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February 12, 2014
Adrian Rodriguez-Marek, Ph.D.
Associate Professor
The Charles E. Via, Jr. Department of Civil and
Environmental Engineering
TWENTY YEARS AFTER NORTHRIDGE:ENGINEERING LESSONS
Cat Modeling 2014, Orlando , Florida
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Outline
Northridge EQ: event summary
Engineering lessons learned
Structural
GeotechnicalGround motions
Progress in hazard assessment in the last 20 years
Future trends
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A little about myself
Civil Engineer (B.S., M.S., and Ph.D.)
Career as a Geotechnical Earthquake Engineer
Ph.D. topic: Near-Fault Ground Motions (U.C. Berkeley,2000)
Research: Site response, liquefaction, ground motionprediction, seismic hazard analysis
Consulting
Seismic hazard assessment of nuclear power plants Thyspunt Siting Project, South Africa
Pacific Northwest National Lab and CGS, Hanford, WA
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Northridge Earthquake: General Data
Date: 17 January, 1994
Time: 4:30:55 AM (local time)
Magnitude: 6.7 (Moment Magnitude)
Focal Depth: 19 km
Blind-thrust event
Event Summary Engineering Lesson s Learned Progress in Hazard Ass essment Future Trends
From. http://earthquake.usgs.gov/earthquakes/states/events/1994_01_17.php
From P. Somerville
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Northridge Earthquake: Damage
60+fatalities
9,000 injured
20,000 homeless, 40,000 buildings damaged
1,600 red-tagged 7,300 yellow tagged
20 - 25 Billion dollars in estimated losses (source:
USGS)
Event Summary Engineering Lesson s Learned Progress in Hazard Ass essment Future Trends
From. http://pubs.usgs.gov/of/1996/ofr-96-0263/introduc.htm)
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Northridge Earthquake: Damage
Ground motion intensity
was high in the near fault,
but not beyond
design ground motions formost structures
Significantly more damage
than would be expected
for a M 6.7 event
Event Summary Engineering Lesson s Learned Progress in Hazard Ass essment Future Trends
From. http://pubs.usgs.gov/of/1996/ofr-96-0263/introduc.htm)
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Engineering Lessons Learned
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Structural Engineering
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From Silva (1991)
Engineering
Seismology/Ground
Motion Engineering
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From Silva (1991)
Geotechnical Engineering
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Engineering Lessons Learned: Structural Engineering
Northridge was a Structuralearthquake Major lessons Steel structures Unexpected fractures in moment connections
Fractured steel braces in braced frames
Concrete structures Large deformations in floor diaphragms
Brittle columns
Known vulnerabilities that were exposed
Soft Storycollapse, masonry structures Non-structural components Significant damage led to large losses
Event Summ ary Engineering Lesson s Learned : Structural Hazard Ass essment Future Trends
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Engineering Lessons Learned: Steel Structures
Unexpected fractures in steel moment frame beam-tocolumn connections
Primary problem: brittle fractures of the weld between
beam flange and column flange
Event Summ ary Engineering Lesson s Learned : Structural Hazard Ass essment Future Trends
Sketch courtesy of T.Sabol, EnglekirkInstitutional, Inc
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Engineering Lessons Learned: Steel Structures
Unexpected fractures in steel moment frame beam-tocolumn connections
Event Summ ary Engineering Lesson s Learned : Structural Hazard Ass essment Future Trends
From PropertyRisk.com
From Forell.com andMichael Engelhardt
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Engineering Lessons Learned: Steel Structures
Unexpected fractures in steel moment frame beam-tocolumn connections: Causes
NOT: excessive ground motions
Many fractures occurred in buildings that should have
responded elastically (Mahin, 2014)
Most buildings were stronger than minimum code forces
Design issues: connections not properly tested, deep steel
beams
Construction issues: poor welding quality
Inspection problems
Event Summ ary Engineering Lesson s Learned : Structural Hazard Ass essment Future Trends
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Engineering Lessons Learned: Steel Structures
Major research initiatives: FEMA/SAC Steel Project
Event Summ ary Engineering Lesson s Learned : Structural Hazard Ass essment Future Trends
From S. Mahin,Northridge at 20Symposium
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Engineering Lessons Learned: Steel Structures
20 years later: resulting changes FEMA/SAC research reports
FEMA-350: Design Criteria for New Buildings
FEMA-351: Existing Welded Steel Moment-Frame Buildings
FEMA-352: Recommended Post-earthquake Evaluation and Repair FEMA-353: Quality Assurance Guidelines
FEMA-354: Policy Guide for Steel Frame Construction
Improve quality of welding materials
AISC Seismic provisions: expanded
AISC Connection prequalification standard
Event Summ ary Engineering Lesson s Learned : Structural Hazard Ass essment Future Trends
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Engineering Lessons Learned: Concrete Structures
Large deformations in long-span diaphragms Excessive diaphragm flexibility
Code level diaphragm forces were several times too
small
Event Summ ary Engineering Lesson s Learned : Structural Hazard Ass essment Future Trends
Northridge Fashion Center Parkinggarage (EERI Recon report)
CSUN parking structure in1994 (EERI Recon report)
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Engineering Lessons Learned: Concrete Structures
NEES project: Seismic Design Methodology for PrecastBuilding Diaphragms (U. Arizona, UCSD, U. Buffalo,Lehigh U.)
Fleischman, R. B.; Naito, C.; Restrepo, J.; Sause R.; and Ghosh, S. K., "Seismic DesignMethodology for Precast Concrete Diaphragms, Part 1: Design Framework," PCI
JOURNAL, 2005 Rodriguez, M.E., Restrepo, J. and Blandon, Seismic Design Forces for Rigid Floor
Diaphragms in Precast Concrete Building Structures, JSE, 2007.
Actual diaphragm forces far exceed ASCE 7-05specified diaphragm forces
BSSC Provisions Updated Committee on diaphragmforces
Event Summ ary Engineering Lesson s Learned : Structural Hazard Ass essment Future Trends
E i i L L d N St t l
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Engineering Lessons Learned: Non-Structural
Components
Olive View Hospital
Near elastic response
Ground accelerations were amplified (0.91g free field
and 2.31g at roof (Celebi 1997, JSE) Removed from use due to extensive nonstructural damage
(sprinklers, light fixtures, etc)
Event Summ ary Engineering Lesson s Learned : Structural Hazard Ass essment Future Trends
E i i L L d N St t l
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Engineering Lessons Learned: Non-Structural
Components
Recognition of large damages/cost due to non-structuralcomponents
NEES Project, UNR (http://www.nees-nonstructural.org/)
Response of the nonstructural components, as part of a
system under large drifts/accelerations.
Interactions within and between the nonstructural components.
Interactions between the components and the structure.
Effects of structural yielding on response of the nonstructural
components.
Event Summ ary Engineering Lesson s Learned : Structural Hazard Ass essment Future Trends
Engineering Lessons Learned Non Str ct ral
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Engineering Lessons Learned: Non-Structural
Components
Damages resulting from the Northridge EQ resulted ina push for PERFORMANCE BASED EARTHQUAKE
ENGINEERING
Event Summ ary Engineering Lesson s Learned : Structural Hazard Ass essment Future Trends
Performance Based Earthquake Engineering:
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Moehle (2003)
Performance Based Earthquake Engineering:PEER methodology
Ground Motion Intensity Measure(s)
Simple parameterizations of (complex) seismic ground motions Predictable as a function of site/seismic parameters
Full probability distribution function(s)
Relevant: can be related to structural response
Event Summ ary Engineering Lesson s Learned : Structural Hazard Ass essment Future Trends
Performance Based Earthquake Engineering:
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Moehle (2003)
Performance Based Earthquake Engineering:PEER methodology
Engineering Demand Parameter(s)
Quantify structural response Predictable as a function of IMs
Full probability distribution function(s)
Relevant: can be related to structural damage
Event Summ ary Engineering Lesson s Learned : Structural Hazard Ass essment Future Trends
Performance Based Earthquake Engineering:
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Moehle (2003)
Performance Based Earthquake Engineering:PEER methodology
Damage Measure(s)
Predictable as a function of EDPs Full probability distribution function(s)
Event Summ ary Engineering Lesson s Learned : Structural Hazard Ass essment Future Trends
Performance Based Earthquake Engineering:
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Moehle (2003)
Performance Based Earthquake Engineering:PEER methodology
Decision Variable(s)
Tools for decision maker$ (owners, public policy officials)
Event Summ ary Engineering Lesson s Learned : Structural Hazard Ass essment Future Trends
Engineering Lessons Learned: Performance Based
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ATC-58 (2004)
Engineering Lessons Learned: Performance Based
Design
IO LS CP10
-5
10-4
10-3
10-2
10-1
100
Damage Measures (DMs)
MeanAnnualRateofExceedanceofDM
s
Seismic Demand Curve
2%, 50 yrs
20%, 50yrs
%10, 50 yrs
Replacement Cost
Event Summ ary Engineering Lesson s Learned : Structural Hazard Ass essment Future Trends
0 0.2 0.4 0.6 0.8 110
-5
10-4
10-3
10-2
10-1
100
Peak Horizontal Acceleration (PHA)
Mea
nAnnualRateofExceedanceofPHA
Seismic Hazard Curve
(% 50, 50 yrs)
(% 20, 50 yrs)
(%10, 50 yrs)
(% 2, 50 yrs)
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Engineering Lessons Learned: Geotechnical
Major lessons Damages in pipelines (water/gas) due to ground
deformation
Seismic compression of non-saturated engineering fills
Site response of deep soils/basin effects
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Ass essment Future Trends
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Engineering Lessons Learned: Geotechnical
Damage in water/gasdistribution systems
Damage correlated to Peak
Ground Velocity
(Jeong and ORourke, 2005)
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Ass essment Future Trends
G
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Engineering Lessons Learned: Geotechnical
Damage in water/gas distribution systems
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Ass essment Future Trends
Photos courtesyof J. Bray, UCB
E i i L L d G h i l
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Engineering Lessons Learned: Geotechnical
Seismic compression of non-saturated engineering fills Amount of damage to residential housing was large
Well documented case-histories (Stewart et al., 2004,
JGGE)
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Ass essment Future Trends
Source: Alan Kropp & David McMahon
Engineering Lessons Learned: Geotechnical/Ground
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g ee g esso s ea ed Geo ec ca /G ou d
Motions
Site response: clusters ofred-tagged buildings
Site response at deep soil sites
Basin effects
Observations led to changes in
the way site response is accounted
for
No similar changes yet for basineffects (too complex a problem)
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Ass essment Future Trends
Source: Davis et al. 2000, Science
Engineering Lessons Learned: Site Response in
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g g p
Codes
Before Northridge Zone Map
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Ass essment Future Trends
Courtesy of Jon Stewart, UCLA
Engineering Lessons Learned: Site Response in
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g g p
Codes
Before Northridge Zone Map
Linear PGA site
factors
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Ass essment Future Trends
Courtesy of Jon Stewart, UCLA
Engineering Lessons Learned: Site Response in
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g g p
Codes
Before Northridge Zone Map
Linear PGA site
factors
Site-dependent
spectral shapes
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Ass essment Future Trends
Courtesy of Jon Stewart, UCLA
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Engineering Lessons Learned: Site Response in
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Codes
After Northridge USGS online hazard
maps
Spectral shape
anchored at two
periods
Nonlinear site-
factors
New updates
proposed (Seyhan andStewart, 2014)
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Ass essment Future Trends
Courtesy of Jon Stewart, UCLASeyhan and Stewart 2014
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Engineering Lessons Learned: Ground Motions
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Engineering Lessons Learned: Ground Motions
Near-fault Ground Motions:Forward-directivity effects
Initiate with high-intensity-long-period pulses
Higher Peak Ground Velocity(PGV)
Higher level of spectralaccelerations within a narrowband
Shorter duration Higher damage potential
Event Summ ary Engineering Lessons Learned : Ground Motio nsHazard Ass essment Future Trends
Sommervile et al. 1997
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Progress in Seismic Hazard Assessmentin the last 20 years
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Progress in Seismic Hazard Assessment: Ground
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Motion Prediction
Ground motion prediction is key to seismic hazardassessment
Attenuation relationships, now called Ground Motion
Prediction Equations (GMPEs)
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Assessm ent Future Trends
Ground Motion Prediction
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Ground Motion Prediction
ProblemDetermine the ground motion parameters for a
hypothetical future earthquake scenario
Known Magnitude, distance, etc.
Since this is a prediction exercise, there is uncertainty
Prediction must be made in probabilistic terms
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Assessm ent Future Trends
Ground Motion Prediction
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1 2 10 20 1000.01
0.02
0.1
0.2
1
2
Distance from earthquake (km)
SpectralAcceleration,
(T
=
0.0
5
s)(g
)
Earthquakes of magnitude 7Earthquakes of magnitude 6
Ground MotionPrediction Equation(GMPE) or AttenuationRelationship
Courtesy of J. Bommer
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Assessm ent Future Trends
Ground Motion Prediction
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log(R)
M
log(Y)
, residual
log(Ypred)
log(Yobs)
Courtesy of J.Bommer
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Ground Motion Prediction Equations
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G ou d Mo o ed c o qua o s
Ground Motion Prediction Equations A function that predicts a ground motion parameters as a
function of Source, Site, and Geometrical parameters
log(Y) = f(M, F, R, S) + = f(M, F, R, S) + .
Ground Motion Parameter
Usually the log (natural log or base 10 log is taken because the
distribution is log-normal) Usually Y = Geometric Mean of Sa (T, x=5%), but can be anything
Duration, Tms, Arias Intensity, etc
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Assessm ent Future Trends
Ground Motion Prediction Equations
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q
Ground Motion Prediction Equations A function that predicts a ground motion parameters as a
function of Source, Site, and Geometrical parameters
log(Y) = f(M, F, R, S) + = f(M, F, R, S) + .
Median Prediction
This is the equation itself
In data rich regions: obtained fromregression analysis of recorded data
In CEUS, obtained from data andseismological simulations
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Assessm ent Future Trends
Ground Motion Prediction Equations
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q
Ground Motion Prediction Equations A function that predicts a ground motion parameters as a
function of Source, Site, and Geometrical parameters
log(Y) = f(M, F, R, S) + = f(M, F, R, S) + .
Deviation from median
s : standard deviation(predicted by the GMPE)
e: number of standard deviationsaway from the median
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Assessm ent Future Trends
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Progress in Seismic Hazard Assessment: Ground
Motion Prediction
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Motion Prediction
Since Northridge: large increase in available groundmotion data
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Assessm ent Future Trends
Courtesy of Jon Stewart, UCLA
Pre-Northridge Data
Progress in Seismic Hazard Assessment: Ground
Motion Prediction
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Motion Prediction
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Assessm ent Future Trends
Courtesy of Jon Stewart, UCLA
Since Northridge: large increase in available groundmotion data
Northridge Data
Progress in Seismic Hazard Assessment: Ground
Motion Prediction
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Motion Prediction
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Assessm ent Future Trends
Courtesy of Jon Stewart, UCLA
Since Northridge: large increase in available groundmotion data
NGA West II Data
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Progress in Seismic Hazard Assessment: GroundMotion Prediction
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Motion Prediction
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Assessm ent Future Trends
What is new?: Complexity!
Progress in Seismic Hazard Assessment: GroundMotion Prediction
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Motion Prediction
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Assessm ent Future Trends
NGA West 2 GMPEs capture: Magnitude range: 3 to 8.5 (for strike-slip events) Distance range: 0 to 300 km Hanging wall effects Site conditions: parameterized by Vs30 Term to capture deep site response (deep basin effect) Style of faulting term: strike slip, reverse, normal Magnitude saturation at short periods Buried ruptureeffects
Separate group working on Directivity effects (part ofNGA West 2 project)
Progress in Seismic Hazard Assessment: GroundMotion Prediction
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Motion Prediction
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Assessm ent Future Trends
NGA West 2 GMPEs capture: Magnitude range: 3 to 8.5 (for strike-slip events) Distance range: 0 to 300 km Hanging wall effects Site conditions: parameterized by Vs30 Term to capture deep site response (deep basin effect) Style of faulting term: strike slip, reverse, normal Magnitude saturation at short periods
Buried ruptureeffects
Separate group working on Directivity effects (part ofNGA West 2 project)
Progress in Seismic Hazard Assessment: GroundMotion Prediction
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Motion Prediction
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Assessm ent Future Trends
Magnitudesaturation is now a
common feature(from Y. Bozorgnia)
Progress in Seismic Hazard Assessment: GroundMotion Prediction
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Motion Prediction
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Assessm ent Future Trends
Buried Rupture M7 Surface Rupture
(from P. Somverville)
Progress in Seismic Hazard Assessment: GroundMotion Prediction
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Motion Prediction
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Assessm ent Future Trends
Period-to-Period correlation models Baker and Jayaram (2008), Baker (2011)
Progress in Seismic Hazard Assessment: GroundMotion Prediction
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Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Assessm ent Future Trends
Period-to-Period correlation models Baker and Jayaram (2008), Baker (2011)
Very useful for ground motion selection/assessment of
losses over a system with multiple components
NGA West 2: Period-to-Period correlation model will
be part of the final product
Progress in Seismic Hazard Assessment: Partiallynon-ergodic PSHA
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g
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Assessm ent Future Trends
Key to PSHA: accounting for uncertainties
Smalluncertainty
Largeuncertainty
Progress in Seismic Hazard Assessment: Partiallynon-ergodic PSHA
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g
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Assessm ent Future Trends
Two types of uncertainties
UNCERTAINTIES
ALEATORY EPISTEMIC
True randomness
(natural variability) Quantified by the
standard deviation (s) ofa probabilistic distribution
Cant be reduced with
more data
Lack of knowledge
Expert judgment Logic-trees
Can be reduced withmore data
Progress in Seismic Hazard Assessment: Partiallynon-ergodic PSHA
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g
Epistemic Uncertainty
Yucca Mountain Project(Stepp et al. )
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Progress in Seismic Hazard Assessment: Partiallynon-ergodic PSHA
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Sigma (aleatory variability) has remained constant over the
years, despite improved parameterizationFrom Strasser et al. (2009)
Progress in Seismic Hazard Assessment: Partiallynon-ergodic PSHA
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Why hasnt sigma decreased?
Some components of variability cant be reduced!
Within out limited parameterization (e.g., M, R, Vs30),
there is true natural variability
Improved characterization of some effects (hanging wall,directivity, etc):
Important in reducing bias
Does not reduce sigma because it affects only a limited portion
of the data
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Assessm ent Future Trends
Progress in Seismic Hazard Assessment: Partiallynon-ergodic PSHA
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However, one component of variability can bereduced: site-to-site variability
Variability that results from treating all sites with the
same parameterization (e.g., Vs30) as identical
Resulting variability is known as single-station sigma
For site-specific analysis, this variability can be
removed
At the cost of computing/measuring the averageresidual (e.g., the site term) at the given site
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Assessm ent Future Trends
Progress in Seismic Hazard Assessment: Partiallynon-ergodic PSHA
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0.01 0.1 0.2 0.3 0.5 1.0 3.00.2
0.4
0.6
0.8
Period (Sec)
ss
and
5.0
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0.01 0.1 0.2 0.3 0.5 1.0 3.00.2
0.4
0.6
0.8
Period (Sec)
ss
and
5.0
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Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Assessm ent Future Trends
Non-ergodic PSHA (e.g., use of single station sigmaUNCERTAINTIES
ALEATORY EPISTEMIC
Cant be reduced with
more data Can be reduced with
more data
PREDICTION OF SITE
RESPONSE
- Use generic predictive
variables
- Use measurements
- Site responseanalysis ($)
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What the future holds
Future Trends
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More NGA Projects (information below from Y. Bozorgnia, PEER) NGA West 3
Expand range of applicability of models into softer soil and
harder rock
Refinement of directivity models Improvement in prediction of vertical motions
Beyond elastic response spectra
Incorporate Single Station Sigma
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Assessm ent Future Trends
Future Trends
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More NGA Projects (information from Y. Bozorgnia,PEER)
NGA East for stable continental regions (2015)
NGA Subduction (2016)
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Assessm ent Future Trends
Future Trends
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Use of seismological models in hazard analyses Large scale validation project (SCEC)
Models already work well to predict median motions for
a low frequencies
At issue is how to predict input parameters for models
More applications of Single Stationconcept
Use of project-specific instrumentation to measure site
terms
Event Summ ary Engineering Lesson s Learned : Geotechnic al Hazard Assessm ent Future Trends
Concluding Remarks
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Research pays off Response to Northridge earthquake: Reaction from industry/funding agencies
Research
Code implementation
Civil engineering moving (fast) towards PerformanceBased Design
Important for insurance industry
Continued funding of research for seismic hazardreduction is important
Acknowledgments
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Matthew Eatherton (Virginia Tech) Jonathan Stewart (UCLA)
Julian Bommer (Imperial College)
Jonathan Bray (U.C. Berkeley)
Yousef Bozorgnia (U.C. Berkeley)
PEER (Northridge at 20 symposium)
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Thank you!