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