Christchurch shakes : 4 September 2010 booklet.pdf · shake have complicated the ... The Earth’s crust is divided into plates ... boundaries are called fault lines. Earthquakes

At 4.35 am on September 4,2010, the people ofChristchurch and surroundingdistricts were awoken by

violent shaking, accompanied for manyby the sound of smashing crockery,breaking glass and the crash ofbookshelves, ornaments and pictures. Amagnitude 7.1 earthquake had occurred,and the shaking lasted for 30 seconds.

In that first tremor roads cracked,water and sewerage pipes ruptured,railway lines buckled, walls toppled andchimneys fell. The bells of ChristchurchCathedral were set ringing and historicbuildings fractured. Despite all of the

damage, nobody was killed.The epicentre was 40 km west of

Christchurch and the depth of the quakewas at 10 km. It is the most damagingearthquake since the Hawkes Bayearthquake in 1931. For many people theearthquake came as a complete surprise,as there have been just 3 moderateearthquakes in the area in the past 40years and any faultlines were notdetected. In the three weeks following theearthquake there were over 1000aftershocks, one of them with amagnitude of 5.1.

This made it difficult for buildinginspectors, who needed to return to look

at buildings which they had alreadycleared. Many homes have beendamaged, some so badly they will need tobe demolished, and the Christchurchbusiness community has been badlyaffected.

Experts say that the fault that causedthe Canterbury earthquake had not movedfor at least 16,000 years. The earthquakeproduced the strongest earthquakeground-shaking ever recorded in NewZealand.

The fault rupture itself occurred apreviously unknown east-west faultline,visible at the surface for 24 kilometresfrom Greendale to near Rolleston.

Christchurch shakes :4 September 2010

Adapted mainly from The Press, 12 and 14 October, 2010, and other issues

2 CHRISTCHURCH SHAKES: 4 September 2010

Scientists believe not one but threeearthquakes just seconds apartripped a gash across theCanterbury Plains and unleashed

energy equivalent to 67 nuclear bombsspeeding into Christchurch. Scientistsbelieve they have unearthed the triggerfor the Canterbury earthquake. Theirpotential breakthrough involves a secondpreviously unknown fault under theCanterbury Plains.

In the wake of the 7.1 magnitudequake, GNS Science geologistsdiscovered a new fault trace runningroughly west-east, shattering roads, waterraces and shunting shelterbelts and fencesabout three metres to the side.

A 7.1 magnitude earthquake releasesenergy equivalent of 670,000 tonnes ofexplosives, or 67 nuclear bombs of thesize that devastated Hiroshima.

“A fault beneath the CanterburyPlains capable of generating anearthquake of that size is a majorsurprise,” said Canterbury Universitygeologist Associate Professor TimDavies.

The impact upon many communitiesand towns was devastating. Most of thedamage was done in that first judderingtremor, creating damage estimated in the

beginning at $2 billion and rising asestimates come in.

Until now, the recently revealedGreendale Fault has been blamed forunleashing the magnitude-7.1 quake onSeptember 4.

GNS Science seismologists workingfulltime on the data recorded since thenthink the second fault may be responsibleand provide the missing piece of thepuzzle.

They say evidence points to a blindthrust fault lying at depth somewhere in abroad northeast to southwest zone centredon the focus of the big quake close toCharing Cross.

They believe that when that faultruptured it sent out shockwaves thatkicked into action the slumberingGreendale Fault slightly further south.

The release of several pulses ofenergy from faults about 4.35am that dayand a foreshock seconds before the mainshake have complicated the picture.

GNS spokesman John Callan said theepicentre was the source of the first pulseof energy.

‘‘There were two main pulses about10 seconds apart, then a third less distinctpulse about 30 to 40 seconds later,’’ hesaid.

‘‘The quake was a result of two faultsrupturing within seconds of each other.The first fault to rupture was a blindthrust fault. It has no surface expression.It triggered the east-west Greendale Fault.

‘‘Fortunately, there wereseismometers at either end of the fault, atGreendale and Rolleston. This has helpedwith the completeness of the seismicrecord.

‘‘This was a highly complex quakethat was exceptionally well-recorded. Thequake will contribute significantly to theunderstanding of earthquake physics andfault mechanics, and therefore it hasglobal implications.’’

Seismologist Bill Fry said there wasstill a lot that was unknown about thesecond hidden fault. ‘‘The GreendaleFault extends down through the upper andmiddle crust to about 10 to 12 kilometres.But the thrust fault – we’re still decidingon the exact location of that.’’

The large quake changed the strainlevels in rocks around the region, he said.‘‘This has created an increase in stressfields in some areas and a decrease inothers.’’

Fry said the areas with the greateststrain were where the aftershocks werelocated.

CHRISTCHURCH SHAKES: 4 September 2010 3

4.36 am Magnitude 7.1 quake hits the South Island. Theepicentre is close to the town of Darfield. Reports ofthe quake being felt from as far away as Dunedin andPalmerston North.

4.38 am Initial reports of quake begin to filter through to Twitterwebsite.

4.56 am First large aftershock strikes: magnitude 5.3 quake ata depth of 8 km, 30km west of Christchurch.Aftershocks continue at through the day.

7.46 am First reports of looting in the central city8.17 am Confirmation that two people have been seriously

injured in the quake9.35 am Civil Defence is warning of the risk of water

shortages, advises people living on the flat inChristchurch to conserve water and boil all drinkingwater.

10 am Christchurch declares a state of local emergency12 pm Prime Minister John Key says he is rushing to

Canterbury to “show solidarity” with locals rocked by amajor earthquake.

12.23 pm Christchurch Police confirm they have closed the citycentre until tomorrow.

12.30 pm MetService issues a severe weather warning for theCanterbury region, warning of severe rain and gales.Temperatures expected to drop to 2˚C overnight.

12.50 pm The cost of damage from the devastating quake couldbe as much as $2 billion, Earthquake Commissionchief executive says. Ian Simpson

1.30 pm Christchurch Airport is operational after the airportrunways and infrastructure were assessed fordamage.

2.10 pm Waimakariri District Council is advising Kaiapoiresidents to leave town if possible, as it may be a longtime before water or sewerage services are restored

2.20 pm Cellular networks in Canterbury are being restored tonormal with both generator and mains power, butusers are still being urged to stay off their cellphonesunless they need to make essential calls.

4.30 pm A building in the CBD on the corner of Worcester andManchester Streets burst into flames but was soonbrought under control.

5 pm Power has been restored to 77% of Christchurch city.But rural areas are largely out of power as a result ofdowned poles or lines

Sunday 5September3.00 pm

Chief Medical Officer of Health advises all publicbuildings, including schools, are to remain closed untilWednesday for safety inspections

Source: Sunday Star Times

The Earth’s crust is divided into plates whichare in constant motion and collision. Theplates; boundaries are called fault lines.Earthquakes are caused by sudden joltsbetween fault lines.

Occurs when plates move away or extend

Occur when plates move alongside oneanother causing friction

Occurs when plates come together/compress

A moment in time: the clock towerin Victoria St stopped at the time ofthe earthquake

Events of the first day■ What causes earthquakes


More than most disasters, anearthquake finds a city out.A severe shake testsinfrastructures, examines

emergency responses, exposes planningdecisions and, most of all, it asks somesearching questions of its people.

Canterbury, in its first week after themajor tremor, which struck at 4.35am onSeptember 4, has passed many of thesetests with flying colours. It should giveitself a collective pat on the back - but nottoo hard.

A week after one of the biggest joltsto strike, a modern, populated cityanywhere in the world, Canterburyauthorities have managed to restore mostof the services usually taken for granted.

By tomorrow, just about everybodystill living in their own home inCanterbury should have water and power.Given the extent of the original breakagesand outages, that is some achievement. Infact, most homes had water and power byMonday night, and by Tuesday 90 percent of the city’s residents were able toflush their toilets. By yesterday, only 11streets were without water. Theairport inspected its runwaysimmediately and within hours, aircraftwere taking off again. The Port ofLyttelton was working again on Sundayafternoon despite up to $50 milliondamage to wharves mid storage areas.

As expected, Canterbury peoplepitched in and did what they could forthemselves and their neighbours andfriends. The welfare centres set up onSaturday were still busy mid-week withabout 280 people in occupation. But outof the city of 360,000 or so, that is not alarge number.

People like bungy king A J Hackettwent ahead with their weddings in theruined city. Mike Bird didn’t have muchchoice. He had already tattooedSeptember 4 on his arm.

By Wednesday, the chooks hadstarted laying again and by Thursday,several schools had reopened. Not all thememories were bad. A few hours afterthe quake. writer Joe Bennett foundeveryone in good spirits. “Everyone, wastalking in the sunshine. There was a lot oflaughter. It didn’t seem to be the nervouslaughter of survivors. It was cheerful,convivial. It felt like a holiday,” he wrote.

In the aftermath, Wayne Alexander,of Christchurch, said: “You’re nevermore in love with life and that’s what Ilike about it. Whenever you face loss,you realise on the other side of it whatyou’ve got.”

But first there was terror. For many,the noise was deafening as windowsrattled fit to break, glass and crockerycrashed to the floor and chimneys andtiles toppled. For many in the beach

suburbs, the first panickedthought was for a possibletsunami. Those who had accessto their vehicles caused a trafficjam as they headed away fromthe coast. Without power, manycould not open their automaticgarage doors.

Annette Preen, living on herown in her new house inBexley, felt trapped as she triedto kick down her security door.“I thought I was going to die.”When she made it outside, shefell headfirst into the wet sandpiled at her front door.

“I fell flat on my face andthe silt being so heavy, 1couldn’t get out.”

For Chris Piper, 18, of StMartins, it was the scariestmoment of his life. He wassleeping in a sleepout behind

his family’s home and was wokenpainfully when a television fell on hisfeet.

“I threw my girlfriend on the lawnand then went to the house in bare feetand my underwear to see tiles and thechimney crashing down. I thought thewhole house was going to collapse. 1thought my whole family was going todie in front of me.”

Imagine the plight of paraplegicRenee Hayman, lying in her room at theKate Sheppard Hospital in Avonside. “Ifelt quite helpless, really.”

At dawn, Christchurch turned on apearler of a day. Residents could surveythe damage in the light of warm brightsunshine. Another godsend, perhaps.

Supermarkets were some of the firstbusinesses to re-open. By 10.40am, StMartins New World had cleaned up aislessmelling of vinegar and alcohol and hadtills running on generator power. Bymidday, power was on again and businesswas as busy as a Christmas Eve, ownerRussell McKenzie said.

Other supermarkets around town dealtwith panic buying and were soon out ofbottled water, milk, bread, batteries andcandles. As it became clear starvationwas going to be averted, the panicsubsided. Frantic buying at the city’sservice stations also abated as it becameclear fuel supplies were not threatened.

Riccarton High School, like others in the region, was closed for a week to check the safety ofbuildings, water and sewerage

A week of the shakes

■ The Press, Saturday, 11 September 2010


Christchurch remained off limitsto an estimated 50,000 workerswith police and army cordonsin place around the central

business district. A state of emergencywas extended, and until buildings werecleared by structural engineers, staffneeded to keep clear.

A series of aftershocks compoundedthe problem as they often furtherdamaged buildings that had been clearedfollowing the initial earthquake.

Damage occurred in many suburbs,with some residents moving away to staywith friends or relatives, or in temporaryaccommodation; yet other areas wererelatively unscathed.

Apart from obvious structural damage(at least one Canterbury house in ninehas chimney damage) there have beenother effects. Liquefaction occurred inmany suburbs, such as Avonside andBexley Park, in East Christchurch.

When sandy soil is jolted hard by the

earthquake, it changes its structure andfalls apart. In this case water bubbled upthrough cracks in concrete like springs,bringing black silty soil with it thatcovered driveways with the consistencyof heavy jelly.

Where the water and silt was trappedunder concrete, paths and roads werepushed upward, tilting and breakinghomes and creating mounds on roads andpaths. The tarseal crust on many of theseroads consequently broke into rubble.

The effects of the Quake

Damage in various parts of Christchurch

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The sea arch as it was in Sleepy Bay, top, and how it is now, after itcollapsed, having been weakened and damaged by the September 4earthquake

Going, going, gone. ACanterbury landmark has beendestroyed by the earthquake.

The sea arch in Sleepy Bayon Banks Peninsula partiallycollapsed during the Septem-ber 4 earthquake and the re-mainder fell into the sea morethan a week ago.

The stone arch was a fea-ture on peninsula walks and afun challenge for kayakers.

It was also the restingplace for the ashes of membersof the Narbey family whohave farmed the area since1850.

Brian Narbey was muster-ing sheep 9 days ago when heheard the remainder of thearch, known as the mirror orthe spyglass, fall into the sea.

“It was a big rumbling as itwent down into the sea,” hesaid. “It’s a local landmark.There must be thousands ofphotographs taken of it. It hasbeen there forever and now ithas gone. It’s sad to see it go.It is a new era.”

Banks Peninsula residentand writer Fiona Farrell, whotook these photographs, alsosaid it was sad to see it go.

“It is quite an absence. Itfeels quite strange,” she said.

The arch was also used asa location for Hollywoodblockbuster Underworld: Riseof the Lycans.

A miniature ship wasfilmed floating through thearch, with the footage used inthe film’s closing moments.

Sea arch tumblesinto sea

Physicalimpacts

The Press, 4 October 2010

The movement of the land is shown by the shift of the shelter belt on afault trace between Greendale and Burnham

Huge craters in Kaiapoi caused by the earthquake, large enough towalk in


Liquefaction

Large tracts of silty, low-lyingland in Canterbury weretransformed from firm land tosludge. In what’s known asliquefaction, Christchurch’s

sandy soil was shaken violently, causingwater to rise through its pores. Scientistscompared it to jumping on wet sand atthe beach,it soon turns to a murky soup.

Professor Michael Pender fromAuckland University’s geologydepartment said the Canterbury quakewas one of the most significant cases ofliquefaction in New Zealand history, butthe process could affect any town or citynear a river, estuary or coastline.

Large sections of Christchurch werebuilt on soft sediments which remainedsaturated after a wet winter. Roads,bridges and pipe infrastructure have beenunsettled by the water squirting upthrough the soil during the 7.1 magnitudetremor.

As many as 9 out of 10 homes on thecity’s flat have been damaged by the

quicksand-like effect. Much of thisdamage was superficial rather thanstructural. But in Bexley, a 5-year-oldsubdivision, at least 100 new homes wereleft uninhabitable after silt, sewage andgrey sludge cracked the road andsqueezed through floorboards.

The worst-affected areas were coastalspots such as New Brighton, and suburbsthat skirted the lower reaches of the Avonand Heathcote Rivers, in particularDallington.

Homes in Kaiapoi, near theWaimakariri River, were also reported tohave sunk into the soil.

Geologists said when rising water wasconcentrated into small cracks it couldcreate sand volcanoes — mounds of sandthat pushed up to the surface, as seen onthe streets of Avonside and Linwood.

Professor Pender was surprised thatsome new developments suffered majordamage from underground water.

‘‘You’d expect the engineers doingthe site investigation to realise that there

is this loose sand present and do someremedial work before they builtfoundations.’’

■New Zealand Herald, 7 September 2010

When the ground shakes during an earthquakethe soil particles are rearranged and the soilmass compacts and decreases in volume. Thisdecrease in volume causes water to be ejected tothe ground surface

Liquefaction happens during earthquakes. Theground shaking that occurs can cause someto liquefy.

Sand volcanoes or sand boils, water fountainsand associatd ground surface cracking areevidence that liquefaction has occurred

Sand volcanoes, indicating liquefaction

Liquefaction riskin Christchurch


Manchester Courts, Manchester and HerefordStreets corner, a heritage building, was built in1906. At 7 storeys, it was at one time thetallest commercial building in Christchurch. Itwill be demolished.

St John’s Church, Hororata suffered severe damage

Cracks in St Elmo Courts in Hereford St. It mayhave to come down due to costs of rebuildingto new earthquake standards

Impact on structures

Bridge over the Avon River at Avonside

Some of the older buildings builtbefore earthquake building codes were inplace have been affected badly. Many areheritage buildings and add history to thecity, but they may have to be demolished

as the cost of replacing them may be tooexpensive.

The fact that many modern buildingswere largely unaffected shows that NewZealand’s building codes are strong.

“Modern buildings are designed tobend like a piece of wire rather thanbreaking like a stick,” the director of thecity’s largest structural and civil engi-neering firm, Holmes Consulting Group,says.

While attention has focused on thedamage to the city’s older buildings andprivate homes. the effect on the city’smodern commercial buildings was lessdramatic but nevertheless holds impor-tant lessons for the future.

“Essentially, earthquake design inNew Zealand began in 1965. In 1976, itwas brought into the modern era withresearch at the University of Canterburywith an approach which concentrated onsaving lives. Buildings would fail but in avery controlled way,” Hare says.

“There was an acceptance and grow-ing realisation that you couldn’t makebuilding indefinitely stronger becausethere would always be a stronger earth-quake. It would be impractical to simplybuild extremely strong buildings - theymust also have the ability to yield, flexand move in an earthquake. Many, butnot all, of Christchurch’s taller buildingshave been designed in this way and mosthandled the earthquake well.”

The 1929 Murchison and the 1931Hawke’s Bay earthquakes profoundlyshaped New Zealand’s perception of thehazards of living in a seismically activeenvironment.

Attention was focused on weaknessesin building construction, especially poorbuilding standards and the lack of anyprovision for earthquake-resistant design.

This led to a draft by-law in 1931,which was incorporated into a buildingcode in 1935. Building codes in 1965,1976, 1984 and 1992 have added require-ments to accommodate changes in build-ing materials and design. Rather thanprescribing specific materials, designs orconstruction methods, the 1992 NewZealand code outlines how a buildingmust perform to withstand the forces ex-pected during an earthquake.

This allows builders to use innovativedesign and construction methods to cre-ate earthquake-resistant buildings. For amoderate earthquake, the main aim is toprotect a building from structural dam-age. For a major earthquake, however,the goal is to protect life by ensuring abuilding will not collapse and people canescape from it, even if the building itselfis badly damaged.

Seismic lessonsThe Press, 16 October 2010


Economic impact

HOUSEHOLDS: HOUSING� Over 93,000 claims made to

EQC� about 5000 houses have

damage costing more than$100,000

� 17,000 claims for chimneydamage, almost half of whichwhere the chimney is the only

HOUSEHOLDS : INCOMES� damage to buildings/premises so

some employees had access totheir place of employment.

� Government’s EarthquakeSupport Subsidy, for businesseswith fewer than 20 staff, paid thewages of staff while firms gotoperational again

BUSINESSES : ASSETS� Some 50 buildings were declared

unsafe� cost of repairing wharves at the

Port of Lyttelton� large-scale loss of goods, such

as warehousing of foodstuffs

BUSINESSES: INCOME� loss of production and sales

through damaged buildings

LOCAL GOVERNMENTS� damage to public infrastructure:

roading, sewerage and drainage

CENTRAL GOVERNMENT� damage to schools and hospitals� Loss of taxation� Payment of benefits

An Indian dairyowner whosefamily lived abovehis business is

without a home and incomeafter his quake damagedbuilding was condemned.

Ferry Rd Mini Marketowner Hemant Shah was justone example given to EthnicAffairs Minister Pansy Wongof the plight of Christchurch’sethnic communities yesterday.

Shah’s dairy suffered onlyminor damage, but the flat heshared with his wife and twochildren above the shop hasbeen given a red “no-go”sticker.

The family has beenbarred not only from theirhome, but also from theirbusiness. Shah’s wife andchildren were living, separat-ed, with various friends and amiscommunication at Workand Income meant he was ini-tially told he was entitled toonly a $113 benefit.

Shah had contentsinsurance, but no incomeprotection.

Community leader NatuRama called on the Govern-ment to provide guarantees tosmall business owners, partic-ularly around insurance.

Hardeep Singh, a friend ofRama and a restaurant owner,had just taken the lease on anumber of premises in theFerrymead area, but had beenunable to open because he hadbeen given a 21-daystanddown by his insurancecompany, Rama said.

The Government neededto act “to alleviate the pain inthe short term”. He suggestedan interim guarantee wouldallow business owners to getback on their feet.

Wong said she wouldconsider the insurance issue.

Language difficulties hadbecome an issue because “in astress situation the mothertongue sets in”.

The Treasury estimates that the Canterbury earthquake will costabout $4 billion. This is made up of many items, most of whichare shown in the panels below. Over the next few years, theregion will get a boost economically as people begin to replace

items they have lost (eg. houses, furniture, TVs) and both localand central governments rebuild their facilities such as roads,drainage, schools and so on. This increased economic activitywill give a boost to the local region compared to other areas.

Costs of the Quake

Many small businesses could not open because of the damages

The Press, 11 September 2010

Loss of businessand home


Impact on peopleThe physical effects of an earthquake are dramatic and frightening. Also traumatic is the impact upon the lives of ordinary people —families, children, the sick and the elderly. Some of the effects will linger for months; maybe even years. Study the situations listed ineach box and explain the complications.


Immediately following a earthquake assistance is first sought from families and neighbours, followed by emergency services.After that it is the turn of central government, local governments and relief agencies. The following is a list of someorganisations that helped.

A helping hand

Insurance Council

Recovery Assistance Centres

Victim Support

Canterbury Earthquake Commission

Age Concern Home visits*

*Christchuch City Council

Some of the thousands of students helping local residents cleanup their properties

Natural disasters can sometimes bring out the best in people. Itis a healthy neighbourhood where members experience a majordisaster, yet manage to look after each other throughout. It isalso a healthy society that picks itself up, dusts itself off andplans to make improvements in case sometime like it happensagain


The crust of the Earth is made ofseveral plates, large areas ofsolidified rock which float on alayer, called the mantle, above

the Earth’s core.The mantle begins about 10 km

below the oceanic crust and about 30 kmbelow the continental crust and makes upnearly 80 % of the Earth’s total volume.

As these plates are free to slowlymove, they can either drift towards eachother, away from each other or slide pasteach other.

Many of the earthquakes which wefeel are located in the areas where plates

collide or try to slide past each other.Because the earth is very hot inside, a

current of heat flows from the core to thecrust. This is called convection currentand it also takes place in the mantle. Thiscurrent cools down as it comes closer tothe surface of the Earth.

As a result, the rising of the currentdecreases and goes into a horizontaldirection along the bottom of the crust.When the current cools down more, theconvection current descends again andgoes to the inner Earth. There thetemperature increases and the currentrises again. This goes on and on.

When the current comes to a weakerpart of the crust, such as at a volcano,magma comes above the Earth’s surface.The convection current along the bottomof the crust causes the tectonic plates tomove. This is called plate tectonics.

The movement of these plates is veryslow. The bumping of two tectonic platescauses an earthquake.

There are many fault-lines in theEarth's crust. The typical rate ofmovement is around a millimetre a year.Rocks tend to stick so that over a periodof centuries they reach a critical leveland everything gives at once.

What are earthquakes?

1. Rift valleyContinental plates pull apartallowing crust to sink.

2. Mountain buildingContinental plates collide forcingrock layers to fold and pile upinto mountain ranges.

3. Volcanic islandsSpreading ocean floor is muchthinner than continental platesbut can break the sea surfaceforming volcanic islands.

4. Sea floor spreadingBasaltic magma rises to formnew ocean floor along a fault. Anundersea ridge is formed whichgradually spreads as newmaterial pushes it along its wayaccompanied by almost constantearthquake activity.

Movement of tectonic plates isthought to be driven by sluggishheat currents within the mantle

Mantle currents

5. SubductionOcean floor is forced undercontinental crust and into themagma where it is consumedand recycled. The subductionprocess is accompanied by theworld’s strongest quakes,measuring up to 8.9 on theRichter Scale, which can heavethe ocean floor by many metres.

6. Strike-slip faultsForm where two plates shearpast each other. The resultingearthquakes are less powerfulthan those in the subductionzones but can be moredestructive to people because oftheir focus nearer the surface. Semi-molton

mantle

Subduction zone Spreading zone Thrust fault Strike-slip faultUncertain/diffuse boundary

The surface of the Earth is divided into seven major plates and severalminor ones. They move a few centimetres a year riding on semi-moltenlayers of rock underneath the crust. As the plates move they pull apart orcollide, unleashing the powerful movements known as earthquakes.


New Zealand has oftenbeen called the “ShakyIsles”. The term hasbeen derived from New

Zealand’s frequent seismicactivity. The islands lie on themargin of two colliding tectonicplates, the Pacific and Indo-Australian Plates.

Earthquakes are common,particularly in the southwest of theSouth Island and in the centralNorth Island, and the NorthIsland’s scenery is marked byseveral active and dormantvolcanic cones. The recentCanterbury earthquake occurredalong faults not previouslydetected; however the region isprone to seismic events because ofits proximity to establishedfaultlines.

With seismologists recordingup to 15,000 earthquakes a year,New Zealand deserves itsreputation as the “Shaky Isles,” butmost are too small to be felt by thecountry's 4.3 million people.

Up to 150, however, are largeenough to register, and everyschoolchild is drilled on how toreact to an earthquake - get underyour desk or in a doorway whenyou feel a tremor and taught theneed to prepare for the “Big One.”

Being centred in an areaseismologists had not identified asquake-prone, the Canterbury shakeshowed that nowhere in thecountry was safe from adevastating tremor.

The epicentre of Canterbury’squake was some distance from the

Alpine Fault, which runs about 600kilometres up the spine of theSouth Island and is the boundary oftwo massive geological plates thatare constantly grinding againsteach other.

Seismologists said it hasruptured four times in the past 900years, each time producing anearthquake of about magnitude 8,lifting the Southern Alps in theprocess and producing some ofNew Zealand's most spectacularscenery.

Scientists predicted a “highprobability” that it would produceone of the biggest earthquakessince Europeans settled in NewZealand.

Wellington, which has fivemajor fault lines, has long beenregarded as the most likely toexperience the Big One.

Seismologists said the so-calledWellington fault, which lastproduced a quake of aboutmagnitude 7.6 300 to 500 yearsago, would spawn another insidethe next 200 years.

As 20 aftershocks ranging from3.9 to 5.2 on the Richter scale wererecorded in about 15 hours afterthe early morning shock inCanterbury, it was impossible topredict whether another Big Onewould hit Christchurch.

But records showed that Napierwas struck by a massive aftershockmeasuring 7.3 10 days after thecity was levelled 89 years ago.

It is all a bit unpredictable, andshocking when it occurs in a placewhere it was not expected.

New Zealandin the firing

line

Ash clouds from Ruapehu eruption, 1995, disrupted flights

Napier earthquake, 1931, measured 7.8 on the Richter Scale


Left side of the chart shows the magnitude of the earthquake and rightside represents the amount of high explosive required to produce theenergy released by the earthquake. The middle of the chart shows therelative frequencies.

Krakatoa volcanic eruption

World’s largest nuclear test (USSR)Mount St Helens eruption

Hiroshima atomic bomb

Average tornado

Large lightning bolt

Moderate lightning bolt

475 megatonnes

15 megatonnes

475 kilotonnes

15 kilotonnes

475 tonnes

15 tonnes

475 kg

15 kg

(equivalent of explosive underground)15 gigatonnes

7.1 InangahuaMay 24, 19687.1 ChristchurchSeptember 4, 2010

February 3, 19317.8 Napier

June 17. 19297.8 Murchison

March 27, 19649.2 Alaska

February 27, 20108.8 Chile

Power of earthquakes

How to read the Richter Scale, the best known scale for measuring the magnitude of earthquakes

� Conspicuous cracks in ground� Masonry and wood structures

seriously damaged� Danger of large landslides

� People have difficulty standing,steering vehicles

� Chimneys, stucco and masonrywalls crack

� Pipes break, danger of fire� Masonry and wood structures

seriously damaged

� Everyone feels the quake� Houses shake, glass breaks,

furniture slides, objects fall

Amount of damage also depends on how close the quake is toa city and how well the community is built

Christchurch shakes : 4 September 2010 booklet.pdf · shake have complicated the ... The Earth’s crust is divided into plates ... boundaries are called fault lines. Earthquakes

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