thThe 14 World Conference on Earthquake Engineering
October 12-17, 2008, Beijing, China

ON THE H/V SPECTRUM
1, 2

Yutaka Nakamura
1

2

President, System and Data Research, Tokyo, Japan
Visiting Professor, Dept. of Built Environment, Tokyo Institute of Technology, Japan
Email: yutaka@sdr.co.jp

ABSTRACT:The H/V spectral ratio is overviewed from its origin and on the application for practical disaster prevention.
First of all the H/V spectral ratio was found from the strong motion records at various sites in Japan. On the soft
ground, horizontal motion is larger than vertical motion. On the other hand, on the hard ground, both horizontal
and vertical motions are similar to each other both on the maximum value and waveform. First, horizontal tovertical ratio was derived from each maximum value and was compared with the softness of ground and theamplification factor. As a result, horizontal to vertical ratio of maximum value highly corresponds to theseground characteristics. On the next step, the H/V spectral ratio of microtremor measured at anywhere wasconfirmed that it is able to estimate the predominant frequency and the amplification factor for any researchers,
and the result of estimation is stable for the measured time and season. The H/V spectral ratio shows theamplification characteristics by the multiple reflections of the SH wave at least around F0, the predominantfrequency of sedimentary layer, and shows the characteristics confused by the Rayleigh wave around 2F0. In
case of less effect of the Rayleigh wave it is possible to estimate not only preliminary peak but also secondary
peak of amplification characteristics caused by multiple reflections with the H/V spectral ratio.

KEYWORDS:
HVSR, QTS, Microtremor, Strong Motion, Predominant Frequency, Amplification Factor

1. INTRODUCTION
Damages caused by the recent earthquakes are concluded as a direct result of local geological conditions
affecting the ground motion. The best approach for understanding ground conditions is through direct
observation of the seismic ground motion, but such studies are restricted to areas with relatively high seismicity.
Because of these restrictions in other methods, such as only at high seismicity area and the availability of anadequate reference site, non-reference site methods have been applied to the site response studies. Microtremor
is a very convenient tool to estimate the effect of surface geology on seismic motion without other geologicalinformation.
The H/V technique, alias QTS, Quasi-Transfer Spectra, fits very well to this description and it has received great
attention from all over the world with its simplicity together with quick information about dynamic
characteristics of ground and structures. Although several researchers claimed that the theoretical background of
this technique is not clear, there have been many successful experimental studies performed. This method is
attractive since it gives the ease of data collection and it can be applied in areas of low or even no seismicity.
The H/V technique was developed by the author with relating borehole investigations together with the strong
motion records analysis, on the various geological site conditions. It was hypothesized that the verticalcomponent of the ambient noise at the ground surface keeps the characteristics of basement ground, is relatively
influenced by Rayleigh wave on the sediments and can therefore be used to remove both of the source and theRayleigh wave effects from the horizontal components.
It is effective to identify the fundamental resonant frequency of a sedimentary layer, with implied amplification
factors that are more realistic than those obtained from sediment to rock site ratios. It has been shown by manyth

The 14 World Conference on Earthquake Engineering
October 12-17, 2008, Beijing, China
researchers (ex. Ohmachi et. al., 1991; Lermo et. al., 1992; Field and Jacob, 1993, 1995) that how such H/Vratio of noise can be used to identify the fundamental resonant frequency and amplification factor of sediments.
Looking to the examples in the study of Nogoshi and Igarashi (1971) which compared the H/V of Rayleighwave with that of microtremor and concluded that microtremor was mostly composed of Rayleigh wave, someof theoretical studies (Lachet and Bard, 1994; Konno and Ohmachi, 1998; Bard, 1998) suggested that the peakon H/V can be explained with the fundamental mode of Rayleigh waves. If we think that this approach is true,
microtremor should be considered to consist of only Rayleigh wave. On the other hand, if we check theexamples given on Nogoshi and Igarashi (1971) carefully (which will be discussed later), we can clearly see that,at the peak frequency of H/V of Rayleigh wave, the energy of Rayleigh wave is very small, nearly zero.
Rayleigh wave has its maximum energy at near trough frequency of H/V. Because of this, peak of the H/V ofmicrotremor cannot be explained by the energy of Rayleigh wave. As it is explained by Nakamura (1989), theH/V of microtremor at peak frequency range can be explained with vertical incident SH wave.

2. ORIGIN OF THE H/V TECHNIQUE
First of all the H/V spectral ratio was found from the strong motion records at various sites in Japan. On the soft
ground, horizontal motion is larger than vertical motion. On the other hand, on the hard ground, both horizontal
and vertical motions are similar to each other both on the maximum value and waveform.

Strong Motion Observation Site

Atamai
Izumikoshi

Izumikoshi Tunnel
GeologicalAtami / Izumikoshi Ha / Hi

Fresh RockMax. Acc. of Atami (Surface)

Weathered RockAtamai
Izumikoshi

Maximum Acceleration of H Component

NS
EW
UD

Cross-section

Max. Acc. of Izumikoshi (Basement)

Figure 1

Maximum Acceleration of V Component

Atami Ha/Va

Relation of Max. accelerations on surface and basement (Nakamura and Saito, 1983)
8

Miyako (Rock)

7

Seikan Under-Sea Tunnel (Rock)
Observed Amplification Factor

Morioka Substation (Soft Ground)

Pacific Coast of Mexico (Rock)
Hill Zone of Mexico City (Rock)Transition Zone (Soft Ground)Lake Zone (Very Soft Ground)

6
5
4
3
2

Izu Peninsula (Rock)
1

Tokyo (Very Soft Ground)

0

1

2

3

4

H/V of Strong Motion(a) Comparison Site Condition and H/V of PGA

Figure 256●Sites along Shinkansen●

Sites in Mexico City

0
0

1
2
3
4
5
Maximum Acceleretion Ratio H/V ofEarthquake Motion

6(b) Comparison H/V and H/H of PGA

Comparisons between Sites and H/VFirst, horizontal to vertical ratio was derived from each maximum value and was compared with the softness ofground and the amplification factor. As shown in Figures 1 and 2, horizontal to vertical ratio of maximum value
highly corresponds to these ground characteristics (Nakamura et al., 1983).

th(b) A 24-hours Change in H/V Spectral Ratio

Figure 3 Stability of H/V Spectral Ratio

Amlification

Amlification(a) A 24-hours Change in Horizontal Spectrum

Amlification

Amlification

The 14 World Conference on Earthquake Engineering
October 12-17, 2008, Beijing, China

Frequency in Hz

Frequency in Hz

Frequency in Hz

Frequency in Hz

Frequency in Hz

Figure 4 Comparisons between Spectral
Ratios H/V (Rs) and H/H (St) at Mexico
City(a) Comparison H/V of microtremor and Strong Motion

Image of
H/V method(b) Comparison H/V and H/H of Strong Motion

Figure 5 Relation between H/V of Strong
Motion, H/V of Microtremor and H/H of Strong

Figure 6 Image of H/V method

Fo 2Foth

The 14 World Conference on Earthquake Engineering
October 12-17, 2008, Beijing, China
On the next step, the H/V spectral ratio of microtremor measured at anywhere was confirmed that it is able toestimate the predominant frequency and the amplification factor. And as shown in Figure 3 the result of
estimation is stable for the measured time and season (Nakamura, 1989).
From the background of the H/V technique, it is natural that the H/V spectral ratio of not only microtremor but
also the earthquake motion can explain the characteristics, and the original paper (Nakamura, 1989) had pointed
that the H/V spectral ratios of earthquake motion are almost similar to the amplification spectra as shown in
Figure 4. And then as shown in Figure 5, it is confirmed that the H/V spectral ratios of microtremor andearthquake motion are similar to each other and mostly similar to the amplification spectrum (Sato et al., 2004).

3. BASIC STRUCTURE OF THE H/V SPECTRAL RATIO
3.1. H/V Spectral Ratio Technique
There is no reason to enlarge the amplitude of a particular frequency range and of a particular direction at thehard and uniform ground as imaged in Figure 6. It is natural that the vibration of hard ground is uniform foreach frequency range and each direction. The measured results of microtremor and earthquake support it. On
the other hand, under the situation of a soft ground deposition on the hard basement, it is important to grasp the
amplification characteristics of the horizontal motion. At the frequency range amplified the horizontal motion, it
seems vertical motion is not amplified. Meanwhile, at this kind of ground condition, it is important to consider
the Rayleigh wave distributed on the ground surface. Earthquake disaster is caused mainly by the body wave
and if the Rayleigh wave causes any damage, it must be a slight damage. That is to say that it is important tounderstand the phenomenon which the energy of the body wave trapped inside the soft surface layer. The
phenomenon is the amplification of earthquake motion by so called the multiple reflections.
From this view point, the Rayleigh wave plays as a noise and it is necessary to reject the effect of the Rayleighwave. It is possible to understand that the surface layer behaves as a high-pass filter for the Rayleigh wave
propagating in the surface layer as illustrated in Figure 7. Rayleigh wave can not propagate in the frequency
range under the predominant frequency of surface ground (F0), and can transmit the energy peak around thefrequency of minimum group velocity (2F0, Airy phase). So the effect of multiple reflections of the SH wave ismainly composed around F0.

H/V of Rayleigh wave

10

F0

2F0

Figure 7 An Example of Horizontal andVertical Components of Rayleigh wave

Derived from
Results of
Ohta(1963)

1

Impedance
ratio: 1.2 – 4.5
0.1
0.1

1

10

Frequency in unit Cs/4h
Figure 8

H/V of Rayleigh waves for twolayered groundth

The 14 World Conference on Earthquake Engineering
October 12-17, 2008, Beijing, China

Comparison of the vertical motions between the basement and the ground surface makes sure the existence of
the Rayleigh wave. The focused frequency range is around F0, the predominant frequency of the horizontal
motion. The frequency of the vertical motion amplified by the multiple reflections is estimated as Vp/Vs*F0. In
case of the noticed soft ground, while Vs is about 50 m/s to 200 m/s, Vp is around 1000 m/s, near to the Vp ofwater (=1500 m/s). So the frequency that the vertical motion enlarged is 5 to 20 times for F0. Corresponds tothis, the frequency of maximum energy transmission of the Rayleigh wave is approximately 2F0. So it isimportant to judge that the Rayleigh wave effects much if the vertical motion of the ground surface is relatively
larger than the basement at least the frequency range up to three times of F0.
Many peaks are observed on the spectrum of measured microtremor in actual. In past, the analyzers had read thepeak corresponding to the predominant frequency of surface layer based on their experiences and intuitions. It
must be only a speculation because of their arbitrariness. It is necessary for extracting peak for the purpose
exactly to reject the effect of the Rayleigh wave.
The effect of the Rayleigh wave for the surface to the basement ratio of the horizontal motion R (=Ahs /Ahb:
amplification characteristics) is estimated by the surface to the basement ratio of the vertical motion E (=Avs/Avb). Then the corrected amplification characteristic Am is estimated as follows;
Am = R/E= (Ahs /Ahb)/(Avs /Avb)= (Ahs /Avs)/(Ahb /Avb)

(3.1)
(3.2)
(3.3)

Using an observational fact that the ratio Ahb and Avb is nearly equal to 1 for wide frequency range, Am could be
expressed as follows.
Am = Ahs /Avs.

(3.4)

This is the H/V spectral ratio. At present, however, there are many researchers who believe that the peak of the
H/V can be explained by Rayleigh wave. Then the H/V of Rayleigh wave must be discussed.

Relationship between Characteristics ofRayleigh Wave and Impedance Ratio

1

3
Peak and Trough Frequencies of H/V,
Frequency of Minimum Group Velocity
in unit Cs/4h

Group Velocity in unit Cs

3.2. H/V of Rayleigh Wave
For different wave-lengths, Ohta (1963) calculated H/V and phase velocity of Rayleigh waves for two layers
model for various impedance ratio (varying between 1.2 and 4.5) and Poisson’s ratio (varying between 0.25 and

0
1

2

3

Fr eq u en c y i n u n i t C s / 4h
Figure 9 Group velocities of Rayleigh waves

trough frequency of H/Vpeak frequency of H/V
freq. of min. group velocity

2.5
2
1.5
1
0.5
0
0

1

2
3
Impedance Ratio

4

5

Figure 10. Relationship between characteristics ofRayleigh wave and impedance ratio

th

The 14 World Conference on Earthquake Engineering
October 12-17, 2008, Beijing, China
0.49) both in sedimentary and basement layers. By using these calculated results, the relationship between the
H/V of Rayleigh wave and the frequency is shown in Figure 8, and it shows the relations between impedance,
peak and frequency. The frequency in this figure is normalized with the predominant frequency of surface layer,
F0 = Cs/(4h). Group velocities calculated from phase velocities are normalized with S wave velocity and drawn
with the frequency normalized with F0. Figure 9 shows the distribution of group velocity versus frequency. As
we follow this figure, if the impedance ratio is less than two, the energy of Rayleigh wave exists at the lower
frequency range. Figure 10 shows the change of impedance ratio for frequencies of trough and peak of H/V andminimum group velocity of Rayleigh waves. The frequencies corresponding to the trough and minimum groupvelocity (for almost all impedance ratio values), change between 1.5 and 2. On the other hand, only for the peakfrequency varies in a wider range for different impedance ratio. The energy of the Rayleigh wave is almost zeroat the peak frequency of H/V, and at the trough frequency of H/V the energy becomes to maximum. When the
impedance ratio is greater than 2.5, the Rayleigh wave does not affect the H/V peak of ground motion. And on
the other hand, when the impedance ratio is less than 2.5, the Rayleigh wave affects the H/V peak of groundmotion.
3.3. Comparison between Microtremor and Rayleigh Wave for H/V
Figure 11, modified after Nogoshi and Igarashi (1971), shows relationship between H, V and H/V for
microtremor and for Rayleigh wave. It can be clearly seen from these figures that, the energy of Rayleigh wave
does not appear on the peak of H/V of Rayleigh wave. We can easily see that there is no energy around the peakfrequency of H/V and amplitude is almost zero for horizontal and zero for vertical components of Rayleighwaves. On the other hand, the energy of Rayleigh wave gets its maximum on later frequencies at minimumgroup velocity of Rayleigh wave and this is nearly equal to trough frequency which is almost two times of the
H/V peak frequency. The peak of vertical component corresponds to Rayleigh wave, but the peak of horizontal
component is not caused by Rayleigh waves. These figures show that the peak of the H/V is not caused byRayleigh waves.
Figure 8 shows that the H/V of Rayleigh wave for a hard ground, corresponding impedance one, is estimatedaround 0.7, against 1.0 from microtremor measurement on rock sites. It also shows that the H/V spectral ratio of
microtremor around the peak is not caused by the Rayleigh waves.
hvofmtHakodate Eng.

0.5

HV

0.4

h
v

0.3
0.2
0.1
0
0

0 - L ve el o f Am5

lip ut d e

10freq in Hz

15

20

Power spectral
density functions|F(ω )|2 andundergroundstructures of locationsof microtremors
observations sites

0.2

Spectral, vertical andhorizontal responses ofRayleigh waves (M11)0

Hakodate Uni. Naka
h
v

0.1

0

5

10

15

20

Observed andtheoretical ratio of
the horizontal
component (u0) to
the verticalcomponent (w0) of
Rayleigh wave
(M11)

Figure 11. Relation of H, V and H/V for microtremor and for Rayleigh wave (modified
after Nogoshi and Igarashi, 1971)

th

The 14 World Conference on Earthquake Engineering
October 12-17, 2008, Beijing, China
The H/V spectral ratio shows the amplification characteristics by the multiple reflections of the SH wave at least
around F0, and shows the characteristics contaminated by the Rayleigh wave around 2F0. In case of less effect of
the Rayleigh wave it is possible to estimate not only preliminary peak but also secondary peak of amplification
characteristics caused by multiple reflections with the H/V spectral ratio.
3.4. Comparison of the H/V spectral ratio between Earthquake and Rayleigh Wave
Figure 12(a) shows the H/V of strong ground motion of two different earthquakes recorded at the same site.
Although the waveforms show different shape, if we take the H/V, they show similar shape. Another example
can be found also in a paper of Okuma et al. (1999) which is given in Figure 12(b). The results show again thatH/V gives similar characteristics for the different earthquakes recorded at the same sites. If we think that the
H/V of earthquake record can be explained by Rayleigh wave, we should see same characteristics for all
directions of the site, but this is out of practice and it is proper to think that the H/V of earthquake motion
indicate the transfer function of local surface ground, as same as the H/V of microtremor.
NS

H

H/V

V

H/V (QTS) of Strong Motion Acceleration

NS

Freaqency(a) Osaki (Nakamura et. al., 1989)(b) Miyazaki (Okuma et. al. , 1999)

Figure 12. H/V of strong ground motion for different earthquakes recorded at the same station.

3.5. Numerical Simulation for H/V
The H/V indicates the transfer function of local surface ground. This was confirmed from the numericalsimulation performed by Bonnefoy-Claudet et al. (2006) objecting the theory above mentioned contrary to theiropinion. This paper is to consider the characteristics of H/V spectral ratio of microtremor experimentally using
numerical ground model of two layer; basement and surface grounds with 6.5 of the impedance ratio. The firstnatural frequency of surface ground is set to 2Hz. Various shape, location and depth of source are adopted forthis analysis. In case of weak Rayleigh waves the peak corresponding to the second natural frequency 6Hz
appeared. The weaker the Rayleigh waves, the more correct the amplification factor. Consequently, it is natural
to consider that the peak of 2Hz is caused by the multiple reflections of S waves except strong affection of theRayleigh waves near the source. The peak valueat 2Hz varies only between 5 and 8 for 6.5 ofimpedance
ratio.
This
indicatestheamplification factor can be estimated by the
H/V peak value correctly.
3.6. Summery of the H/V Characteristics
Figure 13 shows the typical shape of the H/Vspectral ratio. The characteristic of H/V for
microtremor is summarized as follows. The firstpeak near F0 consists of S-wave mainly. The
first trough near 2F0 is caused by Rayleigh wave.
Around F0 there is almost no energy of Rayleighwaves, so the dispersion curves are unstable

1.0

Effect of the Rayleigh Wave:
Small
Middle
Large

F0

2F0

3F0

Figure 13 Image of the H/V Spectral Ratioth

The 14 World Conference on Earthquake Engineering
October 12-17, 2008, Beijing, China
near F0. Rayleigh wave are growing from F0, and reach the first peak near the 2F0. It is verified that the H/Vspectral ratio of both microtremor and strong motion is useful for estimation of at least fundamental frequency
F0 and its amplification factor. Consequently the excellent papers of Nogoshi and Igarashi (1971) and Suzuki(1933) have no relation to the H/V technique directory.

4. APPLICATIONS TO HAZARD MITIGATION TECHNOLOGY
From above discussions we can now conclude that peak of thespectral ratio H/V is caused by the multiple reflections of S waves.
Alias QTS, Quasi Transfer Spectrum, represents the meaning
coming from its name. Here, it should also be addressed the depthof the basement and the vulnerability of the surface ground relatedwith QTS.
4.1. Basement Depth
The frequency F0 related with QTS is;
F0 = Cs/(4h)(4.1)

And the amplification factor A for this frequency is related withimpedance ratio. If densities for basement and surface layer aresame then,A0 = Cb/Cs(4.2)

And the depth of basement h is,
H = Cb/(4 A0F0)(4.3)

Where, Cb is S wave velocity of basement.
Figure 14 shows the depth of basement along the Shinkansen line
estimated from microtremor for the case of basement velocity (Cb)
is 600m/sec. The estimated results are compared with boring data
and the results showed that, the contact line between alluvium anddiluvium is the basement of QTS.
4.2. Vulnerability Assessment
Figure 14 Comparison between
Earthquake damage of structural members occurs at the time of
Estimated Depth and Measured one
exceeding the limit of the strain caused by deformation, and it(after Nakamura et.al. 1990)
causes the collapse if the stability of the structure lacked.
SensorSensorThen the vulnerability index focused on the strain wasεor γ = K.×
defined (Nakamura, 1997) as imaged in Figure 15. K
Ksg
γi
Kg
values in 10-6/(cm/s2) are defined to estimate the strain in
Kb
PIC
ε
-6
i
Sensor Ad
the unit of 10 at particular parts of the structures, bymultiplying the maximum acceleration at the engineering
basement and the K value.
Surface grounda

These K values are defined for ground and various
structures, as Kg value for ground, Kj value forembankment, Ks value for rigid frame structure and Kb
value for building. As peculiar K value, Kd value for

Cs S-wave
velocity
C b = 600m/s

γ

d: cm

H (m)

Basement groundFigure 15 Image of K values

th

The 14 World Conference on Earthquake Engineering
October 12-17, 2008, Beijing, China
derailment is defined. In this section, Kg is introduced. For other K values, refer the paper of Nakamura (1997).
For ground, shear strain γ of surface ground is noticed. In general, from γ = 1000×10-6 surface ground begins toshow non-linear characteristics and in γ > 10,000×10-6 large deformation and collapse will occur.
Simplifying the shear strain deformation of surface ground as shown in Figure 16, average shear strain γ ofsurface ground can be estimated by following formula.
A g ×δ
γ = Ag×δ/h(4.4)
Where, Ag is amplification factor, h is thickness of surface
layer, and δ is seismic displacement of the basement ground.

Surface GroundhCs , Ag

Putting S-wave velocities of basement and surface ground as
Cb and Cs respectively, proper predominant frequency Fg of
surface ground is approximately expressed as follows.
Fg = Cb/(4Ag×h)(4.5)

Acceleration of basement ground αb is expressed as follows.

Basement Grounda, Cb
Figure 16. Shear deformation of surface ground

αb = (2πFg)2×δ(4.6)

And γ is expressed by Fg, Ag and Cb as follows:γ = (Ag×αb/(2πFg)2)×(4Ag×Fg/Cb)= (Ag2/Fg)×(αb/(π2Cb))(4.7)

If the efficiency of applied seismic force is assumed to be e% of static force, effective γe is expressed as follows.
γe = Kg(e)×αb(4.8)Kg(e) = e×(Ag2/Fg)/(π2Cb)/100(4.9)

The value of Cb is expected to be nearly constant in a broad area and Kg is a proper value for measured point.
Thus Kg can be considered as an index to indicate easiness of deformation of measured points which is expected

Figure 17 Kg values measured after the 1989 Loma Prieta Earthquaketh

The 14 World Conference on Earthquake Engineering
October 12-17, 2008, Beijing, China
useful to detect weak points of the ground. As we can consider Cb = 600 m/s, we obtain 1/(π2Cb) = 1.69×10-6(s/cm). If we put e = 60%, then Kg(e) is expressed as follows.
Kg(e) = Ag2/ Fg(4.10)The effective strain can be estimated by multiplying Kg(e) value with maximum acceleration of basement
ground in Gal (= cm/s2).
Figure 17 shows the distribution of Kg-values obtained in San Francisco Bay Area after the 1989 Loma-Prieta
Earthquake. For Marina district the result along a line from sea coast to hillside is shown. It shows Kg at thesites where grounds deform much are bigger than 20 and Kg at the sites with no damage are very small.
Considering the maximum basement accelerations around the area are estimated as 50Gal based on observations,
Kg = 1000×10-6 separates the areas liquefied or not.

5. CONCLUSION
The H/V spectral ratio, alias QTS, Quasi Transfer Spectrum, is overviewed from its origin to the application forpractical disaster prevention. The H/V spectral ratio was found from the strong motion records at various sites inJapan. On the soft ground, horizontal motion is larger than vertical motion. On the other hand, on the hardground, both horizontal and vertical motions are similar to each other both on the maximum value andwaveform. It is proved in the present paper that the peak of H/V ratio (QTS), either for microtremor of forearthquakes cannot be explained with Rayleigh waves, since Rayleigh wave energy is very small for the peakfrequency but high on the trough of H/V ratio. Author’s explanation in Nakamura (1989) is correct for
explaining this peak with SH waves. The H/V spectral ratio shows the amplification characteristics by themultiple reflections of the SH wave at least around F0, and shows the characteristics contaminated by theRayleigh wave around 2F0. Based on this result, the way to estimate the basement depth and the vulnerability
indices called K values were introduced. K values are simply derived from strains of ground and structures.
It seems to be possible to find the weak points previously with K values because of the high correlation between
the earthquake damage and K values. There are research groups to establish the database on the vulnerability ofstructures. The H/V spectral ratio is already popular on the various research fields. It is happy that K values
contribute to increase the earthquake-resistant capacity of the city with dissemination of the technique forinvestigation of the earthquake-resistant capacity.

REFERENCES
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Ohta, Y. (1963). On the Phase Velocity and Amplitude Distribution of Rayleigh Type Waves in Stratified Double Layer (in case of λ≠µ) (in Japanese with English abstract), Zisin,
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Sato, T., Saita, J., Nakamura, Y. (2004): Evaluation of the Amplification Characteristics of Subsurface using Microtremor and Strong Motion – the Studies at Mexico City, 13thWCEE.
Bonnefoy-Claudet, S., Cornou,C., Bard, P.-Y., Cotton, F., Moczo, P., Kristek, J. and Fah, D. (2006). H/V ratio: a tool for site effects evaluation. Results from 1-D noise
simulations, Geophys. J. Int., 167, 827-837.