Thursday, January 24, 2013

The Canterbury Earthquakes in New Zealand

Downtown Christchurch during the earthquake

I’ve been spending some time with the events called the Canterbury Earthquakes in New Zealand and a particularly destructive aftershock that destroyed the central business district of Christchurch, a lovely little city on the South Island of the country that I visited and liked long ago.

Reading about earthquakes and cities is among the most depressing things to do that I know.  You immediately transfer the events from far away to where you now are, where your friends and family and work are.  You know not only that it could happen here, but that it already did happen here and it will happen here again and it will seriously bust up much of what you are looking at and will surely kill some people you know, or perhaps their children. 

CTV Building, Before and After
Nearly two years after the February 22, 2011 aftershock in Christchurch, a large swath of the central business district remains closed and the government is tearing down and carting off hundreds of damaged buildings.  There is alarming data about rates of depression and regressive behavior in Christchurch boys and girls who have experienced thousands of earthquake aftershocks in the past two years, more than 30 above five on the Richter Scale, several hundred above four.  People are talking about how one of the more sophisticated earthquake codes in the world could not provide the ultimate protection to 185 people who died and the thousands who were injured, several hundred seriously. 

I think about New Zealand and its position on the globe by comparing it to the west coast of the United States.  From the Canadian border to San Diego is about 900 plus miles and so is the very top of the North Island to the end of the South Island in New Zealand.  San Francisco is at nearly the same latitude as Auckland, the largest city and Christchurch is some 500 miles away to the south and roughly equivalent in our hemisphere to central Oregon.  If you go 2,000 miles west across the Pacific in our hemisphere and go straight south to the other one, you will ultimately run into Christchurch.

Juan de Fuca Plate subducting under North American Plate
Oregon State University
There are many similarities between our Pacific Northwest region and New Zealand, but the only one I’m thinking about today is that New Zealand and the Pacific Northwest share a dangerous location – both are close to the edge of the Pacific Plate.  The Pacific Plate and others like it make up Earth's outer shell, called the lithosphere. Here’s how the National Geographic describes tectonic movements:

“Churning currents in the molten rocks below propel them along like a jumble of conveyor belts in disrepair. Most geologic activity stems from the interplay where the plates meet or divide.” The edges of the plates are where earthquake activity is the greatest. In the Northwest, the Pacific Plate is moving to the north and west while the much smaller Juan de Fuca Plate, located off the shore of the Northwest, is moving east and a bit north, colliding with the west bound North American plate and subducting – diving under the North American plate. This creates our Cascade Range volcanoes, our up thrust land forms like the Olympic Mountains and, when the plates stall out for a time, make our huge subduction zone earthquakes when they let go.

In the Southern Hemisphere, New Zealand’s part of the Pacific Plate moves in the same direction as our part of it, to the northwest.  It collides with the Australian Plate, moving to the northeast.   The Pacific slides under the Australian below the part of the globe where New Zealand exists, though with a twist.  A part of it hits the Australian Plate at an oblique angle, splitting off a part of the Pacific Plate, with some of the mass heading Northwest and a piece going Southeast. The result of all this is that New Zealand is rich in earthquakes of all kinds.  One of them is the subduction zone earthquake – rupturing deep in the earth and releasing huge amounts of energy, its power attenuated by the distance it is from our daily lives unless the rupture causes a Tsunami.  However, because this earthquake lasts several minutes, its effect on tall buildings is particularly powerful.  New Zealand also has another kind of earthquake type more like San Andreas Fault in California or our Seattle Fault.  These are called ‘strike-slip,’ faults, a movement in the crust where the edges of the fault move in different, horizontal or vertical directions.  These strike-slip earthquakes are smaller than the monster subduction zone earthquakes, but they are frequently shallower and create more violent ground shaking.

Daily earthquake activity, 2008-2013
Christchurch is the capital of the Canterbury Region, one of 16 regional jurisdictions in New Zealand.  Canterbury is about the same size of the counties surrounding Puget Sound.  During the four days between the 16th and the 19h of January, 2013, the Canterbury region recorded 29 earthquakes.  Two of them, both within six miles of Christchurch occurred on the same afternoon and registered just under 5 Richter.  It is not particularly unusual to have frequent earthquakes happening in a known earthquake zone.  For example, the Pacific Northwest experienced twenty quakes during the same four days.  What is unusual about Canterbury is that the earthquake sizes are significantly greater than those now occurring in our region.  Scientists believe that this particular sequence of earthquakes began in the early hours of September 4, 2010 with a 7.1 Richter 25 miles from central Christchurch.  It was the biggest earthquake in the past 80 years, was of fairly long duration (40 seconds) and fairly shallow, about six miles.  It caused significant damage to many older buildings.  There were a handful of injuries, some damage to the water and sewer systems but not catastrophic.  Power was back on in the early evening and the airport was reopened after inspections of structures there.  Engineers and the authors of the Building Act, as Canterbury's code is named, were treated as heroes, praised in international publications.  It was serious, no doubt, but a bit like the Nisqually Earthquake that hit the Northwest in 2001 – serious, but a dodged bullet. 

Christchurch at the edge of the plain and Bank's Peninsula
Google Earth
Christchurch sits on the edge of an alluvial plain that stretches 40 miles from the Southern Alps, the highest mountain range in Australasia.  The mountain range has 16 peaks above 10,000 feet, many different and remarkably accessible glaciers and is the source of three rivers flowing out and forming the Canterbury Plains, a 150 mile long flood plain on the edge of which sits Christchurch, a town of about 350,000 people.  Christchurch is also at the edge of an unusual land form called Banks Peninsula, a rugged place created by two small volcanoes, now extinct and deeply, beautifully eroded. 

Settlement of New Zealand by Europeans began in the 1850s and the economy started with sheep as so many things in New Zealand do.  Today the area is also known for oats, wheat and other grains, viticulture, tourism, timber and yes, sheep, but also some manufactured products for the domestic market.

For all the earthquake activity in New Zealand, Christchurch was not particularly thought of as a serious earthquake prone area, even though it sits on the edges of a couple of old volcanoes and the entire country is riddled with fault lines radiating out along the edge of the Pacific/Australian Plate collision.  But both the 2010 and the 2011 earthquakes were caused by dangerous faults that were unknown before they ruptured.

An earthquake in 1931 that killed nearly 300 people on the North Island started New Zealand into the earthquake code business.  A national code was adopted in 1935 followed by revisions in 1965, 1976 and 2004 and New Zealand was considered a leader in developing earthquake codes.  A weakness, however, was that there were substantial numbers of un-reinforced masonry buildings in the Christchurch building inventory and many of them had not yet been or were poorly retrofitted.  Those that did not collapse in the 7.1 earthquake were weakened by it.  Many collapsed on February 22, 2011 and falling brick and concrete blocks killed 42 people.  In addition, one of the buildings that collapsed, the reinforced concrete Canterbury TV building, did not meet codes, was poorly designed, poorly constructed, poorly inspected and cost the lives of 115 people.  In high rise office towers, many were trapped in the upper floors.  While some buildings didn’t fail, air conditioning, lighting and other systems inside the buildings injured and killed people.

The February 22, 2011 quake struck at 12:51 PM on an end-of-the-summer Tuesday.  The 6.3 Richter event lasted just 15 seconds, shorter than the 40 seconds of the bigger, 7.1 2010 quake.  But few people were on the streets at 4:35 AM.  Thousands of people were out on the summertime, noon hour streets on February 22, 2011.

There are many different ways to describe the relative size of an earthquake.  One way is to measure the energy released by the event.  We're all familiar with the 1-10 Richter Magnitude Scale which serves this purpose.  But some earthquakes can release lots of energy but still have relatively modest effects on the built environment.  The Modified Mercalli Scale is focused on using observable events to create a picture of what has happened when the ground actually shakes.  Confused cows in a field, some chimneys tipping over, some people, though not all, feeling the ground shaking are events on the lower end of the twelve level Mercalli Scale.   However, numbers like VII, VIII or IX on the Mercalli Scale are devastating:

VII Considerable damage in poorly built structures, felt by people driving, most are frightened and run outside.  VIII Slight damage to well built structures, poorly built structures are heavily damaged, walls, chimneys, monuments fall.  IX Underground pipes break, foundations of buildings are damaged and buildings shift off foundations, considerable damage to well built structures.

Parts of Christchurch suffered all of those Mercalli values.  There is, however, another measure that points to something truly remarkable at Christchurch.  One way to measure the force of an earthquake is to measure the gravitational acceleration of the earth’s movement during a quake.  This number is expressed in percentages of one “g” -- the earth’s gravitational force of 32 feet/second/second.  Seattle’s current earthquake code wants buildings to be constructed to a ground acceleration of .4g, backed up by several other strategies in how the building is constructed and fastened together.

Christchurch was the second highest "g" force ever recorded.  Parts of the city closer to the epicenter experienced shaking measured at 2.25g and many parts of the city experienced 1.5-1.9g.  The Royal Commission of Inquiry which studied the ramifications of the earthquake, determined that the probability of such an event in the soils on which Christchurch sits was once in 2500 years. 
 
When the book on the rescue phase closed in March, 2011, the tally was 185 people dead, thousands injured, some 200 seriously.  Nearly 1400 buildings in the city were damaged beyond repair and are in the process of being torn down.  Some 600 buildings in the Central Business District have been demolished or are scheduled for demolition.  Much of the Central Business District is still cordoned off and many of its water and sewer systems are still dysfunctional.

Creating and enforcing building codes against one of nature’s most elemental acts requires interplay between some of society’s most elemental concepts.  Life.  Money.  Probability.  Knowledge.  Are we focused more on the protection of the building or more on the protection of the people in it?  Should we design a building to withstand a major earthquake every 500 years?  800?  2500?  When should buildings we know to be dangerous in certain earthquakes be retrofitted?  Now?  When major work is done on them?  Do we know enough about our seismic risk to rely strongly on the risk assessments on which our codes are written?

In Seattle, we begin the process of applying these concepts to the design of our building codes every three years, based upon civil engineering standards written by committees of experts from the American Association of Civil Engineers that are rolled up into their Uniform Building Code.  Local or state governments either adopt the ASCE code or create additional provisions to reflect their local situations.   Some communities may use a similar code developed by an international organization.  The most recent Seattle code review was completed in 2010 and will become Seattle law in 2013.  Seattle planners are already starting on the next one, to be ready in 2016.

Earthquake Hazard Map
USGS
The United States Geologic Survey creates earthquake hazard maps that are another input to the codes.  The USGS produces hazard maps for many events, including earthquakes, and we know from those maps that certain areas of the city, including the Central Business District, could have the kinds of soil accelerations seen in Christchurch.

Soil acceleration is a characteristic of the shallow, nearby, short duration event.  But what happens if we have a large subduction quake, like the ones in Sumatra or the one that created the Tsunami devastating Fukushima, or recently in Chile – Richter Magnitude 9 or above events?   Ground acceleration in those past events is much less violent – .25gs is what Seattle’s planners anticipate – but the damage comes from the duration of the earthquake – five, six, seven minutes. It's like moving a big boulder.  You can move it if you get it rocking. That kind of earthquake puts higher buildings at greater risk because of the continued rhythmic motions produced over several minutes.  

Seattle Fault
There are several elements to Seattle’s strategy.  Most people think that Seattle’s major risk is a rupture on the Seattle Fault and that is very much on the minds of today’s code writers and policy makers.  In code terms, the Seattle Fault, running loosely along the I-90 corridor in the south end of the city, is the Maximum Credible Event to which codes are written.  It last ruptured about 1100 years ago in what geologists think was about a 7.0 Richter. It is a relatively shallow fault and clearly would cause many building failures along the lines of Christchurch or worse. A dilemma for building protection is that people were unaware of the Seattle Fault until 1992.  So, many of our buildings were designed to a different set of assumptions about the ground acceleration.  Only 20 of Seattle's 89 buildings over 20 stories were built after 1992 and less than a third of our 750 lower rise buildings were built with knowledge of the Seattle Fault.  

Retrofitting buildings has always been one of the tough calls people in the earthquake trade have to make. Forcing additional cost onto a building by requiring new seismic stabilization is a touchy business. There are, for example, about 800 un-reinforced masonry buildings throughout Seattle, concentrated in some of our most important and historic neighborhoods.  If a code tips the economics of a building it can mean the building remains empty or even torn down. However, the fact that similar buildings in Christchurch killed some 42 people when they collapsed is a crucial piece of knowledge that must be considered.  Seattle’s city council may consider the topic of un-reinforced masonry buildings this year. 

Another retrofit concept turns on the systems inside the buildings.  It used to be that the job of the code was to keep the building standing and the stairs intact during an event.  But experience in past earthquakes, including Christchurch, shows that many people are killed or injured by the lighting systems, air conditioning systems and other internal building infrastructure that become detached, even though the overall building shell performed well. 

Christchurch is also heading toward requiring a kind of warning signage to the public about just what kind of building you are in.  This gives the individual a chance to assess whether he wants to be in such a building or, at the very least, increase awareness and caution while in the building. 

A key element in Seattle’s earthquake strategy is to protect the protectors.  For several years, police and fire buildings have been replaced or upgraded to afford greater protection to the people who will, ultimately, have to rescue us.  Harborview Hospital, which sits almost directly above the Seattle Fault, is the hospital many of us would go to in an emergency.  It had a major seismic upgrade in 2008.  Seattle is also in a rush to replace the viaduct and rebuild the adjacent seawall on the waterfront, whose failures would clearly be catastrophic.  

Neighborhood sewage disposal tank.  The blue line
in the background is the water main
It’s fascinating to read about post-quake life in a prosperous, western city.  Daily life in Christchurch has been a shifting and frequently difficult reality.  Because so many of the sewer and water systems were broken or filled with sand from the liquefaction that occurred, the government bought all of the port-a-potties it could, about 2,000 and another 30,000 chemical toilets. They were positioned throughout neighborhoods and business districts and available to residents.  Temporary flexible water systems snaked along sidewalks competing for space with large interim disposal stations for the chemical toilets. 

Temporary Stadium
Those households whose dwellings were dangerous, about 10,000, could not even muddle through and had to leave and live elsewhere.  The city’s stadium was badly damaged and slated for demolition so, the city’s leadership decided to build a temporary stadium to provide an outlet during the hard times for Rugby crazy Kiwis. 

Shopping area adjacent to cordoned off downtown
Commerce within the city needed temporary spaces to go back to work.  Many of businesses turned to the humble shipping container as temporary venues for selling books, shoes, providing entertainment and food, retaining a semblance of normalcy near the Central Business District as the city’s people work to define what is to come.  Temporary spaces will be a fact of life for Christchurch for many, many years. 

A leading developer in Christchurch said that the Central Business District would take ten years to reclaim and would likely have just 30% of the commercial financial volume it hosted prior to February 22, 2011.

Christchurch Cathedral
The earthquake was hard on historic preservation.  About 250 of buildings in Christchurch had an historic designation.  Just under half of them fell down, or were torn down or are scheduled to be removed. 

In the first six months after February 22, 2011, 10,000 parents sought help from mental health providers for a variety of symptoms in their children.  The constant shaking of the ground was an important factor among others.  Many children had their schools damaged or destroyed and needed to co-locate at a different school.  Many of these kids reported difficulty sleeping, exhibited symptoms of depression and regressive behaviors such as bed-wetting and thumb sucking.  They were also hyper-vigilant around loud noises.

The children were not alone in their anxiety.  Their parents also suffered.  Even though about 80% of the $16 Billion NZ in damage was covered by insurance and government home buy-back programs, jobs were lost and financial insecurity was widely spread. 

The recovery is a $30 Billion NZ project and is creating a growing business recovery in Canterbury.  Today, consumer spending in Christchurch has passed the consumer spending rate of the rest of he country.  Tourism continues slightly down but the unemployment figures are going Canterbury’s way, around 5% now, down from 8%.  Commercial and residential sales in the Christchurch CBD went from near zero in March of 2011 to $30,000,000 at the end of 2012 even with higher the higher costs of housing.  On the day of the earthquake, the year over year consumer sales index that measures inflation for housing was at 2%/year and today is now near 12%.  However, retail trade and the hotel/restaurant industry lost about 25% of its employment base and has been slower to recover.  

As the city life stabilizes, as the porta-potties, chemical toilets and the top-of-the-sidewalk-water mains disappear, as existing debris is scooped into trucks and the many remaining broken buildings get carted away, the government and its citizens have organized a discussion about what to do next.  

Future CBD
They want their downtown back, but not the way it was.  Their answer is to rebuild their downtown on a smaller scale, more dense with a greener look and feel both in the sense of open space and parks and in the context of clean/ high tech.  Their current plan is to create a greater density with much smaller buildings and more residential opportunities.  At the same time, the plan wants to embrace the river that runs through the downtown as well as on the city’s west edge.
 
The plan says that public investment will create individual nodes of activity in different parts of the town – a convention center, a new central library, a new central square, performing arts, rugby stadium and cricket pitch, Maori Cultural Center and housing.  Public investment will also provide excellent public transportation and access -- walking trails, bike lanes as well as critical infrastructure, including robust communications technology.  They assume that private investment will find enough reasons to follow the public investment and fill in complementary activities.  Since this will take many, many years, the plan anticipates various transitions of now empty spaces by programming them with art, temporary restaurants, festivals, shopping, etc.  You have to wonder if the end result will be a little Paris or a big mall.
Bare Your Bum For New Brighton

It looks like a long slog in Christchurch.  Reading the newspapers over time, you can see that the emotional pulling together in the immediate aftermath of February, 2011 has given way to some frustration, disappointment, sniping  and direct action.  You can also tell that the unforced optimism of New Zealanders, characterized by the folk saying "She'll be right," could be fraying as well.  Two Canterbury Councilors visiting a suburb, New Brighton, last December found themselves looking at 50 people on the beach staging a "Bare Your Bum For New Brighton" protest.

In the category of good news, academics have pounced on the earthquake to produce considerable research on various aspects of people's lives after the shaking stopped.  People in Canterbury have been shown in statistically significant ways to have turned closer to God.  Other research demonstrates that many people see the earthquake as shaking loose the shackles of a mundane life by turning people to more satisfying, emotionally significant experiences.  

Economic Impact of the Canterbury Earthquakes

All you ever wanted to know about chemical toilets

Canterbury Earthquake Recovery Authority

Royal Commission of Inquiry








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