Quantitative Risk Analysis (QRA)

Timpanogos Cave National Monument

• The QRA is a module within the USMP.

• It is another decision-support tool.

• QRA can be used to further prioritize slopes, as part of abenefit-cost analysis, or as a stand alone module.

• The QRA uses numerical estimates of severity, probability,and exposure to place estimated risk into a societal context.

What is hazard?

What is risk?

1947

2010

Zion National Park

Consequence =

Occurrence = two events in 63 years

Hazard: Something that poses a theoretical possibility of harmto life, health, property or environment.

Risk: Is a probability. Risk takes into account the probabilitythat a certain event will occur and what theconsequence is if the hazard is realized.

Holmes, R. R., Jr., Jones, L. M., Eidenshink, J. C., Godt, J. W., Kirby, S. H., Love, J. J., Neal, C. A., Plant, N. G., Plunkett, M. L.,Weaver, C. S., Wein, Anne, & Perry, S. C., 2012, U.S. Geological Survey natural hazards science strategy- Promoting the safety,security, and economic well-being of the Nation: U.S. Geological Survey Circular 1383-F, 79 p.

Zion National Park

Slope Hazard Quantitative Risk Estimate

Places estimated risk from a perceived hazard into asocietal context.

General Risk Equation:Annual Individual Fatality or Injury Risk

=probability of occurrence - P(occ)

×probability of being affected by the event - P(loc)

×probability of people being in the hazard zone - P(pres)

×probability of a fatal consequence or injury - P(vul)

This kind of problem is a form of a Fermi estimate

This risk estimate equation is far from unique.

- Australian Geomechanics Society- Used to evaluate rockfall risk following the 2010 and 2011

Chirstchurch, NZ earthquakes (Massey et al., 2012, 2014).

Main drawback: Some factors may need to be estimatedMain benefit: Risk related to rockfall or landslides can becompared with other societal risks, even back-of-the-envelopeestimates are useful.

5 number Powerball1 in 11.7 Million

Jackpot1 in 292.2 Million

Societal risks

No policy on whatrisk level is toohigh

Typicalnatural hazardrisks

Largelyacknowledgedand acceptedsocietal risks

Risks of deathfrom commoncauses of mortalitysuch as canceror heart disease.

Ann

uali

ndiv

idua

lRis

kEx

pres

sed

aspr

obab

ility

Loga

rithm

icsc

ale

-Eac

hho

rizon

tall

ine

repr

esen

tsa

ten

fold

diffe

renc

ein

risk

10-3

10-4

10-5

10-6

10-7

10-2

Worldw

idelan

dslide

fatali

ties - 20

16

Natural

hazar

d fatali

ties,

5 yrav

erage

- NOAA

U.S. acci

denta

l fall f

ataliti

es

U.S. moto

r vehic

lefat

alitie

s

All U.S. a

ccide

ntal fa

talitie

s

U.S. can

cerfat

alitie

s

1 in a Million

1 in 100,000

1 in 10,000

1 in a Thousand

Nonfat

alan

d fatal

motor

vehic

leacc

idents

inNPS un

its.

Comparison of annual individual risk

3.0×10-7

1.9×10-6

1.0×10-4 1.1×10-4

4.3×10-4

1.9×10-3

1.6×10-5

CHCU

GRCA

DINO

Typicalnatural hazardrisks

Largelyacknowledgedand acceptedsocietal risks

Risks of deathfrom commoncauses of mortalitysuch as canceror heart disease.

Ann

uali

ndiv

idua

lfat

ality

Ris

kEx

pres

sed

aspr

obab

ility

Loga

rithm

icsc

ale

-Eac

hho

rizon

tall

ine

repr

esen

tsa

ten

fold

diffe

renc

ein

risk

10-3

10-4

10-5

10-6

10-7

10-2

Southe

rnCali

fornia

earthq

uake

estim

ate

Natural

Hazard

fatali

ties,

10yr

avera

ge- NOAA

U.S. Hom

icide

U.S. acci

denta

l falls

U.S. moto

r vehic

leacc

idents

All U.S. a

ccide

ntal fa

talitie

s

U.S. can

cerfat

alitie

s

5.4×10-7

2.1×10-6

5.2×10-57.8×10-5 1.1×10-4

3.8×10-4

1.7×10-3

Residential area rockfallrisk estimate range3.3×10-4 to 9.5×10-4

GRCA rockfallrisk estimate range6.2×10-6 to 3.2×10-5

Highestrisk estimate

DINO1.4×10-6

Comparison of annual individual fatality riskCHCU

1 in a Million

1 in 100,000

1 in 10,000

1 in a Thousand

5 number Powerball1 in 11.7 Million

Jackpot1 in 292.2 Million

Overhang2.7 m

Trail1.6 m

0 5 10 151340

1345

1350

1355

1360

1365

1370

1375

1380

Met

ersA

bove

Sea

Lev

el

Meters

ApproximateRockfall Source

Overhang7.7 m

Scotts Bluff National Monument

Ann

uali

ndiv

idua

lacc

iden

tris

kEx

pres

sed

aspr

obab

ility

Loga

rithm

icsc

ale

-Eac

hho

rizon

tall

ine

repr

esen

tsa

ten

fold

diffe

renc

ein

risk

10-3

10-4

10-5

10-6

10-7

10-2

Chanc

e ofa car

crash

durin

g a NPS visit

Natural

Hazard

Injuri

es,

10yr

avera

ge- NOAA

Dec.20

15Sad

dleRoc

k

Trail h

azard

zone

Saddle

Rock Tria

l risk

from

allroc

kfall s

ource

s

Three 8 hr

shifts

working

in

theDec.

2015

hazar

d zone

1.6×10-5

1.2×10-57.8×10-6

8.4×10-6

1.8×10-3

1 in a Million

1 in 100,000

1 in 10,000

1 in a Thousand

Typic

alSad

dleRoc

k

Trail ro

ckfal

ls

Comparison of annual individual accident risk estimates

5.7×10-7

Slope Hazard Quantitative Risk Estimate Work Sheet

Stopping Sight Distance (SSD) added to the length of thehazard zone at speeds above 15 km/h or 9.3 mph.

SSD equation from the National Cooperative HighwayResearch Program Report 400 (1997)

https://earthquake.usgs.gov/hazards/interactive/

Seismic Hazard - Ground motions trigger rockfall and landslides.

Mackey, B. H., & Quigley, M. C., 2014. Strong proximal earthquakes revealed by cosmogenic 3He dating of prehistoric rockfalls, Christchurch, NewZealand. Geology, 42(11), 975-978.

Massey, C. I., McSaveney, M. J., Heron, D., & Lukovic, B., 2012. Canterbury Earthquakes 2010/11 Port Hills slope stability: Pilot study for assessing life-safety risk from rockfalls (boulder rolls), GNS Science Consultancy Report 2011/311.

Massey, C. I., McSaveney, M. J., Taig, T., Richards, L., Litchfield, N. J., Rhoades, D. A., McVerry, G. H., Lukovic, B., Heron, D. W., Ries, W., & VanDissen, R. J., 2014. Determining rockfall risk in Christchurch using rockfalls triggered by the 2010-2011 Canterbury earthquake sequence, NewZealand. Earthquake Spectra, 30, 155-181.

Use USGS hazard curve to find the probability of greater than 0.2g

Grant, A., Wartman, J., Massey, C. I., Olsen, M. J., O’Banion, M., & Motley, M., In Review. The impact of rockfalls on dwellings during the 2011Christchurch, New Zealand earthquakes. Landslides, submitted 2016.

10-20 Kilojoule rockfall probably fatal.1 ft rock (146 lb) dropped from 55 ft

Oso landslide, WA 43 people killed, 74% (0.74) chance of fatality

Typicalnatural hazardrisks

Largelyacknowledgedand acceptedsocietal risks

Risks of deathfrom commoncauses of mortalitysuch as canceror heart disease.

Ann

uali

ndiv

idua

lRis

kEx

pres

sed

aspr

obab

ility

Loga

rithm

icsc

ale

-Eac

hho

rizon

tall

ine

repr

esen

tsa

ten

fold

diffe

renc

ein

risk

10-3

10-4

10-5

10-6

10-7

10-2

Worldw

idelan

dslide

fatali

ties - 20

16

Natural

hazar

d fatali

ties,

5 yrav

erage

- NOAA

U.S. acci

denta

l fall f

ataliti

es

U.S. moto

r vehic

lefat

alitie

s

All U.S. a

ccide

ntal fa

talitie

s

U.S. can

cerfat

alitie

s

1 in a Million

1 in 100,000

1 in 10,000

1 in a Thousand

Nonfat

alan

d fatal

motor

vehic

leacc

idents

inNPS un

its.

Comparison of annual individual risk

3.0×10-7

1.9×10-6

1.0×10-4 1.1×10-4

4.3×10-4

1.9×10-3

1.6×10-5

The worldwide landslide fatality data iscompiled by Dave Petley, University of Shetfield,after Petley, 2012. The 5 year average naturalhazard fatality risk is compiled from 2011-2015NOAA data. The chance of a car crash during aNPS visit is a 15 year average using NPS databetween 1990 and 2005. Other societal risksrepresented by blue bars are from data collectedby the CDC for the 2014 calendar year.

The benefit of preventing a fatality can be measuredby:

“Value of a Statistical Life”(VSL)

VSL in 2017 dollars ~ $9.6 million(US DOT VSL Gudance 2013)

This is a valuation in the reduction in risk.

Risk Reduction Cost/Benefit Analysis

Example

Point Reyes National SeashoreFatal bluff collapse on March 21st, 2015

Arch Rock

AIRD about1 in 3,0003.4×10-4

Higher than vehicle accidents

After dilation cracksappeared - high probabilityof failure within a month.30 m hazard zone.30 minutes on the point.50% chance of mortality.

Monthly valuation of reducingthe risk is estimated at about:

$557,000If 2,000 people spend 30 minat the point a month.

Typicalnatural hazardrisks

Largelyacknowledgedand acceptedsocietal risks

Risks of deathfrom commoncauses of mortalitysuch as canceror heart disease.

Ann

uali

ndiv

idua

lfat

ality

Ris

kEx

pres

sed

aspr

obab

ility

Loga

rithm

icsc

ale

-Eac

hho

rizon

tall

ine

repr

esen

tsa

ten

fold

diffe

renc

ein

risk

10-3

10-4

10-5

10-6

10-7

10-2

Southe

rnCali

fornia

earthq

uake

estim

ate

Natural

Hazard

fatali

ties,

10yr

avera

ge- NOAA

U.S. Hom

icide

U.S. acci

denta

l falls

U.S. moto

r vehic

leacc

idents

All U.S. a

ccide

ntal fa

talitie

s

U.S. can

cerfat

alitie

s

5.4×10-7

2.1×10-6

5.2×10-57.8×10-5 1.1×10-4

3.8×10-4

1.7×10-3

1 in 101 in 5

Arch RockRemainingHazard

Comparison of annual individual fatality risk

1 in 20

1 in a Million

1 in 100,000

1 in 10,000

1 in a Thousand

1 in 6 - 1 in 18ClosureMonitoring

Questions?