The 1st Annual Meeting of the Project of Seismic Hazard Assessment for the Next Generation Map:
Strategic Japanese-Chinese-Korean Cooperative Program

Seismic Attenuation in the Korean Peninsula
Seismic Parameters forPrediction of Strong Ground Motions in Korea

Tae-Seob Kang1, Nam-Dae Jo2 & Chang-Eob Baag3
1Department of Earth Environmental Sciences, Pukyong National University, Korea
2Daewoo International Corporation, Korea

3School of Earth and Environmental Sciences, Seoul National University, Korea

27 November 2011, Harbin Institute of Technology

Contents
1. Basic Definition on Earthquake Ground Motions
2. Efficient Procedure for Estimation of SeismicParameters for Ground Motions

1. Basic Definition on Earthquake
Ground Motions

“By Any Other Name”
Attenuation laws (Europe)
Attenuation relations (U.S. Engineers)
Attenuation relationships (U.S. Engineers)
Attenuation equations
Ground motion relations (U.S.
Seismologists)
Ground motion prediction relations
Ground motion prediction equations
Ground motion estimation equations

Definition“An attenuation law is a mathematical equationor engineering model that relates a strongmotion parameter to one or more parameters ofthe earthquake source, wave propagation path,and local site conditions”

Methods of Development
Empirical methods

Derived from strong-motion recordings

Hybrid empirical methods

Derived by modifying empirical attenuation laws in one
region to use in another region based on seismologicaltransfer functions usually derived using stochasticmethods (see below)

Stochastic methods

Derived from stochastic ground-motion simulations
and simple seismological models

Theoretical methods

Derived from kinematic and dynamic ground-motion
simulations and rigorous seismological models

Basic Functional Formlog Y = c1 + c2M – c3 log R – c4R + a + ewhere,log Y= log of strong-motion parameter
M= earthquake magnitude or (M)R = source-to-site distance or (R,M)
a= aleatory uncertainty
e= epistemic uncertainty
ci = model coefficientsCommon Parameters
Ground-motion measure
Earthquake magnitude
Source-to-site distance
Finite faulting effects
Local site conditions
Stress drop
Hanging-wall effects
Tectonic environment

2. Efficient Procedure for
Estimation of Seismic Parameters
for Ground Motions

Seismic parameters forcomputation of ground motions
Source parameters
Seismic moment (M0), Corner frequency (fc ), Stress drop ()log ( Disp )log ( Accel )~ M0log f
fc

tlog ffc

tePropagation constants
Quality factor Q (q ), site-dependent s, Geometrical spreading R-A ( f , R )  e   f  R     qR   ssite-specific parameterregional parameter (~ Q )

 s1
 s5

 s6

Q and 
 s4

 s3

 s2

-values from acceleration spectrum
37.5N

Fourier Amplitude Spectrum of Acceleration

Magnitude

1999/06/02

2.0
3.0
4.0

UJA

KRA station R = 58.0 km

1FAS (cm/sec)

37N

LATITUDE

36.5N

0.1

0.01

EW
0 001
01020

Frequency (Hz)304036N
GKP

WSC

TAG

Log(FAS) = -0.126045 f - 0.132014

WSA
WSB
WSN f

35.5N
KRA
KRB
KOR

PUS

35N
127.5E

128E

128.5E129E

LONGITUDE

129.5E

130E

 RKRA58 km  0.0401

Linear curve fitting for  = s+qR
0.08

kappa

0.06
0.04?

0.02
0-0.02010 20 30 40 50 60 70 80 90 100 110 120

Hypocentral distance (km)-value; May be seriously influenced by the site effect Need to propose a new procedure for s and qComputation of site-dependent 
1st STEP: computation of site independent value q (or Q )Using coda normalization method (Frankel, 1990) or others
tc =85.7 sec (2Ts120 for R=120 km)
Ts58
Origin time

S window

Coda window

EW

1999/06/02

KRA station R = 58 km

Result of inversion for Q and  = 0.7649
Q = 2022.58
 q = 0.0001413; slope in -R relation
is obtained

slope = qs =  s + q RR

computation of s for each siteusing given q value

0.08

0.08

0.060.06

kappa

0.04
0.02

0.04
0.02
00-0.02

0.08

WSA-0.02

0.06

KRA
0 10 20 30 40 50 60 70 80 90 100110120

0 10 20 30 40 50 60 70 80 90 100110120

Hypocentral distance (km)Hypocentral distance (km)
0.08

0.08

0.06

0.06

kappa

kappa

2nd STEP :

0.04
0.02
0kappa

kappa

-0.02
0.04
0.02

0 10 20 30 40 50 60 70 80 90 100110120

0.04

Hypocentral distance (km)0.02
00-0.02

All data

TAG

-0.02

GKP
0 10 20 30 40 50 60 70 80 90 100110120

0 10 20 30 40 50 60 70 80 90 100110120

Hypocentral distance (km)Hypocentral distance (km)Station

WSA

WSB

WSC

WSN

KRA

KRB

KOR

UJA

TAG

GKP

PUS

s

0.02647

0.013370.01732

0.028850.03300

0.015130.02577

0.03588

0.002665- 0.01087

0.01302

Site-dependent s values
37.5N

0.03588

UJA

37N

LATITUDE

36.5N

0.01732

36N

0.002665

GKP

WSC

TAG

-0.01087

WSA
WSB

0.01338

35.5N
KRA

0.01513

KRB
KOR

PUS

35N
127.5E

128E

128.5E129E

LONGITUDE

WSN

0.02647
0.02885

0.033
0.02577

0.01302129.5E

130E

Brune’s stress droplog (Disp)log (Disp)

0
Conversion by  -value

log f

log ffc
Data spectrum

Stress drop () is obtained fromLow frequency spectral value (0)• Corner frequency (fc)•

Source spectrum

1999 Gyeongju Earthquakes, Korea
Three small-to-medium-sized earthquakes at almost thesame location
Mw
4.0
3.8

1999/04/24

3.4

1999/09/12
1999/06/02

3.1
3.0

Time

Jan. 1, 1999
Apr. 2435.847N
129.266E

Dec. 1, 1999
Jun. 235.847N
129.266E

Sep. 1235.852N
129.258E1E-001

1E-001

1E-002

1E-002

1E-002

1E-003
1E-004
1E-005FD (cm-sec)

1E-001FD (cm-sec)

FD (cm-sec)

Computed source spectrum(smoothed)

1E-003
1E-004
1E-005

Jun. 2, 1999

1E-006

Sep. 12, 1999

1E-006
10Frequency (Hz)1E-004
1E-005

Apr. 24, 1999
1

1E-003100

1E-006110

Frequency (Hz)

100

110

Frequency (Hz)100

Computed source parameters100

Low-frequency spectral level99-barStress drop

900.1

Weighted average
78-bar

80
0.01

7060

0.001

0.0001
3

1232

3.4

Mw3.63.84

 (bar)0 (cm • sec)

15048-bar4044-bar

30

Corner frequency

20

10fc (Hz)

1080
63

3.2

3.4

3.6

3.8

4

Mw

420332

3.4

Mw

3.6

3.8

4

Mw=3.1

Mw=3.4

Mw=3.8Apr. 24

Sep. 12Jun. 2

Conclusion
Proposed methods and procedures forestimation of site-dependent groundmotions can be efficiently used in the low
and moderate seismicity regions.