Discussion on
Seismic Site Response Characteristics in Korea

October 30th, 2012
@ Seogwipo KAL Hotel, Jeju Island, Korea

Sun, Chang-Guk
Korea Institute of Geoscience and Mineral Resources

Contents

Site Effects and Site Classification
Seismic Site Response in Korea
SummarySite Effects and Site Classification

Site Effects and Site Classification (1/5)

 Complexity of Earthquake Ground Motion
 Main Influence Effects• Source effects / Path effects / Site effects
 Geological Issue• Source represented by occurred earthquake characteristics
Rock • Path represented by attenuation relationship in rockoutcrop Geotechnical Issue : Site effects (sometimes included source & path)
SoilLocal Site
 Site effects
layers
Effects
Bedrock• The effects of near surface geologic and soil conditions• The effects of subsurface geometry and surface topography
Fault
movement

SourceEffects

PathEffects

PathEffects

Fault
movement

SourceEffects

Site Effects and Site Classification (2/5)

 Observational Evidence of Site Effects
 1994 Northridge Earthquake(Santa Monica; Gao et al., 1996)• The amplitudes at soil site are about 4 and 7 times stronger than those atrock site located apart from 650 m
Soil Site

Rock SiteSoildeposit
Rockformation

Site Effects and Site Classification (3/5)

 Determination of Site Coefficients, Fa and Fv Based on
1989 Loma Prieta and Other Earthquakes
Short-period
Site (amplification) coefficient (Fa)Mid-period
Site (amplification) coefficient (Fv)

Rsoil 1 0.5 RS soil (T )Fa dT
0.1
Rrock 0.4
RSrock (T )Rsoil 1 2.0 RS soil (T )Fv dT
0.4
Rrock 1.6
RSrock (T )Intermediate-period
Site (amplification) coefficient (Fi)

Rsoil 1 1.5 RS soil (T )Fi dT
0.5
Rrock 1.5
RSrock (T )Long-period
Site (amplification) coefficient (Fd)

Rsoil 1 5.0 RS surface (T )Fd dT
1.5
Rrock 3.5
RSbedrock (T )

Sites were classified based on
the mean shear wave velocityof the upper 30m(Vs30; 100ftor 30.48m) depth.
ndii 1 VSi

VS 30  30 / Basis of the Current
Site Classification System

Site Effects and Site Classification (4/5)

 Current Site Classification System for Seismic Design(UBC 1997; NEHRP 1997; 2000)
Average Soil Prop

SA (Site Class A)
SB (Site Class B)

SC (Site Class C)
SD (Site Class D)
SE (Site Class E)

2.5Ca
GenericDescription

Spectral Acceleration (g)Soil Profile Type

Mid-Period

Z = 0.11 Z = 0 07 Z =0.11 Z = 0.07(m/s)TSC= Cv/2.5Ca
Vs (Vs30)
Fa Ca Fa Cv Fv Cv Fv
aCv/T
T0 = 0.2TS
0.09 0.82 0.05 0.71 0.09 0.82 0.05 0.71
> 1,500

Hard RockRock760 - 1,500

0.11 1.00 0.07 1.00 0.11 1.00 0.07 1.00

VeryCaDense andSoft Rock360 - 760

0.13 1.18 0.08 1.14 0.18 1.64 0.11 1.57

Stiff Soil

180 - 360

0.16 1.45 0.11 1.57 0.23 2.09 0.16 2.29

Soft Soil< 180

0.22 2.00 0.17 2.43 0.37 3.36 0.23 3.29

T0
SF (Site Class F)

Short-PeriodTSPeriod(sec) Site-specific Evaluation
Soil Requiring

Site Effects and Site Classification (5/5)

 Determination of Response Spectrum for Seismic Design
Determination of Design
Response Spectrum
Determination ofSeismic Coefficients(Ca, Cv )Determination ofSeismic Zone

INCONSISTENTIn the Korean Sites

Determination of Site
Response Spectrum
Quantification ofSite Amplification

Categorization of
Soil Profile Type( Korean Guide based on
NEHRP and UBC )Rockoutcropping
motionfor design

Surface motion resulting
in hazard analysis

Soil profileat site ofinterest
Bedrock motion

Earthquake
by Fault Movement

Attenuation withgeological distance

Site
Response
Analysis

Seismic Site Response in Korea

Seismic Site Response in Korea (1/6)

 Vs Profiles in Korea andWestern US (WUS)
Shear Wave Velocity, Vs (m/s)
030060090012000030 m ≈ 100 ft

202500TS01 (5m)TS02 (DT 110m)
TS03 (DT 153m)
TS04 (DT 88m)
TS05 (DT 287m)

Site Class C

401500

Shear Wave Velocity, Vs (m/s)
0Shear Wave Velocity, Vs (m/s)
500
1000
1500
2000

0200400

Site Class D

TS06 (139m)
TS07 (83m)
TS08 (DT 92m)

Shear Wave Velocity, Vs (m/s)

600

800

1000

00200

400

600

80001000

diVSi

5Mean Vs to 30 m (Vs30)
of soil deposit in Korea(Site Class C; 448.6 m/s)

Mean Vs to 30 m (Vs30)
of soil deposit in Korea(Site Class D; 346.9 m/s)

10WUS

TS11 (55m)
TS12 (DT 25m)
TS13 (9m)
TS14 (DT 240m)
TS15 (DT 64m)
TS16 (DT 97m)
TS17 (DT 103m)

10TS18 (DT 108m)

10Korea

15Mean Vs to 30 m (Vs30)
of soil deposit in WUS(Site Class C; 510.0 m/s)

20

TS09 (59m)
TS10 (15m)

Mean Vs to 30 m (Vs30)
of soil deposit in WUS(Site Class D; 304.3 m/s)

TS19 (DT 97m)
TS20 (49m)
TS21 (158m)
TS22 (32m)
TS23 (25m)
UG01 (81m)
UG02 (DT 87m)

20UG03 (80m)

20Boundary of Vs30to Classify
Site C and D(360.0 m/s)

30

WUS

Depth (m)Korea

Depth (m)Depth (m)UG04 (DT 90m)

25

UG05 (DT 90m)
UG06 (43m)
UG07 (DT 90m)
UG08 (DT 90m)
UG09 (73m)

30

UG10 (DT 75m)
UG11 (DT 354m)

30Boundary of Vs30
to Classify
Site C and D(360.0 m/s)

35

UG12 (DT 264m)
UG13 (DT 342m)
UG14 (238m)
UG15 (DT 89m)
UG16 (DT 57m)

40

UG17 (DT 88m)
UG18 (DT 87m)
40455040

Korea; Average

Korea; Average + Standard Deviation

Korea; Average + Standard Deviation

UG21 (11m)

Korea; Average - Standard Deviation

Korea; Average - Standard Dev ation

UG22 (DT 89m)

WUS; Average

WUS; Average

UG23 (13m)

WUS; Average + Standard Deviation

WUS; Average + Standard Deviation

UG24 (DT 90m)

WUS; Average - Standard Deviation

WUS; Average - Standard Deviation

Ave of Site Class E

UG20 (12m)

UG25 (DT 29m)
UG26 (DT 318m)

505055

UG19 (DT 99m)

Korea; Average

360

Average of WUS
Average of Korea

Seismic Site Response in Korea (2/6)

 Distribution of Site Period (TG)nDii 1 VSi

TG  4

0.045

Site Class C of Korea (36 Sites)
Site Class D of Korea (24 Sites)
Site Class C of WUS (15 Sites)
Site Class D of WUS (34 Sites)

0.010

Probability Density in Korea

0.040

Lognormal Probability Density

0.005

0.035
0.030
0.025
0.020
0.015
0.010
0.005

0.004

0.008
0.003
0.006
0.002
0.004
0.001

0.002

0.000

Probability Density in Western US

0.012

0.0All Sites
Site Class C
Site Class D

3.0

0.000

0.000
0.0

0.5

1.0

1.5
2.0
Site Period, T G (sec)

2.5

3.0

Somewhat different for C sites; Significantly different for D sites

3.5

Seismic Site Response in Korea (3/6)

 Response Spectra from Analyses
0.80

Site Class B (Rock-outcrop 0.14g)

Spectral Acceleration (g)Average of B sites(CLE, damping = 5%)

Average + 

0.60

Average
Average - 

0.40

Design for B site
0.20

0.00
0.01

0.1

110

• In C and D sites, the spectral
accelerations of response spectra aresignificantly higher than those ofdesign spectra near resonant periods.
• The resonant periods of D sites are
longer than C sites.

Period (sec)

1.40Site Class C (Rock-outcrop 0.14g)

1.40

1.20

Site Class D (Rock-outcrop 0.14g)
Average of D sites(CLE, damping = 5%)

Average of C sites(CLE, damping = 5%)

Average + 

1.20

Spectral Acceleration (g)Spectral Acceleration (g)Average + 
1.00

Average
0.80

Average - 
0.60

Design for C site
0.40

0.20

Average

1.00

Average - 

0.80

0.60

Design for D site
0.40

0.20

0.00

0.00
0.01

0.1

1
Period (sec)

10

0.01

0.1

1
Period (sec)10

Seismic Site Response in Korea (4/6)

 Average of Response Spectra
CLE (Rock-outcrop 0.14g)
Averages of Each Site Class(CLE, damping = 5%)

Spectral Acceleration (g)1.20

Range of Site Period
in Korea

1.00

0.80

Short-Period

0.60

Response Spectrum of D site
Response Spectrum of C site
Response Spectrum of B site
Design Spectrum for E Site
Design Spectrum for D Site
Design Spectrum for C Site
Design Spectrum for B site

OLE (Rock-outcrop 0.05g)
Averages of Each Site Class(OLE, damping = 5%)

0.50

Spectral Acceleration (g)1.40

Mid-Period
0.60

0.40

Range of Site Period
in Korea

0.40

Short-Period

Response Spectrum of D site
Response Spectrum of C site
Response Spectrum of B site
Design Spectrum for E Site
Design Spectrum for D Site
Design Spectrum for C Site
Design Spectrum for B Site

0.30

Mid-Period

0.20

0.10

0.20

0.00

0.00
0.01

0.1

1
Period (sec)100.010.1

1Period (sec)• Maximum spectral accelerations of C and D sites are higher,
respectively, than those of design spectrum for site classes D and E,
near resonant period.

10

Seismic Site Response in Korea (5/6)

 Ratio of Response Spectra
4

Average (CLE; 0.14g)
Fa on code (CLE; 0.14g)
Fv on code (CLE; 0.14g)
Average (OLE; 0.05g)

Ratio of Response Spectra, RRS

Average of C Sites(CLE)

Average + 

3Average
Average - 21 In site class C in Korea• Fa on current code issignificantly underestimated.
• Fv on current code isconsiderably overestimated.

00.00.5

4

Ratio of Response Spectra, RRS

Average of D Sites(CLE)

1.0Period (sec)

Average + 
Average31.52.0

Average (CLE; 0.14g)
Fa on code (CLE; 0.14g)
Fv on code (CLE; 0.14g)
Average (OLE; 0.05g)

 In site class D in Korea• Fa on current code isunderestimated.
• Fv on current code isconsiderably overestimated.

Average - 
2

10
0.0

0.5

1.0
Period (sec)

1.5

2.0

Seismic Site Response in Korea (6/6)

 Site Coefficients According to Vs30
4Short-Period Site Coefficient, Fa

Fa = 199.05 Vs30 -0.78(OLE; 0.05g)

Fa vs Vs30 (CLE; Analyses 0.14g)
Fa vs Vs30 (OLE; Analyses 0.05g)
Fa vs Vs30 (CLE; Code 0.14g)
Fa vs Vs30 (OLE; Code 0.05g)

32

Fa = 97.07 Vs30 -0.66(CLE; 0.14g)

 In Fa for short-periods in Korea• Fa ranging 1.0 to 2.7 are larger
than those on current code.

1

Fa = 130.30 Vs30-0.71(Representative Regression based on all data)
00300

600
900
1200
Mean Shear Wave Velocity to 30m, Vs30 (m/s)

1500

4Fv vs Vs30 (CLE; Analyses 0.14g)

 Site Coefficients, Fa and Fv, show
similar values, regardless of rockacceleration levels of CLE and OLE.

Mid-Period Site Coefficient, Fv

Fv vs Vs30 (OLE; Analyses 0.05g)
Fv = 7.46 Vs30
(CLE; 0.14g)

3

Fv vs Vs30 (CLE; Code 0.14g)-0.30

Fv vs Vs30 (OLE; Code 0.05g)

2

Fv = 5.25 Vs30
(OLE; 0.05g)

 In Fv for mid-periods in Korea• Fv ranging 1.0 to 1.6 are smaller
than those on current code.

-0.25

1

Fv = 5.63 Vs30-0.26(Representative Regression based on all data)
00300

600900Mean Shear Wave Velocity to 30m, Vs30 (m/s)

1200

1500

Summary Site characterizations in Korea were performed to evaluate the seismic site
response characteristics, and the following conclusions were obtained: Depth to bedrock  Korea << WUS
Soil stiffness  Korea > WUS
 Site period  Korea (0.1 to 0.4 sec) << WUS (0.2 to 1.8 sec)
 Spectral acceleration in response spectra from site response analyses
 Analyses for C and D sites in Korea > Design code (near the site periods)

 Site coefficients, Fa & Fv, from site response analyses
 Fa (1.0 to 3.0) in Korea > Fa in Design code Fv (1.0 to 1.5) in Korea < Fv in Design code

Thank You !!