January 18, 2002 2002 PEER Annual Meeting

PPEEEERR

Jonathan P. StewartUniversity of California, Los Angeles

Graduate Students: Yoojoong Choi and Andrew Liu

Site Categories and Amplification Factors

2002 PEER Annual Meeting

Context

( ) ∫∫ >×∑== mr

N

ii dmdrrmzIMPrfmfIM

flt

),|()()(1υυ

Conventional PSHA (Cornell, 1968):

Attenuation RelationshipDerived from PDF f(IM|m,r,…)Described by: - median

- standard deviation

2002 PEER Annual Meeting

Attenuation Relations

• Tectonic regime

• m, r

• Focal mechanism

• Site condition

Factors affecting attenuation of Sa:

- Broad site categories

2002 PEER Annual Meeting

Amplification Factors

• Used to adjust moments of attenuation relation• Reference site approach

– e.g.: Idriss, 1990; Borcherdt and Glassmoyer, 1994; Borcherdt, 2002

– Azimuth and distance corrections

– Derived error term

2002 PEER Annual Meeting

Amplification Factors

• Non-reference site approach– Amplification taken as residual from

attenuation relation

– e.g.: Sokolov, SCEC, this study– Azimuth corrections, event terms– Direct error terms

( )ijrijij SSTF =)(

2002 PEER Annual Meeting

Classification Schemes

• Surface geology

Age Depositional Environment Sediment TextureHolocene Fan alluvium Coarse

Pleistocene Valley alluvium FineLacustrine/marine Mixed

AeolianArtificial Fill

TertiaryMesozoic + Igneous

Table 3.2. Criteria for surface geology classifications

2002 PEER Annual Meeting

Classification Schemes

• NEHRP/VS-30

NEHRP Category Description

Mean Shear Wave Velocity to 30 m

A Hard Rock > 1500 m/sB Firm to hard rock 760-1500 m/sC Dense soil, soft rock 360-760 m/sD Stiff soil 180-360 m/sE Soft clays < 180 m/sF Special study soils, e.g., liquefiable

soils, sensitive clays, organic soils, soft clays > 36 m thick

Table 3.3. Site categories in NEHRP Provisions (Martin, 1994)

Reference: Martin (1994)

2002 PEER Annual Meeting

Classification Schemes

• Geotechnical

data

Site Description Approx. Site

Period (s)

Comments

A Hard Rock ≤ 0.1 ; Crystalline Bedrock Vs ≥ 1500 /m sB Competent Bedrock ≤ 0.2 Vs ≥ 600 / < 6 . “ ” m s or m of soil Most unweathered

California Rock cases1C Weathered Rock ≤ 0.4 Vs ≈ 300 / > 600 / , m s increasing to m s weathering

> 6 < 30 zone m and m2C Shallow Stiff Soil ≤ 0.5 > 6 < 30 Soil depth m and m3C Intermediate Depth Stiff

Soil ≤ 0.8 > 30 < 60 Soil depth m and m

1D Deep Stiff Holocene Soil ≤ 1.4 > 60 < 200 Depth m and m

2D Deep Stiff PleistoceneSoil

≤ 1.4 > 60 < 200 Depth m and m

3D Very Deep Stiff Soil ≤ 2.0 > 200 Depth m1E Medium Thickness Soft

Clay ≤ 0.7 3-12 Thickness of soft clay layer m

2E Deep Soft Clay ≤ 1.4 > 12 Thickness of soft clay layer mF Potentially Liquefiable

Sand (Holocene loose sand with high water table zw ≤ 6 )m

Reference: Rodriguez-Marek et al. (2001)

2002 PEER Annual Meeting

This Study

• Large strong motion database• Leverage new geologic data sources

– CDMG mapping– Borehole and geophysical data (e.g.,

ROSRINE)

• Reference motions from Abrahamson and Silva (1997) rock attenuation– Directivity correction– Event term correction

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Data Resources

• Strong motion data– PEER data set (1032 recordings from 51 eqks), up to

1999 Duzce, Turkey event

• Site classifications– Surface geology

• 460 age only

• 240 age + depositional environment

• 168 age + material texture

– NEHRP, 185 sites

– Geotechnical data, 183 sites

2002 PEER Annual Meeting

Interpretation of Results

Data Regression• • Evidence of nonlinearity

– Hypothesis testing– b-value departs from zero

by more than its estimation error

• Distinction between categories– F-test

Holocene (all)

)ln()ln( ijiiij GbaF +=

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Holocene Pleistocene

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Discussion of Results

• Effect of period

• Distinct categories for each scheme

• Comparison to previous studies

• Inter-category error– Measure of relative effectiveness of

classification schemes

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Effect of Period

HoloceneAge-only

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Surface Geology

Holocene lacustrine/marine Quaternary alluvium

TertiaryMesozoic + Igneous

Age + DepositionalEnvironment

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Surface Geology

Holocene Coarse Holocene Fine

Age + Material Texture

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NEHRP

B

C D

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Geotechnical Data

B C

D E

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Comparison

C

D

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Comparison

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Inter-Category Error Terms

• Individual residual

• Category residual

• Scheme residual

• Inter-category error

∑=

=M

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MR

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preijdataijij FFR )ln()ln( −=

2002 PEER Annual Meeting

Results: “Soil” Categories

2002 PEER Annual Meeting

Final Remarks

• Desired features of classification schemes:– Minimize dispersion (detailed geology)– Categories have distinct amplification levels

(NEHRP)

• Amplification factors smaller than design standards

• Further improvements require consideration of basin geometry