Darfield earthquake, New Zealand

2010 Sept 04 04:36 NZST - magnitude 7.1
Christchurch NZ was shaken and battered by this magnitude 7.1 earthquake but no one was killed despite extensive damage to low rise URM buildings and to infrastructure, not unlike that experienced in Newcastle NSW in 1989. There is widespread ground failure, liquefaction and lateral spreading, which has caused dramatic damage to houses and underground sewer and water pipes. High rise buildings were apparently undamaged. Bridges suffered settlement of abutments. Power substations throughout the area were virtually undamaged. An east-west trending surface fault, right lateral strike-slip and about 23km long, has been mapped by GNS.

AEES Committee members Mike Griffith and Kevin McCue travelled to New Zealand to learn from this earthquake.

Professor Mike Griffith arrived in Auckland on Saturday afternoon 4th September, the day of the earthquake and travelled to Christchurch the next day with colleague Jason Ingham. Mike's report is attached below.

The GeoNet NZ website describes the GNS response to this earthquake. GNS Science has a new page summarising the Darfield earthquake and subsequent response. You can get further technical details from here. We highly recommend viewing the fault trace flyover video on YouTube that GNS Science has put together.

The NZ Society for Earthquake Engineering has established an official electronic clearing house for earthquake information. The link can be found on their home page.

Image Gallery

24 hours of aftershocks recorded on a seismograph near Christchurch	Managing the response (l2r Peter Wood President NZSEE, Russ van Dissen paleoseismologist, Kelvin Berryman science response coordinator)		Liquefaction damage, Kaiapoi	Badly damaged Church near western end of surface fault, note broken-off headstones	A Childrens Science Centre, formerly a railway station. Cracks in the tower show interaction with 3 storey abutting building. Note the clocked stopped at the time of the earthquake	Pavers used to form a straight path	Liquefaction and subsequent settlement damage, Kaiapoi
Reinforced heritage URM building Christchurch - undamaged	Electricity substation near surface trace of fault - no damage	Damaged but business as usual for this Christchurch city printer (printed the NZSEE Bulletin the day before the earthquake)	Heritage pub near Lyttelton Tunnel entrance, east of Christchurch	Sand volcano, Kaiapoi	Liquefaction damage, Kaiapoi	New Dogleg in Road	Water channel Offset

Notes from Christchurch - Mike Griffith, University of Adelaide
8am, Saturday morning Adelaide (4/9/10)
Heard radio broadcast of earthquake in Christchurch, NZ. After seeing TV news reports of damage to unreinforced masonry buildings I booked flight leaving 11.40am for Auckland. Met by Jason Ingham (Univ of Auckland) at 10pm.

6.30am, Sunday morning (5/9/10)
Flight to Christchurch for 9am briefing at Command Centre (Christchurch City Council (CCC) Art Centre building). David Brunsdon (NZSEE) was advising CCC and coordinating rapid building assessment activity for CCC.
9.30am – 2.00pm
Received assignment from CCC. Was assigned to assessment team (USAR technician, local structural engineer, two CCC building officials and myself) to conduct Level 2 assessment of Manchester Court, a 7-storey building on the SE corner of Manchester and Hereford street intersection with the upper 5 stories having load bearing unreinforced masonry piers around the two street front walls of the building. The masonry piers were badly cracked at levels 3 and 4. Local police and fire brigade assisted team with entry to building and offices inside. Inside plasterboard was stripped from piers to confirm that cracking went through the entire pier and that there was no internal reinforcement in the piers. The team gave the building a yellow tag with Y2 rating which means ‘no entry until parts repaired or demolished’. The building was subsequently given a red tag late on Sunday. I met USAR team leaders and engineers and city officials on Monday morning at 7.30am to discuss strategies for making the building safe enough for building contractors to carry out further work – either demolition or repair, a decision that at that time had not yet been made. For more details see the NZSEE website
2.00pm – 5.30pm - after returning to Command Centre the team was assigned Cashel Street buildings between Oxford Terrace (west end) and Madras Street (east end). All buildings were tagged along both sides of street by the team. Most buildings with observable damage from the exterior were unreinforced masonry (URM) buildings, or buildings adjacent to URM that suffered collateral damage such as parapet or chimney falling through roof. Almost every failure observed was some form of out-of-plane failure mechanism. More details are available at the NZSEE website

8.30am – 5.00pm, Monday (6/9/10)
After briefing at Command Centre was assigned to assessment team for all buildings on Tuam and St Asaph Streets in SE corner of CBD. Aim was to confirm rating of previous tagging and downgrade where possible after more detailed inspection. Key objective on ‘day 2’ was to mark where fencing barricades were needed to keep the public safe from falling hazards when the cordoned section of the city was reduced or removed. We experience three M5.4 aftershocks during the night at our motel.

8.30am – 5.00pm, Tuesday (7/9/10)
After briefing at Command Centre, met briefly with USAR team leaders and technicians to plan strengthening scheme for Manchester Court building. Other assessment teams were sent out to revisit all buildings to determine whether the current tag was needed to be upgraded due to the large aftershocks. For the afternoon I worked with Jason and a number of his PhD students to document damage to masonry buildings in the western side of the CBD before he left to return to Auckland.

8.00am – 1.30pm, Wednesday (8/9/10)
Experienced a M5.1 aftershock in café on way to Command Centre – pictures fell off walls and broken glass in café and parapets falling off hotel building across road! Brief ‘exit interviews’ with David Brunsdon (NZSEE) at Command Centre and Des Bull (NZ USAR). Stabilisation work at Manchester Court building stopped due to safety concerns for USAR technicians. Unfortunately, I had to leave before any resolution was found for the next step for this building. Very glad to be back on ‘solid ground’.

Final Comments
The experience as a structural engineering to help with building assessments in the initial ‘response phase’ of the disaster was extremely rewarding and educational. I think I can speak for Jason too and say that we feel that we really helped and that Christchurch officials were genuinely thankful for our help. I strongly encourage other structural/earthquake engineers to take the opportunity when it occurs in future. My observation was that the main focus for the first 72 hours was ‘rapid response and building evaluation’. At the end of day 3 it became clear that the responsibility was shifting on to locals (engineers and building contractors) to engage with the owners of buildings to make decisions about repair and/or demolition, depending on the ‘tag’ for their building. This is clearly work that will occur over the longer term. Hence, Jason and I felt quite comfortable in our decisions to leave when we did. As for scientific studies, I am sure that there would be benefit in further visits to document that extent of damage, especially as the greater Christchurch region has not received the attention that the CBD has. However, the cleanup of the city is well underway and I suspect that it will rapidly become difficult to see the full extent of damage to buildings in the city centre.

Acknowledgements
A big thanks to Jason Ingham at the University of Auckland for meeting me at the airport in Auckland, putting me up the first night, getting me to Christchurch and providing our accommodation there. Quincy Ma from the University of Auckland also provided logistical assistance for which I am grateful. Jason’s PhD students also did much of the photography for us as we were occupied with the documentation associated with building assessments. Finally, I want to thank the AEES for covering the cost of my airfare.

Notes from Christchurch - Kevin McCue, AEES President
Thursday 9th September
Arrived Christchurch motel on the northeastern edge of the city at 1:15 am. The morning stroll into the Environment Canterbury Regional Civil Defence Office at 08:30 wasn’t straightforward as Victoria Rd was blocked in several places due to demolition work in progress. Yes it has started already, just as in Newcastle in 1989 there is strong pressure to get the city back to BAU, Business as Usual! But there was surprisingly little obvious damage on route. I camped in Dr Kelvin Berryman’s small campaign office till lunchtime, Kelvin is organising the scientific response to the Christchurch2010 earthquake with support from Bronwyn Davies, it wasn’t pandemonium only because of their graciousness under extreme pressure. People came and went all morning, the phone was constantly ringing and Hannah organised accelerograph installers from the third corner.
Professor John Berrill from the University of Canterbury had fortuitously installed a network of his in-house-built accelerographs around the Christchurch area as an array to capture any Alpine Fault earthquake but they hit the jackpot with a magnitude 7 intraplate event instead. In addition there were GNS national network stations in the area.
A magnitude 7 earthquake is included in the background source for the NZ PSHA so this was about the 500 year design earthquake and no change is expected in the hazard map as a result of this event. The good thing was that no one was killed (one person died of a heart attack). The NZ Loading Code required that engineers and architects accommodate a Z factor of 0.22 (Z akin to pga) in their building design and they must have because there were no catastrophic failures and no loss of life, despite the average pga recorded throughout the city of about 0.2g. Kelvin pulled out a map of the liquefaction potential under Christchurch with four zones high to zero and contours of depth to watertable. It was published in 1992. There was extensive liquefaction, most of it sand and water pumped to the surface from only 1 or 2 metres down, most of it in the high hazard region. The Canterbury Plain is a wedge of glacial outwash, gravels some limestone, approx 1 km deep, thickening to the east with a thin veneer of recent confined, saturated, sands.
Stanford University shipped out 200 simple accelerographs ($27US each), which are being deployed around the city to supplement a generous existing network (see the Geonet website). Each accelerograph requires a broadband internet connection via a usb port through which they download triggered data back to Stanford (shared of course).
In between the phone calls and visitors we discussed the earthquake, the data and the geotechnical challenges.
Just before lunch I walked down to the local Christchurch Arts Centre converted into the local disaster response centre, most of the officials sporting multi-coloured identity vests and soldiers in uniform controlled entry and exits. Andrew King was on his way to a meeting of the Economic Recovery Taskforce so I joined him. The meeting covered a wide range of issues including government support for loss of business, support for people suffering psychological stress to whether infrastructure support should be restored in high risk liquefaction zones ie what is the acceptable risk and who should determine it.
Later Andrew, Graham and I drove through suburbs along the River Avon to inspect damage and the effects of liquefaction, road disruption, closed bridges and building settlement to 0.5m. Building damage appeared to be minimal from a street inspection (just like Newcastle) and there were striking examples of 1.5m tall old URM chimneys still standing, some in splints, though many others were down. The rows of porta-loos indicated were sewerage lines were broken with many excavators hard at work effecting repairs. Sandpiles lined the streets, dumped there by residents cleaning up the vented sand from their blocks. It rained gently all afternoon.
At 5pm we attended a meeting back at the Environment Canterbury Regional Civil Defence Office chaired by Dr Bruce Dean where the various science and engineering groups had a very useful debriefing meeting though the geotechnical group hived off for a separate meeting. Some buildings apparently suffered considerable internal stress though not obvious from a casual inspection outside. Bruce announced that NZSEE was establishing a contact centre for overseas visitors who were expected in numbers (~50) next week.
A long busy day was capped off over a very pleasant diner with Kelvin, Andrew, Graham McVerry and John Zhao discussing the earthquake. At 12:25am I felt my first aftershock, a gentle rocking of the bed, a window rattled softly, just a few seconds and then it was over.

Friday 10th September
Dr John Zhao GNS engineering seismologist, picked me up at my motel at 08:30 for a site visit to several of the accelerographs. It was raining lightly. Our goal was to examine the sites of anomalous records to identify an obvious cause for the unusual records. On route we collected Prof David Mukai, structural engineer from Uni of Wyoming on sabbatical in Christchurch.
We visited several accelerographs, near Lyttleton where an 1860’s vintage URM heritage pub was being demolished, another in a school at Rolleston and then the Greendale instrument in the garage of a converted wooden church, about 1 km from the fault. Almost no structural damage in the church yet the barbeque was turned upside down, a heavy concrete roller moved back and forth a metre or so, a full 2000l water tank moved 15 cm on its 1.5m high steel stand and the contents of the house and garage were trashed.
We examined an electrical transformer station nearby which continued functioning though undermined by a right lateral segment of the fault; fences, roads, drainage channel all offset by 1.5m. A pity the road cracks had been repaired (obliterated) already, though offset fences and power poles told the story. An adjacent recently built farmhouse on a concrete slab was not so lucky and will have to be demolished, the tenants gave us access to photograph the considerable internal damage. A helicopter and small plane buzzing overhead were obviously filming or doing the promised LIDAR monitoring.
On the way we stopped to photograph building damage, especially masonry buildings. David lectures in masonry construction in Wyoming and pointed out the extreme vertical irregularity of a 6 storey child’s science museum which was badly cracked, roped off and yellow-carded.
We returned too late to attend the 6pm briefing meeting, which was regrettable, but the trip was very useful. GNS /Geonet have amassed a very extensive dataset to guide future research and upgrade of loading codes. John showed us some of the time series he had carefully analysed, the Greendale record showing a permanent displacement of about 2m consistent with on-ground observations and pga well in excess of 1g. We are questioning the origin of the large spikes in the horizontal components and suggest a sturdy metal cage be fitted over instruments in storerooms or garages.
Felt another small gentle aftershock about 10 pm as I was sitting writing my report.

Saturday 11th September
Dr John Zhao GNS engineering seismologist and I departed at 08:30 to visit some of the accelerograph sites and inspect buildings in the mapped fault region to compare the recordings with observations of damage. Despite the forecast it was not raining. Our first stop was Greendale which we had visited the previous day, max pga 1.25g, max pgv ~ 1.2m/s and displacement >1.5m.
Inspection of the recorder showed that a length of timber had jammed horizontally between the garage frame and the recorder box which might explain the odd pulses on the record. Despite the strong ground shaking, there was no structural damage to the house or garage but three galvanised steel restraining straps on the new 225l hot-water tank had failed, the house contents were trashed and the couple could not physically get out of bed until the shaking eased. They did not hear the crockery, glassware and bottles smashing in the next room over the pulsed roaring of the earthquake. Undoubtedly the shaking was strong and lasted for more than 10 seconds but there was no structural damage in the 100 yr old timber former church or 1960s vintage adjoining hall and the lead light windows were undamaged apart from all the ties to the horizontal steel restraining rods being broken.
From there we visited a local school and found the accelerograph in a tool shed and there were no obvious problems with the instrument though the school doors were wide open and there was a strong smell of gas. One school building was taped off with a warning of a gas leak and the 2000l plastic water tank had physically moved about 5 cms from its normal rest position in the ground.
Our next stop was Hororata where we saw our first red-tagged building, the local pub, and a 100 yr old basalt block church which had lost part of its steeple, roof and walls, and was trashed internally, the organ a heap of twisted pipes, stone work and roofing on the nave floor. Several headstones in the cemetery, perhaps one in twenty were broken off or pinned in place. The good news is that this church will be repaired. Other buildings in town suffered some damage, power poles were leaning at odd angles and an elevated water tank was on the point of toppling with no evidence of liquefaction. Interesting observations from the locals included that damage increased in the days following the earthquake, the western growth of the fault trace features, windows left unbroken after the earthquake did break in the next few days, wide cracks in walls appeared where there were none before and stream flows appeared to significantly increase though rainfall was light.
On our way back to Christchurch to attend the daily briefing meeting we stopped again where en echelon secondary faulting segments intersected the road. Several damaged masonry buildings in the city have been reduced to piles of rubbish, presumably in case they fell out into the streets. Some streets are still partly blocked, the northern end of Victoria street is still cordoned off.
The main meeting room was full (40+) when we arrived shortly after 6pm. Peter Wood was talking about the various emergency management groups and the wiki through which data would be exchanged. He said the basic mapping by LIDAR at 1m spacing and aerial photography was complete. A bare earth model from LIDAR has been produced. Kelvin Berryman who was coordinating the meeting then asked for brief reports from each of the disciplines. It seems that many of the liquefaction features seen around the city coincide with sewer and water pipe trenches. Plans are afoot to trench some of the large liquefaction features in Kaiapoi. Lateral spreading was limited spatially, much more damage attributed to liquefaction. Building inspections are basically completed, especially of masonry buildings and problem housing. Not enough undamaged buildings and commercial high rise buildings have been inspected though there appears to have been no significant damage to the latter.
Near coast settlement may have reduced flood protection in places by up to 50%. John Zhou stressed the need to be careful using the strong motion data until it had been checked (data on the Geonet website has been filtered, and anomalies such as spikes not yet removed).
Urgent need to report on settlement and liquefaction as parliament will be making decisions soon about restoration versus relocation. Arranged to have dinner with Peter and John, geologists and the geotechnical team, a dozen of us altogether plus Kelvin. A long day.

Sunday 12th September
A small aftershock at 6am brought me fully awake, the sliding bathroom door gently bumping the kickboard. Met up with Peter Wood for breakfast at 7:30 to talk about PCEE2011 and the Southwest Pacific Islands hazards workshop.
John Zhao joined us at about 9am and then he and I left for Kaiapoi to inspect the liquefaction features and their effects.
It was very sobering to drive the streets of Kaiapoi about 40 minutes drive north of Christchurch. There was fine grey volcanic sand everywhere and mini grabens through gardens, roads and under houses due to lateral spreading and liquefaction. At one house the wheel of a wheelbarrow could be seen protruding from the bottom of a metre deep trench. In another all but 30 cm of a 3m long ladder was exposed. Obviously the liquefied sand extended down at least 2m.
Many houses, all built on integrated concrete rafts because of the sand, were broken and leaning at crazy angles. Some houses looked ok on first sight but then we noticed that a quadrant of turf had been removed from the lawn so that a door could be opened.
Water and sewerage lines were fractured and Porta loos dotted the streets, raw sewerage was being pumped straight into the river and thence into the sea.
A footbridge was folded dramatically due to lateral spreading of the banks and the parallel road bridge recently reopened, though services through the bridge were seriously compromised.
We returned to Christchurch at 5pm to attend a briefing for incoming visitors from the US, Japan and GA and chaired by Kelvin Berryman and Peter Wood. There are about 150 scientists and engineers in the area, not counting the building safety reconnaissance teams. It looks as though the state of emergency will be lifted soon, perhaps as early as Wednesday.
A magnitude 4.6 aftershock shook our meeting venue at about 5:26 pm but no one turned a hair.
The NZ Civil Defence Controller, Bob Upton reported that there were no deaths, 2 serious injuries and 380 displaced persons. The ‘traffic light’ assessment system of building marking had yielded 80% green, 14% yellow and just 6% red. Amazing given the ground motions. Not one building collapsed.
The Canterbury Council had recently reviewed their earthquake-prone building policy and upgraded the requirement to 67% of new buildings design levels from just 33% ie reduced the risk of damage from 10 times that of new buildings to 2 or 3 times the risk.
This meeting was followed at 6pm by the daily debriefing meeting.
Kelvin displayed many interesting maps and plots and the aerial photographs. Apparently the reduced LIDAR data will be available tomorrow.
Still no definitive depths to the sand horizons in the high liquefaction zones although this is shaping up to be a serious issue. People seem to be fairly resilient after the earthquake and continuing sequence of aftershocks. One farmer is battling to stop his land becoming a lake where it has subsided 1.5m.
Again we all went off to a local restaurant for a quick bite and then back to the motel to prepare for the following day, my last.

The earthquake is officially to be called the Darfield Earthquake and the fault The Greendale Fault