peer jonathan p. stewart university of california, los angeles graduate students: yoojoong choi and...
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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 =)(
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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
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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
2002 PEER Annual Meeting
Inter-Category Error Terms
• Individual residual
• Category residual
• Scheme residual
• Inter-category error
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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