new 2142-13 advanced conference on seismic risk mitigation and...
TRANSCRIPT
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2142-13
Advanced Conference on Seismic Risk Mitigation and Sustainable Development
Zhenming Wang
10 - 14 May 2010
Kentucky Geological Survey University of Kentucky
Lexington USA
Seismic Hazard and Risk Assessment and Mitigation Policy in USA
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Seismic Hazard and Risk Assessment and Mitigation Policy in USA
Zhenming Wang, PhD, PE
Kentucky Geological SurveyUniversity of Kentucky
Lexington, KY 40506, [email protected]
www.uky.edu/KGS/geologichazards/
ICTP Advanced Conference on Seismic Risk Mitigation and Sustainable Development
10 - 14 May 2010
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Outline• Introduction
– The NEHRP Provisions – NRC Regulatory Guide 1.208
• Probabilistic Seismic Hazard Analysis (PSHA)
• Alternative Seismic Hazard Assessments – Seismic Hazard Analysis (SHA) – Deterministic Seismic Hazard Analysis (DSHA) – Neo-DSHA or Scenario-Based Hazard Analysis
• Lesson from Wenchuan, China, earthquake
• Summary
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Development of Design Ground Motion (Policy)
Seismic Hazard Map(USGS)
Seismic Design Ground Motions(FEMA)
BSSC – engineers,seismologists, and others
State Agencies Other organizationsFederal agencies
Policy
Science
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2009 NEHRP Provisions (Policy)
Figure 22-1 Uniform-hazard (2% in 50-Year) ground motions of 0.2-second spectral response Acceleration (5% of critical damping), Site Class B
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California
The central US
Paducah
San Francisco
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0.2-second spectral response Acceleration (5% of critical damping), Site Class B
1980 Sharpsburg Earthquake (M5.2)
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Development of Seismic Ground Motion (policy)
Seismic Hazard Map(USGS)
Seismic Design Ground Motions(FEMA)
BSSC – engineers,seismologists, and others
Impacts on society
Science - Basis
Stakeholders: Scientists/Engineers/Economist, …
Policy
PSHA
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Seven-Day Earthquakes
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(Leith and others, 2009)
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GPS results
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NMSZ
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Deformation rate: > 30 mm/y
Deformation rate: < 3 mm/y
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(Frankel and others, 1996)
NRC RG: 10-4 – 10-5
(annual frequency of exceedance)
10%
in 5
0 Ye
ars
5% in
50
Year
s
2% in
50
Year
s
HAZARD CURVES FOR SELECTED CITIES
0.10000 0.01000 0.00100 0.00010 0.00001
Annual Frequency of Exceedance
0.0
0.1
1.0
10.0
0.2
sec
Spec
tral
Acc
eler
atio
n, %
g
CITIESLos AngelesSan FranciscoSeattleSalt Lake CityNew York CityCharlestonMemphis
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Yucca Mountain, NV(Stepp and others, 2001)
Example:100,000,000y RP,11g PGA?
It was concluded in 2008 that “while many of the observations we present here are preliminary, they nevertheless suggest that the 1998 PSHA overstates the true seismic hazard at Yucca Mountain” (Abrahamson and Hanks, 2008)
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Development of mitigation policy in US
Seismic Design Ground Motions
Engineers, seismologists, and others
Impact on society
Science - Basis
Stakeholders: Scientists/Engineers/Economist, …
Policy
PSHA
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Seismic Hazard versus Seismic Risk
• Seismic Hazard– Quantification:
• Physical measurement (magnitude, PGA, MMI)
• Temporal measurement• Spatial measurement
• Seismic Risk– Quantification:
• Probability• Physical/monetary measurement• Temporal measurement• Spatial measurement
Seismic Risk= Seismic Hazard Θ Vulnerability
References1. Wang, Z., 2009, Seismic hazard vs. seismic risk, Seismological Research
Letters, 80: 673–674. 2. Panza and others (in press), Introduction, Pure and Applied Geophysics,
Special Volume on Advanced Seismic Hazard Assessment
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Seismic Hazard vs. Seismic Risk
ConsequenceVulnerability: car and people
Risk = Seismic Hazard Θ Vulnerability
Hazard may or may not be mitigated, but risk can always be reduced
Seismic hazard: rock falls (rockfalls/minute)
(the probability killed by a rockfall during passing through)
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Seismic Hazard vs. Seismic Risk
)/exp(1 RItp ���
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Probabilistic Seismic Hazard Analysis – PSHA
Developed by Cornell in 1970 (Cornell, 1968, 1971)
(McGuire, 2004)
dmdrrfmfydyy
vyYvPy RMy
mr
y
y
)()()}(ln]2
)ln(lnexp[
211{)()( 2
ln,
2
ln,0 ����
������ ���
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PSHA end result: a hazard curve of ground motion vs. “frequency” at a site
10%
in 5
0 Ye
ars
5% in
50
Year
s
2% in
50
Year
s
HAZARD CURVES FOR SELECTED CITIES
0.10000 0.01000 0.00100 0.00010 0.00001
Annual Frequency of Exceedance
0.0
0.1
1.0
10.00.
2 se
c Sp
ectr
al A
ccel
erat
ion,
%g
CITIESLos AngelesSan FranciscoSeattleSalt Lake CityNew York CityCharlestonMemphis
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Infinite GMA single EQ OutputInput
PSHA
“Model”
Sensitivity Test
Probabilistic Seismic Hazard Analysis – PSHA
d
Site(GM occurrence)
TRP=?
Source(M7.7 occurrence)
TRI =500 years
TRP: 500y to infinity?(Cornell, personal communication, 2004)
Dis. =30km
The return period: “the mean (average) time between occurrences of a seismic hazard, for example, a certain ground motion at a site” (McGuire, 2004, p.8).
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Probabilistic Seismic Hazard Analysis – PSHA
VSAP
New Madrid Seismic Zone
TRI =500 years
TRP=500 years
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Probabilistic Seismic Hazard Analysis – PSHA
What is PSHA?
γ(y): the annual probability of ground motion y being exceeded
It was developed from mathematical statistics (Benjamin and Cornell, 1970; Mendenhall and others, 1986) under four fundamental assumptions (Cornell 1968, 1971):
(a) Constant-in-time average occurrence rate of earthquakes(b) Equal likelihood of earthquake occurrence along a line or over an areal source (single point) (c) Variability of ground motion at a site is independent(d) Poisson (or "memory-less") behavior of earthquake occurrences.
dmdrrfmfydyy
vyYvPy RMy
mr
y
y
)()()}(ln]2
)ln(lnexp[
211{)()( 2
ln,
2
ln,0 ����
������ ���
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Probabilistic Seismic Hazard Analysis – PSHA
GMPE: �� ���� ),(),()ln( RMfRMfY
1. δ distribution depends on σ, but not on ε2. ε is a standardized normal distribution with a zero mean and standard deviation of 1
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Probabilistic Seismic Hazard Analysis – PSHA
GMPE:
According to mathematical statistics (Benjamin and Cornell, 1970; Mendenhall and others, 1986), if and only if M, R, and δare independent random variables, then the exceedance probability P[Y�y] for seismic source j is
�� ���� ),(),()ln( RMfRMfY
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Probabilistic Seismic Hazard Analysis – PSHA
Assumption (a): Constant-in-time average occurrence rate of earthquakes. For G-R relationship
PDF for M
M is independent
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Probabilistic Seismic Hazard Analysis – PSHA
Assumption (b): Equal likelihood of earthquake occurrence along a line or over an areal source (single point)
PDF for R
R is independent
(Cornell, 1968)
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Probabilistic Seismic Hazard Analysis – PSHA
]2
)ln(exp[21)( 2
2
��
��� mryf �
��
�� ���� )ln(),()ln( MRYRMfY
]12
)ln(exp[12
1)( 2
2
��
�� mryf �
PDF for ε
PDF for δ
Assumption (c): Variability of ground motion at a site is independent
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Probabilistic Seismic Hazard Analysis – PSHAAssumption (d) Poisson (or "memory-less") behavior of earthquake occurrences
dmdrrfmfydyyyYP jRjMj
mr
j
y
j )()()}(ln]2
)ln(lnexp[2
11{][ ,,2
2
0 ����
���� ���
(page 1590 of Cornell, 1968)
�� ���� ),(),()ln( RMfRMfY
0mj
jjev �� ��
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Probabilistic Seismic Hazard Analysis – PSHA
(page 1590-91 of Cornell, 1968)
Pre-condition (2) Small annual prob. of exc. ≤ 0.05
Pre-condition (1), t ≡ 1 (year)
...!
...!2
12
������nxxxe
nx
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Probabilistic Seismic Hazard Analysis – PSHA
The return period
The annual probability of exceedance – probability of exceedance in ONE year
Pre-condition (1): t ≡ 1 (year) Pre-condition (2): ≤ 0.05
dmdrrfmfydyyvy RMy
mr
y
y
)()()}(ln]2
)ln(lnexp[2
11{)( 2ln,
2
ln,0 ���� �
��� ���
Basic Equation of PSHA (total annual probability of exceedance)
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Probabilistic Seismic Hazard Analysis – PSHA
2) Pre-condition (2) small annual prob. of exc. ≤ 0.05
1) Pre-condition (1) t ≡ 1 (year)
Assumption (d): Poisson (or "memory-less") model
1. If any of the assumptions is not valid, PSHA calculation is NOT valid.2. If any of the pre-conditions is violated, PSHA calculation is NOT valid.3. The annual probability of exceedance is a PROBABILITY of exceedance in ONE year and dimensionless.
dmdrrfmfydyyvy RMy
mr
y
y
)()()}(ln]2
)ln(lnexp[2
11{)( 2ln,
2
ln,0 ���� �
��� ���
Assumption (c): Variability of ground motion at a site is independent
Assumption (b): Single point source
Assumption (a): Constant-in-time average occurrence rate of earthquakes
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Probabilistic Seismic Hazard Analysis – PSHA
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Source model: finite fault, not point source
Haiti earthquake
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Probabilistic Seismic Hazard Analysis – PSHA
δ (σ) is not independent
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Probabilistic Seismic Hazard Analysis – PSHA
2) Pre-condition (2) small annual prob. of exc. ≤ 0.05
1) Pre-condition (1) t ≡ 1 (year)
Assumption (d): Poisson (or "memory-less") model - ?
1. PSHA (model) is NOT valid.2. The annual probability of exceedance is a PROBABILITY of exceedance in ONE year and dimensionless - Not “frequency”.
dmdrrfmfydyyvy RMy
mr
y
y
)()()}(ln]2
)ln(lnexp[2
11{)( 2ln,
2
ln,0 ���� �
��� ���
Assumption (c): Variability of ground motion at a site is independent - No
Assumption (b): Single point source – Not valid
Assumption (a): Constant-in-time average occurrence rate of earthquakes ?
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Yucca Mountain, NV(Stepp and others, 2001)
Probabilistic Seismic Hazard Analysis – PSHA
PSHA could “create”11g PG with a returnperiod of 100,000,000 years.
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Probabilistic Seismic Hazard Analysis – PSHA
Pre-condition (1): t ≡ 1 (time unit) Pre-condition (2): ≤ 0.05
Assumption (d) Poisson (or "memory-less") behavior of earthquake occurrences
Example: tossing a coin
ph=0.5
pt=0.5
The probability of having at least one head in 1 minute5.0
v = 10 (tosses/min.)
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Spatial
Temporal
Alternative Seismic Hazard Assessment
(Reiter, 1990)
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Spatial
Temporal
1. Seismic Hazard Assessment - Theoretical
��� ),()ln( RMfY
),ln,( �YRgM �
bMaeN
303.2303.21 �����
),ln,(303.2303.21 �� YRbgaeN
����
PGA
Exceedance frequency
(Wang, 2006, 2007)
Median+SD (84%)
Median-SD (16%)
median
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0.0001
0.0010
0.0100
0.1000
1.0000
4.0 5.0 6.0 7.0 8.0
Magnitude (M)
Log
(N)
SHA to DSHA
Ground motion at 30km:0.44g PGA (median) 0.22g PGA (median–SD) 0.88g PGA (median+SD) /RP≡500y
Characteristic earthquake:M7.5/RI=500y
For one characteristicEarthquake:SHA becomes DSHA
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Maximum Credible Earthquake
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PGA for Maximum Credible Earthquake
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SHA to DSHA to Neo-DSHA
Neo-DSHA (Panza and others, 2001)
(Macpherson and others, 2009)
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SHA to DSHA to Neo-DSHA
Limitation:<0.5 Hz
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SHA to DSHA to Neo-DSHA
Reelfoot (central) fault rupture
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Year A (PGA,g) Rank (m) P
1895 0.001 96 0.888889
1896 0.01 84 0.777778
1897 0.1 29 0.268519
Step 2
(Milne and Davenport, 1969)
Step 3
(ground motion at a site)
Seismic hazard curve: A vs. τ at a site
2. Seismic Hazard Assessment - Empirical
(Historical records)
Step 1
Intensity table (Panza)
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1��
NmP
Step 3
Step 4
(ground motion at a site)
(N is total number ofyears of records)
mN
P11 �
���Seismic hazard curves
Year A (PGA,g) Rank (m) P
1895 0.001 96 0.888889
1896 0.01 84 0.777778
1897 0.1 29 0.268519
2. Seismic Hazard Assessment - Empirical
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(Bozkurt and others, 2007)
Tokyo, Japan(400-year data)
2. Seismic Hazard Assessment - Empirical
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Beijing area, China (500 years data)(Xie and others, in press)
Tainjin CityBeijing City
2. Seismic Hazard Assessment - Empirical
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Lesson from Wenchuan Earthquake
Magnitude: 8.0 (7.9 USGS) Fault Rupture: ~300 km x 30 kmSurface Displacement: 5m (v), 4.8m (h) Largest Recorded PGA: 0.65gDeath: ~70,000Missing: ~20,000Injured: ~380,000Economic loss: >US$120B
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Lesson from Wenchuan Earthquake
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(Li and others, 2008)
Lesson from Wenchuan Earthquake
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Wolong
Qingping
Zengjia
Rupture and asperity effects
Lesson from Wenchuan Earthquake
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0.10g
0.15g
0.20g
0.05g
0.12g
0.14g
0.16g
0.18g
0.20g0.65g
Design PGA(10% PE in 50 yrs
0.10g
0.30g
Lesson from Wenchuan Earthquake
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Summary• Probabilistic seismic hazard analysis:
PSHA (model) is flaw• Is not based on earthquake science
• Invalid physical models• point source• Poisson distribution
• Invalid mathematics• Mis-interpretation of annual probability of
exceedance or return period• Become a pure numerical “creation”
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Summary• Alternative seismic hazard assessment
• The goal of any seismic hazard assessment is to quantify
• Physical measurement (ground motion)• Temporal measurement (when/how often)• Spatial measurement (where)
• Approaches• Theoretical
• SHA• DSHA• Neo-DSHA
• Empirical
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Summary• Seismic hazard and risk are different
concepts, and play different roles in policy making
• Earth-scientists, seismologists in particular, must • provide seismic hazard information that is
consistent with modern sciences• also communicate the information in an
understandable way • work with engineers and others to assess seismic
risk
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Thank you very much!