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8/8/2019 War Wick Smith

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Earthquake risk assessment:Earthquake risk assessment:from scientific research to riskfrom scientific research to risk

management decisionsmanagement decisions

Warwick SmithWarwick Smith

GNS Science, Lower HuttGNS Science, Lower Hutt


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Last 50 yearsPrevious 100 years


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NZsNZs largest historical earthquake:largest historical earthquake:

1855 Wairarapa1855 WairarapaMagnitudeMagnitude

Recurrence intervalRecurrence interval

UpliftUplift

Severity of ground motionSeverity of ground motionDamage and casualtiesDamage and casualties

None of these is a measure of theNone of these is a measure of thehazard or risk in Wellingtonhazard or risk in Wellington


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To estimate theTo estimate the hazardhazard in a particular placein a particular placewe must ask:we must ask:

1.1. Which earthquake sources affect this location?Which earthquake sources affect this location?

2.2. How often do earthquakes occur at each source,How often do earthquakes occur at each source,

and how big will they be?and how big will they be?

3.3. How severe will the ground motion be?How severe will the ground motion be?

To estimate theTo estimate the riskrisk, we must also ask:, we must also ask:4.4. What will be the effects on particular assets?What will be the effects on particular assets?


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WellingtonWellington

Strong Shaking

MMIX

Extensive Damage


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The Wellington FaultThe Wellington Fault

Magnitude 7.5Magnitude 7.5Recurrence Interval 600 yearsRecurrence Interval 600 years

(on average, not on schedule)(on average, not on schedule)Last one ~ 400 years agoLast one ~ 400 years ago

Next one?Next one? Next weekNext weekEventuallyEventually


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In addition to the catalogue ofIn addition to the catalogue offaults, afaults, a BackgroundBackground

Seismicity ModelSeismicity Model takestakes

account of the distributedaccount of the distributedearthquake activityearthquake activity

throughout the country.throughout the country.


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Modified Mercalli intensity scaleModified Mercalli intensity scale


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Modified Mercalli intensity scaleModified Mercalli intensity scale


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Intensity Decreases as you go Further Away

4

6

8

10

12

1 10 100 1000

Distance, km

MMI

nte

nsity

Dowrick-Rhoades Intensity Function

Mag 87

65

Distance (km)


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Hazard in terms of spectral accelerationHazard in terms of spectral acceleration

rather than intensityrather than intensity

Peak ground accelerationPeak ground acceleration

Ground motion at various periodsGround motion at various periods

Site conditionsSite conditions

Building codesBuilding codes


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Damage RatioDamage Ratio

Cost of RepairCost of Repair

Replacement Value of the AssetReplacement Value of the Asset

Its a number between 0 and 1Its a number between 0 and 1

Repair Cost = Value X DRRepair Cost = Value X DR

If we know theIf we know the intensityintensity and theand thebuilding typebuilding type we can estimatewe can estimate

what thewhat the damage ratiodamage ratio is likely to beis likely to be


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01

2

3

4

5

6

7

8

9

0 10000 20000 30000 40000 50000

Year

EQCL

oss(b)

NZ houses cost of damageWellington area faults Other sources

Lo

ss

(b$)


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EQC Housing Portfolio

0

1

2

3

4

5

0 200 400 600 800 1000

Return Period (years)

Lo

ss($b)

EQC Housing Portfolio

Return period (years)

Deductible?

Layers?

Typical loss curve for an asset portfolio

Loss($m)


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Site B

0

5

10

15

20

25

30

35

40

45

50

0 500 1000 1500 2000 2500 3000

Return Period (years)

Loss($m)

Loss Curve - Fragile Industrial Plant


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Important Earthquake Sources

Wellington Portfolio

Wellington

Wairarapa

Ohariu

ShepherdsGully

SubductionZone


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Wellington Fault Severity Distribution

0

100

200

300

400

500

600

700

800

900

1000

1000 3000 5000 7000

EQC Loss ($m)

Fre

quency

Frequency

50% 4.2 75% 4.9

90% 5.5

1 2 3 4 5 6 7 8

Loss ($m)

Fre

quency


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Good decisions in risk management requireGood decisions in risk management require

reliable assessment of hazard and riskreliable assessment of hazard and risk

InsuranceInsurance

Mitigation worksMitigation works

Priority settingPriority setting

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