Earthquake Impacts in the Christchurch CBD Impact… · Lateral spreading and its impacts in urban...
Transcript of Earthquake Impacts in the Christchurch CBD Impact… · Lateral spreading and its impacts in urban...
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Earthquake Impacts
in the Christchurch CBD
Prof Jarg Pettinga & Dr Tom Wilson
Dept. Of Geological Sciences
Thanks to Dr Matthew Hughes (UC), Professor Misko Cubrinovski (UC), Ian McCahon (Geotech Consultants) for additional material
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Overview of the Presentation
Jarg:
• The seismic context & liquefaction
Tom:
• Potable Water Supply
• Waste Water Network
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Magnitude/Time plot of the earthquake sequence to date
incomplete detection
often not felt
generally felt
Total now well over 11,000 recorded events
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Graph depicts the significant effect of the February, June and December 2011 earthquakes re-
energising the Darfield aftershock sequence (Source: GNS Science).
(X1
0)
June 13/11
M6.3
Feb 22/11
M6.3
Dec 23/11
M6.0
Sept 4/10
M7.1
Aftershock Decay Sequence for Canterbury - Magnitude 3 and greater
Source: www.geonet.org.nz
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Liquefaction
“Transformation of a saturated granular material from a solid to a liquefied state”
Earthquakes
• Magnitude
• Duration
Alluvial sediments
• Silts, sands, gravels
“Granular material”
Groundwater
• Water table depth
“Saturated”
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Liquefaction
Obermeier et al. (2005). Field occurrences of liquefaction-induced features: a primer for engineering geologic analysis of paleoseismic shaking. Engineering Geology 76, 209–234.
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Liquefaction
Courtesy Misko Cubrinovski
Settlement
Initial
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Liquefaction
Obermeier et al. (2005). Field occurrences of liquefaction-induced features: a primer for engineering geologic analysis of paleoseismic shaking. Engineering Geology 76, 209–234.
Crust
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Liquefaction
Obermeier et al. (2005). Field occurrences of liquefaction-induced features: a primer for engineering geologic analysis of paleoseismic shaking. Engineering Geology 76, 209–234.
Source sand
Crust
Potable Water & Waste Water Pipes
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Liquefaction – Christchurch East, June 2011
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Liquefaction – Christchurch East, June 2011
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Liquefaction – Christchurch East, June 2011
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Liquefaction – Christchurch East, June 2011 (Courtesy Merrick Taylor)
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Lateral spreading – liquefaction-induced slumping of banks into rivers
Avon River
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Lateral spreading – liquefaction-induced slumping of banks into rivers
Cubrinovski et al. (2012). Lateral spreading and its impacts in urban areas in the 2010-2011 Christchurch
earthquakes. New Zealand Journal of Geology and Geophysics.
South Brighton Bridge
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SEP 2010
JUN 2011
FEB 2011
Mapped Liquefaction - University of Canterbury
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Water Table – Factor of Safety Against Liquefaction beyond areas of mapped liquefaction
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Cubrinovski et al. (2011). Liquefaction Impacts on Pipe Networks. Short Term Recovery Project No. 6, Natural Hazards Platform, December
2011, University of Canterbury
Water Supply Damage
post-22 February 2011
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Cubrinovski et al. (2011). Liquefaction Impacts on Pipe Networks. Short Term Recovery Project No. 6, Natural Hazards Platform, December
2011, University of Canterbury
Water Supply Damage
post-22 February 2011
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Waste Water
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Growth of a city:
Subterranean expansion
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Edgeware Road - Wastewater Northern Relief Trunk Main
• Large and fast flow (~1 cumec), large amount of sediment transported through broken pipe.
• This section of the Northern Relief caused ~3 months delay during construction due to poor
ground conditions and groundwater issues.
Waste Water Pipe Collapse and Ground Failure
Photos and comments courtesy of Ben Pritchard, SCIRT
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Edgeware Road - Wastewater Northern Relief Trunk Main
• Large and fast flow (~1 cumec), large amount of sediment transported through broken pipe.
• This section of the Northern Relief caused ~3 months delay during construction due to poor
ground conditions and groundwater issues.
Waste Water Pipe Collapse and Ground Failure
Photos and comments courtesy of Ben Pritchard, SCIRT
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Vienna St, Waltham, shortly after 22 February 2011
• Service to the large upstream catchment (most of Beckenham) was still able to be provided by
pumping the downstream manhole – natural conduit formed due to high flows?
Waste Water Pipe Collapse and Ground Failure
Photos and comments courtesy of Ben Pritchard, SCIRT
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Alexandra St, Lower Richmond during winter snowfall, 2011
Rain and snow events caused new holes/cavities to open up overnight.
Waste Water Pipe Collapse and Ground Failure
Photos and comments courtesy of Ben Pritchard, SCIRT
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Alexandra St, Lower Richmond during winter snowfall, 2011
Rain and snow events caused new holes/cavities to open up overnight.
Waste Water Pipe Collapse and Ground Failure
Photos and comments courtesy of Ben Pritchard, SCIRT
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2: Consequences – the numbers • A large (for NZ) natural hazard event in a small economy
• 10% of NZ’s 4.5 million people directly impacted
• Total loss estimates c. $30B NZD – about 10-12% GDP
• 10,000’s homes damaged and >1,100 buildings demolished
• Reduced habitability and strained city’s ability to accommodate it’s residents
• 7,500 residential properties retired: ~5% of total housing stock
• Central Business District closed for months: 800 buildings demolished over 40 Ha (85%)
• New Zealand’s largest short-term migration
• 70,000 people evacuated: 19% of population
• 7,000-9,000 net long term migration: <3% of population
• 8 millions tonnes of disaster waste: 40 years of Chch waste
• One of the greatest geotechnical disasters of the modern age
• Liquefaction ground damage - flats
• Slope stability – (Port) Hills
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The CBD problem
• 6000 businesses and over 51,000 workers.
• Social and economic hub
• The closure of the CBD caused 100% stoppage
of economic activity within the cordon.
• Building types, neighbourhood effect,
organisational vulnerabilities
• Approximately 1300 buildings (over 60% of
commercial buildings in Chch CBD) have been
marked for demolition
• Not because a significant danger, but deemed
uneconomic to repair
• Major relocation to hubs/clusters
• Access to services, Confidence in buildings
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Regional economy continued to be strong (based on agriculture)
• Port, airport, road and rail networks had very little downtime
• 95% of businesses are still operating albeit with downturn in tourism,
education, and hospitality
• Some migration away from Canterbury especially immediately after event
• Net migration about 9,000 persons,
• 30,000 new workers needed for rebuild
• Communities remained largely intact
• There was no need for widespread evacuation from Christchurch
• Early government support for local business continuity and workforce
All DOOM and GLOOM...??? Well, not really...
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Event Date Country Economic Economic losses Insured Insurance Losses as %GDP Losses Industry US$B Contribution 11 March 11 Japan up to 300 up to 5.4% 35 up to 17% 27 Feb 10 Chile 30 18.6% 8 27% 22 Feb 11 NZ 15 10% 12 80% 12 Jan 10 Haiti 8 121% 0.1 1% 04 Sept 10 NZ 6 5.3% 5 81% 06 April 09 Italy 4 0.2% 0.5 14% 23 Oct 11 Turkey 0.75 0.1% 0.03 4% 04 April 10 Mexico 0.95 0.09% 0.2 21% Source: Swiss Re sigma catastrophe database
Insurance Perspectives - Recent Major Earthquake Events USD billion (at 2011 prices)
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Lessons from the Canterbury Earthquake Sequence
• Success and limitations of geoscience...
• What can we unpack from this?
• Very difficult situation
• Sustained earthquake sequence in a previously seismically ‘quiet’ region
• Unmapped faults
• Sequence has migrated across an major urban area
• Most damaging EQ since the 1931 Napier earthquake