Charles R. Real: Charles R. Real: California Geological SurveyCalifornia Geological Survey

Anthony F. Shakal:Anthony F. Shakal: California Geological SurveyCalifornia Geological Survey

Brian E. Tucker:Brian E. Tucker: Geohazards InternationalGeohazards International

TURKEY FLAT, U.S.A. SITE EFFECTS TURKEY FLAT, U.S.A. SITE EFFECTS TEST AREA: ANATOMY OF A TEST AREA: ANATOMY OF A BLINDBLIND GROUND-MOTION PREDICTION TESTGROUND-MOTION PREDICTION TEST

Need to Validate Ground Motion Prediction Models

Theory

Data

Observation

Supposition Hypothesis

Measurement

Toward Knowledge

Experimentation

Model

ValidationSpecific Case

Background

• 1985 IASPEI/IAEE Resolution to:– Promote establishment of test sites around

world to validate methods of predicting “effects of surface geology on seismic motion”

– Form Joint Working Group to provide guidance for establishing test sites

• 1986 CGS/CSMIP established test site at Turkey Flat near Parkfield, CA

OverviewOverview

Rationale Site Selection/ Characterization Blind Tests Lessons Learned

Primary Goals of Turkey Flat Test

• Help evaluate state-of-practice in site response analysis

• Create observational database to facilitate site-response research

Objectives

• Validate current ground-motion models for shallow stiff-soil site

• Understand relative contributions to uncertainty: aleatory/epistemic….ground-motion model and site model

• Investigate potential non-linear behavior

Approach

• Conduct high-quality field and laboratory tests to characterize the geotechnical properties of the site

• Collect high-quality measurements of ground response in sediment basin and bordering rock

• Conduct test that emulates a typical engineering site response application

Design Rationale

• Emulate a common engineering application:– A typical construction site– A forward modeling approach (“blind” test)

• Simple site / abundant information– Geologically simple– Surface rock records

• Must have industry participation– Anonymity/confidentiality

-Dynamic Soil Properties

-Velocity Structure-Site Response =

-computational model

-Medium model

Uncertainty

A

A – surface rock to basement rock to surfaceB

B – basement rock through soil to surface

Understand Uncertainty• Statistics: Multiple teams

– Site characterization– Site response prediction

• Isolate two principal modeling steps:– Part A – uncertainty in predicting basement response

and how it affects estimated surface response– Part B – uncertainty in predicting soil response given

actual basement response

• Isolate variability due to computational & medium models– Compare results from “preferred” soil models against a

control model (“standard”)

MULTIPLE INVESTIGATION TEAMS

SITE CHARACTERIZATION•Field Surveys/Borehole logging•Laboratory Testing

SITE SELECTION•SSR Survey Profile•Seismic Refraction

WEAK-MOTION BLIND TEST•10 Countries•28 Teams

PART 1•29 “standard” model predictions•6 “preferred” model predictions

PART 2•20 “standard” model predictions•6 “preferred” model predictions

ARRAY INSTALLATION•Weak-motion (velocity sensors)•Strong-motion (accelerometers)

15Years

TURKEY FLAT SITE EFFECTSTEST AREA

STRONG-MOTION BLIND TEST•4 Countries•15 Teams

PART 1•25 “Standard” model predictions•20 “preferred” model predictions

PART 2•25 “standard” model predictions•22 “preferred” model predictions

MULTIPLEINVESTIGATION TEAMS

Experiment Timeline

Activity When

1. Site selection & characterization 1986

2. Accelerograph Installation 1987

3. Weak-motion data collection 1988-89

4. Weak-motion prediction test 1990

5. Strong-motion data collection ?

6. Strong-motion prediction test ?

Site Selection Criteria

• A geologically simple site

• Common site for construction

• A measurable site effect

• Strong-motion expected soon

1901

2004

1966

19341922

1881

1857

1800

1850

1900

1950

2000

2050

1 2 3 4 5 6 7

Parkfield Earthquake Series

Ye

ar

1985 Parkfield Earthquake Prediction Experiment

(M~6 by 1993)

Parkfield

San Francisco

ParkfieldParkfield

Parkfield

Turkey Flat

~2 km

D

½W= 1:40

View North

View South

Verification of Site EffectVerification of Site EffectSpectral RatioSpectral Ratio

Dashed: baseline site

Solid: 10m offset

Dotted: 20m offset

FieldTests

Lab Tests

Seismic Reflection

& RefractionSurveys

Cross-sections Through Test Area

R1, D1

V1, D2, D3

V2R2

B

B’

A

A’

C C’

Next slide shows profiles

Standard Model

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0.0001 0.001 0.01 0.1 1

Shear Strain (%)

G/G

max

Standard Model

0

2

4

6

8

10

12

14

0.0001 0.001 0.01 0.1 1

Shear Strain (%)

Dam

ping

(%)

Standard Velocity Model

0

5

10

15

20

25

30

0 200 400 600 800 1000 1200 1400 1600

Vs (m/sec)

Dep

th (

m)

Valley Center

Rock South

Rock North

Experiment Timeline

Activity When

1. Geotechnical site characterization 1986

2. Accelerograph Installation 1987

3. Weak-motion data collection 1988-89

4. Weak-motion prediction test 1990

5. Strong-motion data collection ?

6. Strong-motion prediction test ?

Accelerographs Installed

Weak-motion Data Collection

Weak-Motion TestWeak-Motion Test

30km

M2.0

Weak-Motion Test EventWeak-Motion Test Event

Weak Motion Test

Country Standard PreferredCanada 1 1China 2Czechoslovakia 2France 3 1Germany 1Italy 1 1Japan 7 2Mexico 1New Zealand 1USA 6 1

Totals 25 6

Weak-Motion Response SpectrumWeak-Motion Response SpectrumPredictions v.s. Observations

Solid: Test event

Dashed: Prediction Quartiles

(Cramer & Real, 1990)

Weak-Motion Spectral RatioWeak-Motion Spectral RatioPredictions v.s. Observations

Solid: Test event

Dashed: Prediction quartiles

Dot-dash: weak-motion events mean

Dotted: 1 of mean

(Cramer & Real, 1990)

Variability of Velocity StructureVariability of Velocity Structure

Solid: standard model

Dashed: Mean

Dotted: 2 intervals

Dash-dot: 2 of means

Bold: median used in simulations

(Field & Jacob, 1993)

Results of Sensitivity StudyResults of Sensitivity StudyMonte-Carlo Simulations

Solid: simulation median

Dashed: simulation inter-quartile range

Dotted: 90% simulation range

Dot-dash: standard model response

Bold: median of parameters

(Field & Jacob, 1993)

Insights From Weak-Motion Test

• Predictions tended to group…generally a success….

• Observations fall within range of expected uncertainties from modeling the site data

• Tendency to over-estimate amplitude… damping too low, velocity of surface layer

• Participants tended to underestimate uncertainty

Strong-Motion Test Timeline

Activity When

1. Geotechnical site characterization 1986

2. Accelerograph Installation 1987

3. Weak-motion data collection 1988-89

4. Weak-motion prediction test 1990

5. M6.0 Parkfield Earthquake 9/28/2004

6. Strong-motion prediction test 2005

M6.0

Test Site

Strong Motion Test EventStrong Motion Test Event

Strong-Motion TestStrong-Motion Test

Changes in Blind Test

• Require predictions based on “preferred” soil model

• Still have predictions based on “standard” soil model

• Request more time histories• Have two levels of participation:

– Volunteer– Funded

Required Strong-Motion Required Strong-Motion PredictionsPredictions

• Fourier Amplitude Spectral Ratios:– 1) Xi/R1 given R1 (where Xi means D1, D2, D3, V1,V2, R2)– 2) V1/D3, D2/D3 given D3

D3

D2

D1

R1V1 V2

R2

Two-step process: R1 predictions then D3 predictions

Required Strong-Motion Required Strong-Motion PredictionsPredictions

• Acceleration Time Histories:– (1) V1, D2, D3 given R1– (2) V1, D2 given D3

D3

D2

D1

R1V1 V2

R2

Required Strong-Motion Required Strong-Motion PredictionsPredictions

• Psuedovelocity Response Spectra (5% damped) & peak values displ, vel, accel:

– 1) Xi given R1 (where Xi means D1, D2, D3, V1,V2, R2)

– 2) V1, D2 given D3

D3

D2

D1

R1V1 V2

R2

Strong-Motion Prediction Teams

Italy 1Japan 4Republic of Czechoslovakia 1United States 9

Total Participants 15

82

SectorPart 1 Part 2

Total

Preferred Standard Preferred Standard

Industry 5 4 5 4 18

Academia 15 11 17 11 54

Government 5 0 5 0 10

 

Strong-Motion Prediction SetsStrong-Motion Prediction Sets

Industry 18

1-D Methods1-D MethodsMethod/Code

No. Sets

CategoryNo. Predictions1

Part 1 Part 2

SHAKE04 2 Equivalent Linear 0 4

SHAKE96B 4 Equivalent Linear 12 4

SHAKE91 8 Equivalent Linear 24 11

SHAKE72 4 Equivalent Linear 12 10

TremorKA 2 Equivalent Linear 6 2

TremorN2 2 Equivalent Linear 6 2

DeepSoil 12 Equivalent Linear/Nonlinear 24 12

FDM 4 Equivalent Linear 12 6

DMOD-2 6 Nonlinear Finite Element 4 10

RASCAL 4 Equivalent Linear 12 4

TESS 4 Nonlinear Finite Difference 7 4

PEXT 2 Linear Full Wave Propagation 6 6

Freq/Wavenmbr 1 Equivalent Linear 6 0

DYNEQ 4 Equivalent Linear 9 4

Subtotal (59) Subtotal (140) (79)

2-D/3-D Methods2-D/3-D Methods 

Method/CodeNo. Sets

CategoryNo. Predictions

Part 1 Part 2

2-D

NOAHW 2 Nonlinear Finite Difference 6 2

BESOIL 2 Equivalent Linear 6 2

SuperFLUSH 2 Equivalent-Linear Finite Element 6 2

Subtotal (6) Subtotal (18) (6)

3-D

FLAC 5 Nonlinear Finite Difference 4 6

OpenSees 4 Nonlinear Finite Element 5 4

SUMDES 4 Nonlinear Finite Element 4 4

Subtotal (13) Subtotal (13) (14)

EmpiricalSSR 2 Empirical 6 5

Subtotal (2) Subtotal (6) (5)

  Total 1,2 &3-D 802 Total 177 104

2Two additional prediction sets from averaging several codes

Workshop Timeline

Where When

1. Vancouver, B.C. 1987

2. Tokyo, Japan 1992

3. San Francisco, CASeptember 21,

2006

Turkey Flat WorkshopTurkey Flat Workshop(September 21, 2006)(September 21, 2006)

• Release observations at workshop

• Overview of observations/predictions– Predictions identified by team number only

• Expert panels:– Equivalent-linear methods– Nonlinear methods– Site Characterization

Lessons Learned

• More redundancy in site characterization

• Increase participation

• Require “standard” & “preferred” models

• Flexible submission formats

Potential Issues

• Considering proximity of Turkey Flat array to source rupture could observed motions be affected by finite source effects?

• Circa 1990 State-of-practice in site characterization?

Turkey Flat Working Group

www.quake.ca.gov/turkeyflat.htm

Individuals

Carl Stepp

C.Y. Chang

Neville Donovan

James Gates

I.M. Idriss

Fumio Kaneko

Marshall Lew

Saturo Ohya

Maurice Power

Bruce Redpath

Wolfgang Roth

J.P. Singh

John Vrymoed

William Joyner

Bill Iwan

Kazuyoshi Kudo

P.Y. Bard

Jon Stewart

Brian Chiou

Chris Cramer

Abbas Abghari

Ben Tsai

Steve Kramer

Ahmad Elgamal

Youssef Hashash

Geoff Martin

Yousef Borgzonia

Companies

Dames and Moore

Harding Lawson and Associates

Kajima Corporation

Lawrence Livermore National Laboratory

LeRoy Crandall and Associates

OYO Corporation

Pitcher Drilling

Qest Consultants

Woodward-Clyde Consultants

Land Owners – Donald and Nila McCornack