GNS Science Natural Hazards Research Platform Progress in understanding the Canterbury Earthquakes...

GNS ScienceNatural Hazards Research Platform

Progress in understanding the Canterbury Earthquakes

Kelvin BerrymanManager, Natural Hazards Research Platform

Dr. Matt Gerstenberger – GNS ScienceDr Philip Barnes – NIWA

Prof Jarg Pettinga – University of Canterbury

GNS Science

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Aftershock Decay Rate

Natural Hazards Research Platform

GNS Science

Long-term (50yr) Earthquake Rate Forecast

• Used to inform update of building codes

• Accounts for different earthquake clustering scales

• Combines four different models• Used to estimate probabilities of

ground shaking

• Short-term clustering model• Days to Year(s)

• Medium-term clustering model• Years to decades

• Long-term average model• Average earthquake rate since

1960• NSHM fault model

• Longest-term mostly time-independent Yearly number of earthquakes greater than

magnitude 5 from three models



Magnitude 5.0-5.9 Magnitude 6.0-6.9

Start date & Length

1 week 30 days 1 year 1 week 30 days 1 year

May 19th 2011

1 in 8 1 in 3 9 in 10 1 in 100 1 in 20 1 in 4

May 19th 2012

1 in 30 1 in 10 7 in 10 <1 in 100 1 in 100 1 in 10

Extended probabilities of aftershocks and larger events for Canterbury following the 2010 Darfield earthquake from short-term model

All earthquakes up to May 16th 2011 were used for these calculations. These forecasts are anticipated to change as the sequence continues to develop. •The occurrence of a larger aftershock will temporarily increase the probabilities•Extended “quiet times” may cause a decrease in the probabilities•Each day a larger event does not occur, the probabilities decrease•Probability of a M6.0 is approximately 10 times that of a 6.9


So, if there are going to be further large aftershocks or triggered events, where might they occur…….

– this is why we have turned to geophysical surveys to investigate where bedrock faults occur with any evidence of recent movement

GNS Science

Canterbury has many active faults that contribute to the

earthquake hazard

Faulting ..….. and the Earthquake-driven LandscapeFaulting ..….. and the Earthquake-driven Landscape

Key Questions:


Pettinga et al. (1998)

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Greendale Fault

Geology map source: GNS Science QMap series & University of Canterbury


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Onshore seismic reflection linesOnshore seismic reflection linesand aftershock mapand aftershock map

11

22

33

44

55

66


GNS Science

De

pth

(m

)

0

500

1000

Lyttelton Volcano Paleo-topography

8 km

South North

Port Hills fault


Line 1 - New Brighton Beach

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Line 2 - Barbadoes Street

Lyttelton railway line Barbadoes Street

Lyttelton VolcanoPaleo-topographyD

ep

th (

m)

0

500

1000

channel

South North

3.7 km


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Investigating Canterbury subsurface structure

Near surface variations in rock density

• Red lines are known surface active faults• Dots are gravity measurement locations


Magnetic signature of rocks

GNS Science

• Collection finished last week. • Variations are dominantly due to volcanism (12-6 Ma Banks Peninsula)• Buidings and other man-made features need to be identified


Variations in magnetic signature of bedrock


Variations in bedrock

topography

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Multichannel Seismic Reflection data


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Is there active faulting south of the Pegasus Bay Fault?

YES, but the faults must have very low vertical slip rates


GNS Science

1. Faults imaged appear to have extremely low movement rates consistent with very long intervals between major earthquakes

2. There is no evidence of aftershocks stepping onto further offshore faults

3. Further results relating to the seismic profiling southwest and west of the city will become available in a month or so

4. Evidence for low rates of fault movement across the region derived from the subsurface geophysical studies is consistent with assessment that the September and February earthquakes are rare occurrences in Canterbury

5. Forecasts for earthquake activity in the future (1-50 years) has been incorporated into a revision of the building code for the rebuild programme in Canterbury 6. The research teams will be focusing on the integration of the various datasets to provide more confident assessment of earthquake likelihood

In Summary


GNS Science Natural Hazards Research Platform Progress in understanding the Canterbury Earthquakes...

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