AssessingAi Nonlinear
N liBehavior
B h i off Soils
S il ini
Seismic Site Response:
Statistical Analysis of KiK-net
Strong-Motion
Sto g ot o Dataata
Julie Régnier1, L.F. Bonilla2, E. Bertrand1 & J.F. Semblat2

1 CETE Méditerranée, laboratoire de Nice
2 IFSTTAR, Marne-la-ValléeTokyo, the 25th of september 2013

Introduction
Non-linear soil behaviour: strong impact on site response
1- Example with Tohoku recordings
Even for moderate events:
2- Statistical analysis on all KiK-net sites
What are the effects on site response?
pWhat are the pertinent parameters to predict such behavior?
3- Statistical analysis on 54 KiK-net sites
Æ Need to take this phenomenon into accountE
Especially
i ll iin llow seismicity
i i it areas?
?
Numerical simulations. But, first we need site characterization/ expensive tests:

What is the depth
p until which this characterization isrequired ?
4- Inversion of non-linear site response21- Example with Tohoku recordings
Non-linear soil behaviour : strong impact on site response
Comparison of site responses (Fourier spectral ratios on borehole data)
Tohoku main event versus aftershocks at 4 KiK-net sites

406080Vs ((km/s))
602050Boorehole response

Depth (m)•3020100•4008025006060

1360

IBRH11 Vs30= 242 m/s

10100

400

Boreholee response

Deptth (m)20Vs (km/s)
1 2 34030
20060

IBRH16 Vs30= 626 m/s

4030
20100IWTH21 Vs30= 521 m/s

5010Boorehole response00

Boreholee response••MYGH04 Vs30= 850 m/s

5040302010510 15 20Frequency (Hz)25300510 15 20Frequency (Hz)2530

Shift of the amplification peak toward low frequenciesÆIncrease amplification at low frequencies !!!
Decrease of the amplification at high frequencies

32- Statistical analysis on all KiK-net sites
Non-linear soil behaviour : strong impact on site response evenfor moderate events••

Comparison of site responses (Fourier spectral ratios on borehole data)
For all events we calculated: PNLev (%) Percentage of non-linearity:Frequency (Hz)4

2- Statistical analysis on all KiK-net sites
Non-linear soil behaviour : strong impact on site response evenfor moderate events••

Comparison of site responses (Fourier spectral ratios on borehole data)
For all events we calculated: PNLev (%) Percentage of non-linearity:

A1

Frequency (Hz)52- Statistical analysis on all KiK-net sites
Non-linear soil behaviour : strong impact on site response evenfor moderate events••

Comparison of site responses (Fourier spectral ratios on borehole data)
For all events we calculated: PNLev (%) Percentage of non-linearity:

A1
PNLev=A1

A2

A2

Frequency (Hz)6

2- Statistical analysis on all KiK-net sites
Probability PNLev > 10%: NL ≠ linear site response ?
PGA > 75 cm/s2 at depth ≈ PGA > 150 cm/s2 at the surface
P ≥ 40% Whatever the site!!
Probabilityy of having
g largeg modification linear/non-linear
site response is high even for moderate EQ
French seismic zonation(22 octobre 2010)
Agr
Very weak
Weak

70 cm/s2

moderate

110 cm/s2

Medium160 cm/s2

strong300 cm/s2

http://www.planseisme.fr/Zonage-sismique-de-la-France.html

3- Statistical analysis on 54 KiK-net sites
Sites selection• 54 sites• 2 EQ
PGA >50 cm/s2(downhole)• Variability
Vs30 OK8

3- Statistical analysis on 54 KiK-net sites
Per site : definition of fNL
Linear to non-linear site response ratio
Field et al (1997)

fNL frequency from which the ratio is >1

f>fNL
BFSRlin > BFSRstrong
f<fNL
BFSRlin < BFSRstrong

Fréquence (Hz)93- Statistical analysis on 54 KiK-net sites
Correlation fNL with soil and site response parameters• f0 : Funadamentalqy H/Vresoance frequency:surface• Apred : Maximal amplitude
off theth mean linearlisiteit
response BFSR
• Fpred : Assoicatedfrequency to ApredApredf0

fpred

3- Statistical analysis on 54 KiK-net sites
Correlation fNL with soil and site response parameters
fNL ≤ fpred

fNL (Hzz)fNL ≥ f0

fNL between f0 et fpred :Æ HF more affected by NL soil behaviour
Æ NL takes mostly place in the soil layers linked to HF amplifications
Æ Shallow layers

113- Statistical analysis on 54 KiK-net sites
These observations suggest• fNL between f0 et fpred : NL take mostly place in shallow soil layers?
• Measure of NL soil properties enough in the shallow soil layers tocharacterize the whole soil column NL response?
•Quantification of the depth where it occurs mostly?

• Use of inversion techniques: Inverting the site response to recoverqVs pprofile : Weak motion versus strongg motion
the equivalent124- Inversion of linear/non-linear site response
Approach

Adjusting theelastic Vs(z)Linear site response

Comparison
Vs inversionlinear / NL

Inversion

finding thei lV
Vs(z)
( )
equivalentfor strong
deformation

Non-linear response

IInversion
i13

4- Inversion of linear/non-linear site response
Site selection criteria: - 1-D site configuration,- with weak and strong motion recordings

Comparison empiricaland numerical linear
site
i responses

Comparison empiricallinearea aandd non-linearoea
site responses

14

4- Inversion of linear/non-linear site response
Vs adjustement
Best solution from inversion : layer 3 deeper

in agreement with geological log

15

Inversion non-linear response
Parametrization & initial model•

Depth of soil layers fixed from linear inversion•Vs intervals from linear inversion CV = 60 %•Test on 3 EQs

EQMjma

Depi

DepthPGAsurf

KmKm

cm/s2

1

9202

24372

2

7.1

28

10128

3

6.3

24

10110
16

Inversion non-linear response

Z (mm)% off ddecrease off VVs comparedd tto elastic
l ti properties
ti
EQ 1

EQ 2

EQ 3

PGAsurff

372

128

110

Vs11504316

Vs2150

4316

Vs3

31

1320

Vs4

230.02

0.02

Vs5---•EQs 2 et 3 : layers 1, 2 et 3 affected•

EQ 1: layers 1, 2, 3 et 4 affected

17Inversion non-linear response

Z (mm)% off ddecrease off VVs comparedd tto elasticl ti properties
ti
EQ 1

EQ 2

EQ 3

PGAsurff

372

128

110

Vs1

150

4316

Vs2

150

4316

Vs3

31

1320

Vs4

23

0.02

0.02

Vs5---•

EQs 2 et 3 : layers 1, 2 et 3 affected•

EQ 1: layers 1, 2, 3 et 4 affected

Superficials layers more affected during the 3 Eqs
Deeper layers affected during the strongest
18Conclusions
Non-linear soil behaviour effects on site response:Æ Decrease of amplification at high frequency
Æ Amplification
A lifi ii
increase
at lowlfrequencies
fi

Probability of having large modification linear/non-linear
site response is high even for moderate EQ (PGA>150 cm/s2)
Site-specific analysis showed that NL soil behaviour:Æ Occurs on superficial soil layers
Æ Depth also depends on incident motion intensity
In accordance with previous studies:Æ Regnier et al 2013: Statistical analysis on 54 KiK-net sites
Æ Aguirre and Irikura (1997): Vs reduction in the second layer between 5 m to 16 m depth
Æ Pavlenko and Irikura (2006) Soil nonlinearity in the upper 15-25 m of the soil profiles
Æ De Martin et al. (2010) Vs reduction occurred mostly around 35 m depthÆ Assimaki and Li (2012), showed that Vs30 (superficial soil parameter) was a relevant
parameter to analyze non-linear site responses

19Thanks for your attention!!!

Bonilla, L. F., Tsuda, K., Pulido, N., Regnier, J., & Laurendeau, A. (2011). Nonlinear site response evidence of K-net andKiK-net records from the Mw 9 Tohoku earthquake. Earth Planets Space, 58.
Régnier, J., Cadet, H., Bonilla, F.-L., Bertrand, E., Semblat, J.-F. (2013-a) Assessing nonlinear behavior of soils inseismic site response: Statistical analysis on KiK-net strong motion data. Bulletin of Seismological Society of America,
accepted in february 2013, Volume 103, Issue 3.
Régnier JJ., Bonilla,
Régnier,
Bonilla F
F.-L.,
L Bertrand
Bertrand, EE., Semblat
Semblat, JJ.-F.
F Influence of the velocity profile at depth on the linear
characterization of site effects: Tests on the KiK-net database, Bulletin of Seismological Society of America, submittedin january 2013-b20