezoned for commercial/industrial purposes.

In this map you can see the area of land to be re-zoned, and how it was treated by Government "red", "orange", "green" zones. In fact it is in a "white" zone. hasn't yet been labelled.

It was labelled in the NZGNIS work of 1995 though, and you can see that here. In fact it is on land that is at "moderate risk" of liquefaction. Interestenigly, the 2005 Opus report makes specific reference to this land in the following terms: "Soils & Foundations (1999b) also assessed the potential for liquefaction in the Ferrymead Special Planning Zone along the Heathcote River, and concluded that of the 11 sites investigated, 5 had a medium to high probability of liquefaction and lateral spreading in a moderate earthquake (450 year return period) and an additional 3 sites had a similar probability of liquefaction in a large earthquake (1000 year return period)." (I suggest that these return periods be taken with a grain of salt for reasons already given.)

This is a section of the plan change documentation. You can read it better if you click it. You will see it talks about the need for a setback of buildings from the Heathcote River. The old plan noted a reason for a 50 metre setback was to: "minimise the risk of damage to buildings and infrastructure from liquefaction." But that objective was deleted in the plan change. It's gone from the public record.

I wonder what other changes have been made to Christchurch City Planning documents to remove references to the inconvenient truth that it has always been an earthquake prone city, ignoring the "build to the conditions" message that has been consistently delivered by consultants for the past two decades.

Christchurch Earthquake Newspaper Archive

Here a few newspaper stories from the Christchurch earthquake archives that I have scanned for your interest. If you click the images you can see them enlarged at a good resolution.... The Wellington Independent, Volume XXIV, Issue 2847, 10 June 1869, Page 6, carried this story about the 1869 earthquake in Canterbury which severely affected Christchurch. NB: this was before the Cathedral was built.

SERIOUS EARTHQUAKE CHRISTCHURCH CATHEDRAL SPIRE KNOCKED DOWN. Runs the headline in this story run in the Evening Post, Volume XXXVI, Issue 54, 1 September 1888, Page 2. The news stories go for some time as to how the spire was repaired. It was a tall order.... Apparently some of the stonework ended up in Colombo Street.

HEAVILY SHAKEN, runs the headline in this Evening Post story, Volume CIV, Issue 152, 26 December 1922, Page 8. Not as strong as some of the previous ones. Certainly not as damaging as the Cheviot earthquake in 1901 described in my "Faulty thinking..." posting below.

...here that news story continues. It's worth a read. Maybe it tells us all we need to know about why these previous earthquakes have been ignored - certainly by the media anyway. It's almost treated as a joke. It's always someone else - or someone else's chimney, or church spire, that falls down. Maybe it's better to laugh and joke about something you can't control. Sort of larikan kiwi laughing on the terraces while Christchurch crumbles. Where does the memory of a city reside? Archives (where no-one goes)? Council (which sits on inconvenient truths)? Media (which does not want to be blamed for negativity - bad news stories turn off the investment tap)? Maybe that's why we have the EQC - because earthquakes happen.

Faulty Thinking About Christchurch

(NB: Since putting up this post, I have posted further research which you will be interested to read if you want to understand how Christchurch Council planning failed to manage the city's seismic risk: How Councils Under-Played Christchurch Seismic Risk.)... but read this one first....

Maybe I read the wrong newspapers, but around the time of the September earthquake in Christchurch, I got the impression that it came as a very big surprise to all concerned. I got the impression that people thought Christchurch was safe as houses as far as earthquakes went. Not quite the last place on earth for an earthquake, but low risk. Well. That was the impression I got from what I read, and from people I know who live there. How wrong I was.

My last blog on this subject reported a few of my speculative thoughts on the matter, and quoted from the abstract to research by the NZ Institute of Geological and Nuclear Science (NZIGNS), published in Environmental and Engineering Geoscience 1995, and entitled Geology of Christchurch.

It took a while to track down the actual report itself, but I found it buried within the Serials section of the General Library at Auckland University. There are 61 pages of it covering many aspects of the geology of Christchurch and a detailed section on the risk of earthquakes there.

My reading of the data suggests that between 1869 and 1988 there have been 12 earthquakes bigger than 6.0 on the Richter Scale within 150 kms of Christchurch. Two of these were 7.0 and larger. The report contains this photo of earthquake damage to the Cathedral spire from an earthquake in 1888, and reports that the Cathedral was also damaged by earthquake in 1922 (a magnitude 6.9 earthquake centered around Motunau) and in 1929 (the Murchison earthquake). I discovered newspaper reports in the National Library that it was also damaged by the Cheviot earthquake in 1901.

The NZIGNS report tabulates 59 earthquakes that were “felt in Christchurch” between 1946 and 1994 (9 of these were centered outside the central South Island). Interestingly, the report tabulates the intensity of these earthquakes within Christchurch in terms of the Modified Mercalli Scale and the Richter Scale. Modified Mercalli Scale I. Very mild movement, only detectable by instruments. II. Some people feel a slight movement, particularly on upper floors of buildings. Suspended objects such as chandeliers may swing. III. People indoors feel some movement, similar to passing traffic. IV. Motion is felt by most people indoors and some outdoors. Windowpanes and kitchen utensils rattle; parked vehicles rock. The movement is great enough to wake sleepers. V. Felt by all people. Tall objects rock; plaster cracks and falls. VI. Alarmed, people run outside. Poorly constructed buildings begin to show damage. Motion is felt by people in moving vehicles. VII. Only slight damage in well-constructed buildings; slight to moderate in well-built ordinary structures; much damage in poorly constructed buildings; chimneys broken. VIII. Damage is still only slight in structures built to be earthquake-resistant; among substantial ordinary buildings there is much damage and some collapse. Poorly built buildings are substantially damaged. Tall things such as chimneys and monuments collapse. Heavy furniture is overturned. IX. Even in earthquake-resistant structures, there is considerable damage. Greater damage in substantial ordinary structures; more collapse. The frames structures of buildings are thrown out of plumb, and buildings are shifted off their foundations. X. Some well-built wooden structures destroyed; most masonry structures demolished with foundations. Rails bent. XI. Few if any structures remain standing. Bridges destroyed, rails greatly bent. XII. Total damage. Lines of sight and level are distorted. Objects thrown into the air. Of the 59 earthquakes “felt in Christchurch” between 1946 and 1994, 47 were MMIV in intensity (ie IV on the Modified Mercalli Scale), 9 were MMV, and there was a MMVII (this was the 8 March 1987 earthquake centred in Pegasus Bay.) (By the way - my understanding of the damage caused by the recent earthquakes in Christchurch that these range between MMVII and MMIX in intensity, according to the Mercalli Scale. Parts of Christchurch were harder hit than others.) The NZIGNS report (dated 1995 remember) states: “Dibble and others consider the 5 June 1869 New Brighton earthquake to have been the most destructive since European settlement. This earthquake is estimated to have produced intensities of MMVII-MMVIII at Christchurch, and reports of the observed effects are consistent with an M5.75 earthquake (Richter Scale) located 10 miles from the city centre…” (NB: the nave of Christchurch Cathedral was not built until 1881.) I found these reports about that earthquake and one that came shortly after: 5 June 1869: Earthquake in early ChristchurchOn 5 June 1869, Christchurch settlers were shaken by an earthquake centred beneath the city, possibly around Addington or Spreydon. The earthquake was probably shallow, with a magnitude of about 5.8. There was damage to stone buildings and the spire of St John’s Church on Latimer Square, and many fallen chimneys. The quake may have caused some ground settlement in the Heathcote Estuary, as locals describe the tide as running higher up the Heathcote River afterward. 31 August 1870: Earthquake near Banks Peninsula On 31 August 1870 the Canterbury region was shaken by an earthquake with an estimated magnitude of 5.8, centred south of Banks Peninsula, near Lake Ellesmere. Damage was minor in Christchurch—a few fallen chimneys and some structural damage to buildings. Shaking at Lyttelton and Akaroa was much stronger, with rocks falling from cliffs around Lyttelton harbour. Anyway, getting back to the NZIGNS report. It goes on to consider the risk of liquefaction, and reports past liquefaction events in these terms: “…Only one instance of liquefaction during an earthquake is recorded from the Christchurch area. This was for a magnitude M6-7.5 earthquake which occurred on 16 November 1901 (intensity MMIX in Christchurch) centred near Cheviot in north Canterbury…. ‘it was reported in The Press that at Kaiapoi the earthquakes of the 16th inst.were felt with great violence; that at some places the earth opened and water and sand were emitted from vents in the ground and that at one time an inundation by water from this source was apprehended…’”

I had a further hunt around for information about this earthquake and found these press photos and this story about what happened in Cheviot reported at the time in The Star: “A terrible earthquake occurred at 7.45 this morning, travelling direct from, east to west. It lasted several minutes. There is not a brick building or chimney left standing. The windows in many houses were shattered to atoms. One little child was killed by a falling house. The bakers' ovens are broken to pieces, and everything in the district is a complete wreck….”

Note the power of this earthquake - "no brick building left standing...." Newspaper reports at the time record a string of aftershocks, the fact that people became exhausted, would not return to their homes, camped in the fields. That the Cathedral spire was damaged. This is the Evening Post newspaper report about what was seen at Kaiapoi during the Cheviot centred 'quake: “…When first shock had passed, Mr. W. Waites, who owns an orchard and garden at the end of Charles and Sewell streets, noticed that his land was' apparently flooding from springs having been opened. It was then discovered that across his land, and part of Mr. Dunn's section, and over the surface of a paddock of several acres held by Mr. J. Sims, fissures from 1in to 3in in. width, and several chains in length, had opened… From these earthquake openings the water was freely issuing in such volume as to cause… probable inundation. Fortunately the rapid expansion of water seemed to be checked by a liberal supply of sand from some grey quicksand layer below the level of the river, and this was deposited in the orchard and elsewhere in the shape of round and oval porridge pots… The water, which had risen about six inches in on hour or two, disappeared by percolation, leaving the sand deposits in different fantastic forms….”

The 1995 NZIGNS report includes this “liquefaction potential map” of Christchurch, with high, medium, low and no liquefaction risk zones marked. The report confirms that the materials that are most susceptible to liquefaction are water saturated, loose, uniformly graded silt and sand, and notes that liquefaction has been observed in loose sandy gravels (overseas examples given). The report states: “some of the Christchurch metropolitan area is underlain by similar materials, particularly large parts of the eastern suburbs and areas adjacent to the Heathcote River… Interbedded gravels are thinnest or absent in the central and eastern area of Christchurch where liquefaction effects and ground deformations (settlement and lateral spreading) are expected to be greatest…”

Here is a section of the “red zone” map released by Government this week which includes Bexley, Avonside and Dallington.

Note the similarity with this image which is a section of the NZIGNS map encompassing the eastern suburbs.

The NZIGNS report tabulates predictions for the likely return periods of different magnitude earthquakes that might affect Christchurch in future. These are under a section headed: “Seismic Risk”, which notes work done by “Elder and others”, and which is tabulated as the graphic to the left shows. Among other things it predicts that quakes as damaging as Christchurch has had recently (at least MMVIII) will happen every 55 years on average.

The report contains a number of warnings. It maps the existence of several known fault lines, but goes on to warn: “an absence of identified fault traces does not necessarily confirm faults are absent from a particular area. Since Christchurch and the Canterbury Plans are covered by geologically very recent deposits, it is possible that some faults have not been detected.” The report explains the significance of how close the epicentre is in terms of damage inflicted. It states: “Close to the source of a large shallow earthquake (Richter 7 or greater), widespread damage and destruction often occurs, with intensities reaching MMIX or MMX. At distances about 100km from the epicentre, intensities are generally up to MMVI…” And it warns: “It should be noted that there are known active faults significantly closer than 100km to Christchurch which could generate similar large magnitude earthquakes.” I don’t know what effect this report had in New Zealand. But it was published in an international journal whose editor (Allen Hatheway from Dept of Geological & Petroleum Engineering at University of Missouri) wrote in his foreword: “…the authors leave nothing to the imagination in the question of local and regional seismicity… clearly, there is now a case for elected officials to take note and to ask and allow local and national agency geologists and engineers, planners and consultants alike, to assist in providing enforceable seismic-withstand guidelines or regulations. More than in most cities, development of Christchurch is served by careful site examination. One has the impression that the temperate climate and tranquil setting of Christchurch belies a variety of benign geologic constraints- those that are costly mainly in terms of financial losses rather than by loss of life. The intersecting curves of increased urbanisation and frequency of occurrence of damage-oriented geologic constraints will soon begin to awaken the media and public officials, as well as the insurance companies. The time is right and the local geoscience and geotechnical expertise is ready.” Looks like it took another 16 years before anyone woke up actually.

It is not as if the New Zealand Earthquake Commission has been ignoring this issue. In fact it appears that the Seismic Risk assessments that are cited in the NZIGNS report tabulated in this blog, were in fact prepared for the NZ EQC. The same table (as above) is set out in the summary of an earthquake risk assessment that was done for the EQC in 1991 entitled: The Earthquake Hazard In Christchurch: a detailed evaluation. (The authors of this work are: Elder, McCahon and Yetton.) (You can see this summary here). The 1991 EQC report summary states, in relation to the seismic risk probabilities: These probabilities indicate that Christchurch has an overall seismic hazard level comparable to Wellington for medium intensity earthquake shaking… The greatest concern for Christchurch, located near a saturated, sand and silt rich, prograding coastline, is the potential for liquefaction…. This may cause subsidence, foundation failure and damage to services. Analysis shows that large areas of the city are underlain by sands or silts which, if sufficiently loose, would be highly susceptible to liquefaction…. The EQC report summary notes that the available data (covering the earlier earthquake events that are described above) is short, making it difficult to provide reliable predictions, given that the best predictor for the future is what has happened in the past. It states: Analysis indicates that potential exists for relatively rare but very large earthquakes (approximately magnitude 8) along the Alpine fault, which essentially marks the western edge of the Southern Alps. More frequent moderate to large earthquakes (around magnitude 6-7.5) can be expected in the Canterbury Plains foothills and North Canterbury area, and less frequent moderate earthquakes under the Canterbury Plains and Christchurch itself. The attenuation model predicts that the damage in the city from these three types of event are likely to be similar. Of the four serious earthquakes in the early city history, three occurred in the foothills and North Canterbury region (the Amuri, Cheviot and Motunau earthquakes) and one virtually beneath the city (the New Brighton earthquake). In other words, what the EQC report summary plainly says, a moderate earthquake “under the Canterbury Plains or Christchurch itself” would cause “similar” damage to a “relatively rare” big earthquake centered along the Southern Alps. This summary also apppears to address the data shortcomings that are confirmed in the later NZIGNS report, noting: We have not attempted an in-depth lifelines study for Christchurch, or included economic or sociological analysis in this report. In addition to the need for this type of work, we recommend further action from the engineering profession including a review of the current seismic loadings code, local seismic design practices and building stock. We suggest site specific studies for the Lyttelton tank farm, Bromley sewerage ponds, pumping stations, substations, hospitals, civil defence facilities, airport and key bridges. Major areas of further research include studies of sand density variations and susceptibility to liquefaction across the city; continued paleoseismic evaluation of adjacent active faults, particularly the Alpine Fault, and further investigation of the deep sediments below the city. The EQC Seismic Risk Assessment for Christchurch is dated 1991. Twenty years ago. How much of this work was ever done? How much of this advice was accepted and acted upon? There are many questions that need to be answered by those in authority. Why? I'll suggest why. This information cites four earthquakes that did severe damage in and very close to the City of Christchurch (1869, 1901, 1922 and 1987). Based on this information the EQC report predicted a return period for another equally devastating earthquake of 55 years. Given the Cheviot earthquake in 1901, and then the Christchurch February 2011earthquake - exactly 110 years later - with a couple of big ones in between, perhaps their predictions are conservative. New Zealand was advised this earthquake sequence was likely. So whose fault is it that authorities didn't act? PS: Since putting up this post, I have added two later ones which you might be interested to read: Banks Peninsula Rising - Geologic History and Historic Christchurch Earthquake Newspaper Archives