An identification procedure of soil profile characteristics

from two free field acclerometer records

Z. Harichanea, H. Afrab,*, S.M. Elachachic

aCivil Engineering Department, University of Chlef, AlgeriabBuilding Research Center, CNERIB, Algiers, Algeria

cCivil Engineering Department, University of Sciences and Technology of Oran, Algeria

Accepted 11 April 2005

Abstract

In this paper, an analytical, numerical and experimental approach for identifying soil profile characteristics by using system identification

and free field records, is presented. First, a theoretical soil amplification function for two sites is defined and expressed in terms of the

different parameters of the layers constituting the soil profiles (thickness, damping ratio, shear wave velocity and unit weight). Then, this

function is smoothed with an analogous function obtained from experimental data by using the least squares minimization technique. The

identification of the parameters is performed by solving, numerically, a non-linear optimisation problem. To demonstrate the numerical

efficiency and the validity of this approach, two examples are treated. The first one consists in the identification of characteristics of a given

uniform soil layer. The second example consists in the experimental validation of this approach with the data recorded within the Garner

Valley Down Hole Array (GVDA). Finally, this approach is applied to identify, simultaneously, soil profile characteristics of sites from only

a single soil acceleration record at free surface of each site. This procedure is utilised to identify soil profile characteristics of sites by using

strong ground motions data recorded during the recent Boumerdes earthquake of May 21, 2003.

q 2005 Elsevier Ltd. All rights reserved.

Keywords: System identification; Soil profile characteristics; Amplification function; Strong ground motion

1. Introduction

It has long been recognized that local site conditions and

local effects are significant factors on earthquake ground

motion on soft soil sites and the need of taking them into

account becomes pronounced when an earthquake strikes a

region [1]. In more recent years, the inclusion of site effects

in code provisions has received a large attention by the

engineering community [2–4].

Local site response may be evaluated by theoretical or

empirical methods. The theoretical methods allow the use of

detailed data on soil layers [5–8]. On the other hand, the

empirical methods are based on seismic records on sites of

different geological conditions which require a large

0267-7261/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.

doi:10.1016/j.soildyn.2005.04.001

* Corresponding author. Address: Building Research Centre, CNERIB,

Cite Nouvelle EL MOKRANI Souidania, Algiers, Algeria.

E-mail address: afra_hamid@yahoo.com (H. Afra).

number of records produced by real earthquakes [9–11]. It

takes a long time to obtain a reasonably complete data set in

regions with low seismicity. Mitigation of earthquake risk in

regions with high seismicity requires detailed microzona-

tion studies, which need the mechanical parameters of the

soil strata. These parameters are obtained usually by in situ

and/or laboratory testing methods [12,13]. In particular,

analyses of down hole seismic array data can provide unique

information on actual and overall site behaviour over a wide

range of loading conditions that are not readily covered by

in situ or laboratory experimental procedures [14]. How-

ever, it is widely recognized in Ref. [11] that there are

significant discrepancies between laboratory results and

attenuations observed in situ. So, since these tests are

generally costly, needing expensive equipment and highly

qualified personnel, the main objective of this study is to

present an analytical, numerical and experimental approach

for identifying characteristics of soil profiles that reduces

significantly the operational cost, by applying system

identification techniques to free field records. System

identification may be performed using two records: one on

Soil Dynamics and Earthquake Engineering 25 (2005) 431–438

www.elsevier.com/locate/soildyn

Z. Harichane et al. / Soil Dynamics and Earthquake Engineering 25 (2005) 431–438432

a free surface and the another on outcropping rock, the case

corresponding to a rock under the soil profile is more rare, or

by using two records on the free surfaces of two sites

without the need of a record on outcropping bed rock or hard

layer.

System identification applied to soil response during

earthquakes has proved a useful tool for estimating in situ

characteristics of soils in previous researches [15–17]. Loh

et al. [18] have estimated the possible effects of the source

(corner frequency, high frequency decay rate of accelera-

tion) as well as the local soil characteristics (depth of soil

deposit, soil density and shear modulus) on the spectral

characteristics of ground motions by developing a stochastic

soil amplification function for a uniform soil layer and using

data recorded by SMART-1 array on Lotung site in Taiwan.

After that, a system identification method was applied to

identify the hysteretic behaviour of soil deposits [19]. Some

other previous studies on system identification carried out at

Lotung site are reviewed in Ref. [20]. In their study, Glaser

and Baise [20] have estimated dynamic properties (shear

stiffness and damping ratios) of the soils at Lotung site from

seismic vertical array measurements (input–output data

sets) using both time-invariant and time-variant parametric

modelling methods (system identification) and modelling

the soil system by a simple lumped mass.

In the present approach, a theoretical soil amplification

function for two sites is defined and expressed in terms of

the different parameters of the layers constituting the soil

profiles (thickness, damping ratio, shear wave velocity and

unit weight). Then, this function is smoothed with respect to

the one obtained from experimental data by using the least

squares minimization technique. The identification of the

parameters is performed by solving, numerically, a non-

linear optimisation problem.

To demonstrate the numerical efficiency and the validity

of this approach, two examples are treated. The first one

consists in the identification of characteristics of a given

uniform soil layer. The second example consists in the

experimental validation of this approach by using the data

recorded within the Garner Valley Down Hole Array

(GVDA) [21].

For more complete and rigorous characterisation of sites

and for more appropriate use in Earthquake Engineering

computations, this approach is applied to identify, simul-

taneously, soil profile characteristics of sites from only a

single soil acceleration record at free surface of each site.

This procedure is utilised to identify soil profile character-

istics of sites by using strong ground motions data recorded

during the recent Boumerdes earthquake of May 21, 2003.

2. Identification method

The present system identification method is based on the

least squares minimization technique described in more

details in Ref. [22] and applied in Ref. [23]. The error

function c2 is minimised according to the parameters vector

{g}, in frequency domain:

c2ðfgg;uÞ Z KXNP

iZ1

ðumax

0jyeiðuÞKydiðfgg;uÞj

2du (1)

where ydi({g},u) is the frequency response of the model and

yei(u) is the measured response on the Np considered points.

umax is the maximum frequency defining the measured

function and K is a normalization factor,

K ZXNP

iZ1

ðumax

0jyeiðuÞj

2du

!K1

:

The local minimum of c2 ({g},u) is obtained under two

conditions: the first one is the nil gradient condition and the

second one is the positive Hessien matrix condition.

3. Simultaneous identification of soil profilecharacteristics of two sites from single record

at the free surface of each site

3.1. Formulation of the equations

Having two records yA(t) et yB(t) at free surface of two

sites A and B (Fig. 1), respectively, their respective

frequency contents YA(u) and YB(u) can be obtained by

using the Fast Fourier Transform [24]. By assuming that the

frequency content is the same at the two bedrocks of sites A

and B, YBR(u)Za YAR(u) where a is a coefficient which can

be determined from the attenuation laws, the soil amplifica-

tion functions corresponding to the two sites A and B are

defined by assuming one dimensional model, by the two

respective equations TA;RðuÞZYAðuÞ=YARðuÞ and TB;RðuÞZYBðuÞ=YBRðuÞ. By considering the ratio between the two

amplification functions, the ‘measured’ function yei(u) can

be defined as:

yeiðuÞ Z aYAðuÞ

YBðuÞ(2)

The soil deposit of each site A and B is assumed to be

linear elastic and horizontally stratified and the distance

between record stations is assumed so long to satisfy the one

dimensional model assumption (Fig. 1). The governing

equation of motion for a vertically propagating shear wave

from bed rock to free surface in each layer of an non-

homogeneous soil deposit is:

v2uj zj;t

� �vt2

Z V2Sj

v2ujðzj;tÞ

vz2(3)

where VSj and zj (0%zj%hj) are, respectively, the shear

wave velocity and the depth in the jth layer of the soil deposit

(Fig. 1). hj is the thickness of the jth layer.

Eq. (3) is a linear partial differential equation of the

second order with constant coefficients. By assuming

Fig. 1. Modelization of soil profiles of two sites under vertically propagating shear waves SH.

Z. Harichane et al. / Soil Dynamics and Earthquake Engineering 25 (2005) 431–438 433

uncoupled modes, the general solution of this equation can

be written as:

ujðzj;tÞ Z UjðzjÞeiut (4)

where Uj(zj) is the mode shape amplitude which can be

written in the form, with pjZu/VSj:

UjðzjÞ Z Ajeipjzj CA0

jeKipjzj (5)

where i is the complex number (i2ZK1) which is different

to index i in the above and below Equations. The constants

Aj and A 0j which are the amplitudes of incident and reflected

waves, respectively, in each layer j (jZ1, N where N is the

number of layers in the soil profile) are obtained from the

boundary conditions: (1) nullity of the shear stress at free

surface, (2) continuity of displacements at the interface

between the j and jC1 layers and (3) continuity of the shear

stress at the interface between the j and jC1 layers. These

conditions lead to:

AjC1 Z1

2Ajð1 CqjÞe

ipjhj C1

2A0

jð1 KqjÞeKipjhj (6a)

A0jC1 Z

1

2Ajð1 KqjÞe

ipjhj C1

2A0

jð1 CqjÞeKipjhj (6b)

with qjZffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiðrjGj=rjC1GjC1Þ

p. The effect of material damping

can be taken into account by introducing complex material

properties in each layer j: V�SjZVSj

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi1C2ixj

pand Gj

*ZGj(1C2xji) where Gj is the shear modulus and xj denotes the

ratio of the linear hysteretic damping of S-waves in the jth

layer [25]. In this way, the ratios pj and qj defined previously

become pjZu=V�Sj and qj ZrjV

�Sj=rjC1V�

SjC1. rj and rjC1 are

the unit weight in the j and jC1 layers, respectively.

By defining, simultaneously, the soil amplification

functions TA,R({gA},u) and TB,R({gB},u) for each site A

and B as the ratio of the amplitude of displacement at free

surface of soil profile to the amplitude of displacement at the

interface between soil and bedrock with the assumption of

one dimensional model (Fig. 1), both take the same form of

the following equation:

T1;NC1ðfgg;uÞ Z2A1

ANC1 CA0NC1

(7)

where A1 and ANC1 are the amplitudes of incident waves at

free surface and at bedrock, respectively, and A 0NC1 is the

amplitude of reflected wave at bedrock. {gA} and {gB} are,

respectively, the parameter vectors of sites A and B.

To clarify the parameter vector {g} in the expression of

the soil amplification function in Eq. (7), we have expressed

the amplitudes Aj and A 0j (jZ3, NC1), respectively,

of incident and reflected waves in terms of the character-

istics (thickness hj, damping ratio xj, shear wave velocity VSj

and unit weight rj) of each layer j of multi layer soil

profile (Fig. 1). For this, we have written the

recurrence relationship between the wave amplitudes in

the j and jK1 layers of the multi layer soil profile that has

leaded to the following forms with the free surface condition

(A1ZA 01):

(a)

if Aj and A 0j are expressed according to the character-

istics of the first layer (iZ1):

Aj

A0j

( )Z

1

2

� �jK1

½H½M11

1

( )A1 (8)

with ½HZQ2

kZjK1½Mk.[M]k is a matrix,

½Mk Z1 Cqk

� �eipkhk 1 Kqk

� �eKipkhk

1 Kqk

� �eipkhk 1 Cqk

� �eKipkhk

" #;

and k is an index (1%k%N).

(b)

If Aj and A 0j are expressed according to the character-

istics of the ith layer (1!i!N):

Aj

A0j

( )Z

1

2

� �jK1

½P½Mi½Q1

1

( )A1 (9)

with ½PZQiC1

kZjK1½Mkand ½QZQ1

kZiK1½Mk.

Z. Harichane et al. / Soil Dynamics and Earthquake Engineering 25 (2005) 431–438434

(c)

If Aj and A 0j are expressed according to the character-

istics of the Nth layer:

Aj

A0j

( )Z

1

2

� �jK1

½MjK1½G1

1

( )A1 (10)

with ½GZQ1

kZjK2½Mk.

So, by distinguishing the different cases treated above, the

soil amplification function for a soil profile overlaying a rigid

bedrock can be expressed in the two following general forms:

(a)

According to the characteristics of the Nth layer:

T1;NC1ðfgg;uÞ Z1

12

� �NVðfgg;uÞ

(11)

where the function V({g}, u) is given by:

Vðfgg;uÞ Z eip1h1 CeKip1h1 (12a)

for a mono layer soil profile, or by:

Vðfgg;uÞ Z eipN hN ðG11 CG12ÞCeKipN hN ðG21 CG22Þ

(12b)

in the case of multi layer soil profile (NO1).

(b)

According to the characteristics of the layer with index i

(1%i!N) of the multi layer soil profile:

T1;NC1ðfgg;uÞ Z2

12

� �NVðfgg;uÞ

(13)

where V({g}, u) is in the form:

Vðfgg;uÞ Z ½ð1 Cq1Þeip1h1 C ð1 Kq1Þe

Kip1h1

!ðH11 CH21ÞC ½ð1 Kq1Þeip1h1

C ð1 Cq1ÞeKip1h1ðH12 CH22Þ (14a)

if it is expressed according to the characteristics of the first

layer (iZ1) or in the form:

Vðfgg;uÞ Z ½ð1 CqiÞeKipihi ðP11 CP21ÞC ð1 KqiÞe

Kipihi

ðP12 CP22ÞðQ11 CQ12ÞC ½ð1 KqiÞeipihiðP11 CP21Þ

C ð1 CqiÞeipihiðP12 CP22ÞðQ21 CQ22Þ (14b)

according to the characteristics of the layer with index i

(1!i!N).

The terms Hij, Pij, Qij and Gij (i, jZ1, 2) are the

components of [H], [P], [Q] and [G] matrixes, defined above,

respectively.

3.2. Definition of the model function and its gradient

The model function ydi({g}, u) in the present case of

simultaneous identification of two soil profiles of two sites,

which can be defined by Eq.

ydiðfgg;uÞ ZTA;RðfgAg;uÞ

TB;RðfgBg;uÞ

is rewritten in the following form:

ydiðfgg;uÞ ZT1;NAC1ðfgg;uÞ

T1;NBC1ðfgBg;uÞ(15)

NA and NB are the layer numbers constituting the soil profiles

of sites A and B, respectively. The parameter vector of the

model is defined as fggZ gAgB

n oand the partial derivatives

of the model function ydi({g}, u) with respect to any model

parameter gj (jZ1, mACmB), where mA and mB are the

number of components in vectors {gA} and {gB}, respect-

ively, are given by:

vydiðfgg;uÞ

vgj

Z1

T1;NBC1ðfgBg;uÞ

vT1;NAC1ðfgAg;uÞ

vgj

KT1;NAC1ðfgAg;uÞ

ðT1;NBC1ðfgBg;uÞÞ2:vT1;NBC1ðfgBg;uÞ

vgj

(16)

In the minimisation algorithm, the partial derivatives are

calculated in two steps:

ð1Þvydiðfgg;uÞ

vgjA

Z1

T1;NBC1ðfgBg;uÞ,

vT1;NAC1ðfgAg;uÞ

vgjA

;

jA Z 1;mA (17a)

ð2Þvydiðfgg;uÞ

vgjB

ZKydiðfgg;uÞ

T1;NBC1ðfgBg;uÞ

vT1;NBC1ðfgBg;uÞ

vgjB

;

jB Z mA;mA CmB (17b)

where vT1;NAC1ðfgAg;uÞ=vgjAand vT1;NBC1ðfgBg;uÞ=vgjB

are

the partial derivatives of amplification functions with respect

to parameters of sites A and B, respectively. In the case of soil

profile overlaying bedrock, the set of model parameters

(vector {g}) is equal to 4NK1 where N is the layers number

of considered soil profile for any site.

4. Validation and applications

4.1. Validation

In order to test the numerical efficiency and the validity of

the present minimisation method, we applied it to the

following two examples.

4.1.1. Identification of characteristics of uniform soil layer

This example consists in identification of characteristics

(thickness h1, damping ratio x1 and shear wave velocity VS1)

of uniform soil layer (Table 1) overlaying a rigid rock

Table 1

Characteristics of uniform soil layer

Parameter Actual Initial estimates Identified

h1(m) 10.0 08.0 08.7

x1(%) 10 15 10

VS1(m/s) 200 190 173

Fig. 4. Accelerations recorded at 22 m depth of Garner Valley site.

Z. Harichane et al. / Soil Dynamics and Earthquake Engineering 25 (2005) 431–438 435

(VS2Z1500 m/s and r2Z2400 kg/m3). In this case, the

identification can be done with respect to the complex form

or with respect to the moduli of the soil amplification function

between free surface and bedrock. To apply this method, it

must get an initial guess for the model parameters. These

estimations as well as the identification results are given in

Table 1. The soil amplification functions corresponding to

actual, initial and identified parameters are compared in

Fig. 2. This figure shows an extremely good agreement

between identified and actual amplification functions but the

identified parameters (h1, x1, VS1) are slightly different to the

actual ones. In other hand, the ratio h1/VS1, initially estimated

to the value 0.042, converges exactly to the actual value 0.05,

about ten iterations.

4.1.2. Experimental validation of the method

This example consists in the validation of the presented

method with experimental data recorded within the Garner

Valley Down Hole Array (GVDA) [21]. The recorded

accelerations at free surface and 22 m depth are plotted in

Figs. 3 and 4. The soil amplification function between free

surface and 22 m depth, computed by mean of spectral ratios

Fig. 2. Amplification function of uniform soil layer.

Fig. 3. Accelerations recorded at free surface of Garner Valley site.

technique is smoothed by a triangular window of 0.5 Hz

width. In Fig. 5, we compare the modulus of smoothed

spectral ratio, the amplification function corresponding to

initial estimates of parameters and the one corresponding to

identified parameters. The minimisation error is about 8%,

for frequencies interval between 0 and 20 Hz.

Fig. 5 shows that the identified amplification function is in

good agreement with the experimental one. The peak

amplitudes are influenced heavily by the damping ratio in

the soil strata. In fact, the damping ratio initially estimated at

3% between 1 and 6 m, 4% between 6 and 9 m and at 1% for

depth greater than 9 m leads to amplification functions for

which the peak amplitudes become flat progressively

according the frequency. The identification algorithm

corrects the values of damping ratio to 2.4% at 8 m depth,

11% at 11.65 m depth and to a value smaller than 0.1%

beyond theses depths. In a previous study on Garner Valley

site, Pecker [21] proposed a possibility to reduce the peak

amplitudes by increasing the damping ratio in the soil strata

which was not retained since it would lead to unrealistically

high values (7–10%), in view of the low input motions and

adopted the possibility of having a rate dependent damping

(xZ0.086f 0.68) for the soil. In return, the corrected values of

damping ratio by mean of the identification algorithm give

peak amplitudes of amplification as well as the corresponding

natural frequencies (error smaller than 2%) closer to the

actual values as illustrated in Table 2.

The identified shear wave velocities are plotted in Fig. 6

versus depth H below the ground surface. The identified

design velocity profile (VS(m/s)ZKH0.28(m), KZ117 for

H%14 m and KZ160 beyond 14 m) with an excellent

Fig. 5. Amplification function between 0 and 22 m of Garner Valley site.

Table 2

Comparison of peak amplitudes of amplification functions and corresponding natural frequencies of Garner Valley site

Frequency’s no Initial estimates Experimental Identified

f (Hz) Peaks Amplitude f (Hz) Peaks amplitude f (Hz) Peaks amplitude

1 3.2959 24.3589 2.7466 8.3251 2.9297 13.4036

2 8.4229 13.9359 8.8501 10.9124 8.7891 14.3918

3 13.4888 9.9006 13.6719 36.0179 13.6719 37.8450

4 18.2495 8.2616 18.0054 11.4693 18.0054 9.2198

Z. Harichane et al. / Soil Dynamics and Earthquake Engineering 25 (2005) 431–438436

coefficient of correlation (0.94) for H%14 m is also presented

in Fig. 6. The identified velocity profile has a similar form to

the Pecker’s [21] design profile (VS(m/s)ZKH0.25(m), KZ135 for H%14 m and KZ150 beyond 14 m) obtained by

matching the data (seismic refraction, SPT, laboratory tests).

Fig. 6 shows that identified velocities are in good correlation

with laboratory and in situ results for depth smaller than

14 m. Beyond this depth, the identified velocities are lightly

scattered with regard to the Pecker’s design profile.

In the identification of the different parameters of the

adopted model and the identification of the corresponding

amplification functions of Garner Valley site, we have used

single recorded component motion at free surface (0 m) and

the corresponding one at rock (22 m). Obviously, compi-

lation of dense recordings leads to better identified results. In

other hand, the identification approach seems to identify well

the ratios h/VS of the different layers of the strata and the

corresponding amplification functions (Fig. 2), nevertheless

its sensibility to the high number of parameters (35

parameters in this example).

Fig. 6. Shear wave velocity profiles of Garner Valley site.

Fig. 7. Accelerations recorded at free surface of site of Hussein Dey city.

4.2. Applications

On May 21, 2003, a 6.8 magnitude earthquake hit northern

Algeria, severely damaging the city of Boumerdes (about

50 km east of Algiers), the capital city of Algiers, and a

number of small cities in Algiers–Boumerdes region [1]. In

order to contribute in understanding earthquake hazard, we

aim, in the applications below, to determine the soil profile

characteristics that should be taken into consideration in

detailed microzonation studies in most of the northern

regions of Algeria, particularly the city of Algiers.

Since the mainshock, several records of strong ground

motions were recorded by the Algerian’s strong motion

instrumentation network that is operated and maintained by

the National Earthquake Engineering Research Centre (CGS)

in and around the epicentral region. Because the E–W

acceleration components were consistently larger than the N–

S components for all recording stations [1], those correspond-

ing to the city of Algiers (Figs. 7–9), are used in the

simultaneous identification of soil profile characteristics

(layer thickness, damping ratio, shear wave velocity and

unit weight) of two sites by minimizing on the modulus

Fig. 8. Accelerations recorded at free surface of site of Dar Elbeida city.

Fig. 9. Accelerations recorded at free surface of site of Kouba city.

Fig. 11. Comparison between the spectral ratio of the sites of Kouba and

Dar Elbeida cities and the corresponding identified amplification function

ratio.

Table 4

Soil profile Characteristics of the site of Dar Elbeida city

Layers

no

Depth

(m)

Layer (m)

Thickness

Damping

Ratio (%)

Shear Wave

Velocity

(m/s)

Unit

Weight

(kg/m3)

1 01.6 1.6 4.9 184 1211

2 06.4 4.8 3.7 291 1182

3 09.6 3.2 2.4 319 1273

4 16.7 7.1 3.4 395 1000

5 – Half-space 0.0 450 1500

Fig. 10. Comparison between the spectral ratio of the sites of Hussein Dey

and Dar Elbeida cities and the corresponding identified amplification

function ratio.

Table 3

Soil profile Characteristics of the site of Hussein Dey city

Layers

no

Depth

(m)

Layer (m)

thickness

Damping

ratio (%)

Shear wave

velocity (m/s)

Unit weight

(kg/m3)

1 01.9 1.9 2.7 261 758

2 05.9 4.0 1.9 306 1129

3 09.1 3.2 1.9 285 989

4 11.8 2.7 2.6 284 1442

5 17.6 5.8 2.2 408 1000

6 – Half-space 0.0 450 500

Z. Harichane et al. / Soil Dynamics and Earthquake Engineering 25 (2005) 431–438 437

of smoothed spectral ratios of three sites two by two

(Figs. 10–12). The results of identification of soil profile

characteristics of three sites are presented in Tables 3–5. The

parameter a is considered equal to the value 1.

5. Conclusion

In the present paper, an approach using system identifi-

cation and free field records, for determining soil profile

characteristics, is presented. A one-dimensional model is

used to develop theoretical soil amplification function for two

sites in terms of the different characteristics (thickness,

damping ratio, shear wave velocity and unit weight) of the

layers constituting the soil profiles. This function is then

smoothed with respect to the one obtained from experimental

Fig. 12. Comparison between the spectral ratio of the sites of Kouba and

Hussein Dey cities and the corresponding identified amplification function

ratio.

data by using the least squares minimization technique in the

frequency domain. The identification of the parameters is

performed by solving, numerically, a non linear optimisation

problem.

The validity of this method is demonstrated by using

experimental data recorded within the Garner Valley Down

Hole Array (GVDA).

The new approach was applied for identifying simul-

taneously soil profile characteristics of sites using only a

single soil acceleration record at the free surface of each site.

This procedure has permitted us to identify soil profile

characteristics of sites using strong ground motions data

recorded during the recent Boumerdes earthquake of May 21,

2003.

This approach offers the capability for more complete and

rigorous characterisation of sites serving as support for

constructions at reduced cost compared with the classical

approach using laboratory and in situ tests, when ground

motion data from previous earthquakes are available. The

results from identification also contribute to a better under-

standing of earthquake hazard.

Table 5

Soil profile Characteristics of the site of Kouba city

Layers

no

Depth

(m)

Layer (m)

thickness

Damping

ratio (%)

Shear wave

velocity

(m/s)

Unit

weight

(kg/m3)

1 01.8 1.8 1.5 222 1050

2 05.0 3.2 6.2 285 1373

3 07.9 2.9 3.9 343 993

4 11.8 3.9 7.4 355 1207

5 18.0 6.2 2.0 407 1000

6 – Half-space 0.0 450 1500

Z. Harichane et al. / Soil Dynamics and Earthquake Engineering 25 (2005) 431–438438

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