Research Article
Geomorphology Characterization of Ica Basin and
Its Influence on the Dynamic Response of Soils for
Urban Seismic Hazards in Ica, Peru
Isabel Bernal , Hernando Tavera, Wilfredo Sulla, Luz Arredondo, and Javier Oyola
Instituto Geof´ısico del Peru´ (IGP), Lima, Peru
Correspondence should be addressed to Isabel Bernal; ybernal@igp.gob.pe
Received 16 June 2017; Accepted 27 November 2017; Published 17 January 2018
Academic Editor: Rudolf A. Treumann
Copyright © 2018 Isabel Bernal et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
We evaluated the influence of the geomorphology of Peru’s Ica Basin on the dynamic response of soils of the city of Ica. We
applied five geophysical methods: spectral ratio (𝐻/𝑉), frequency-wavenumber (𝐹-𝐾), multichannel analysis of surface waves
(MASW), multichannel analysis of microtremor (MAM), and Gravimetric Analysis. Our results indicate that the soils respond
to two frequency ranges: 𝐹0 (0.4–0.8Hz) and 𝐹1 (1.0–3.0Hz).The 𝐹-𝐾, which considers circular arrays, shows two tendencies with
a jump between 1.0 and 2.0Hz. MASW and MAM contribute to frequencies greater than 2.0Hz. The inversion curve indicates the
presence of three layers of 4, 16, and 60m with velocities of 180, 250, and 400m/s.The Bouguer anomalies vary between −17.72 and−24.32mGal and with the spectral analysis we identified two deposits, of 60 m and 150m of thickness. Likewise, the relationship
between the velocities of 400 and 900m/s, with the frequency = 1.5Hz, allows us to determine the thickness for the layers of 60
(slightly alluvial to moderately compact) and 150m (soil-rock interface).These results suggest that the morphology of the Ica Basin
plays an important role in the dynamic behavior of the soils to low frequency.
1. Introduction
Ica Basin (IB) is a depression located in western central
Peru between the Coastal and Western Andean mountains
(Figure 1). In lower basin is located the urban area of Ica city.
The main geodynamic events affecting Ica are earthquakes,
inundations, debris flows, rock falls, and sandy eolic deposit.
Ica has been severely damaged by earthquakes, such as the
quakes in 1942 (7.8Mw) and 1996 (7.6Mw) and most recently
the 8.0Mw Pisco earthquake of 2007. The Pisco earthquake
generated maximum intensities of VII-VIII on the Modified
Mercalli Intensity Scale within a 250 km radio, including the
cities Pisco, Ica, and Chincha. This was one of the largest
earthquake of the last 300 years [1] and showed particular
characteristics such as its duration (120 s) and a complex
rupture process that induced a local tsunami.Themost signif-
icant structural damage was observed in adobe and “quincha”
houses, which resulted in more than 590 fatalities and 320
injuries [2]. The structural damage observed in more than
12 villages around Ica, Lima, and Huancavelica was mainly
associated with local site effects (i.e., soil liquefaction along
the coastline and in weakly consolidated soils), the age of
structures, and landslides on the roads [3]. The study area is
located on thick alluvial deposits composed of pebbles and
small blocks embedded in a silty sand matrix [4]. This soil
type and quality will contribute to generating damage on the
surface when earthquake occurs; therefore, it is necessary to
determine the sedimentary basin’s geometry to better under-
stand its dynamic behavior [5]. Understanding this depends
on the soil and basin’s physical and geomechanical properties
(e.g., stratigraphy, lithology, layer thickness, and basal rock),
because they control propagation velocity of shearwaves (𝑉𝑠).
In this study, we evaluate the influence of the geomor-
phology characterization of the Ica Basin and the dynamic
response of soils for urban seismic hazards in Ica. To
estimate these characteristics, we applied five geophysical
methods: spectral ratio (𝐻/𝑉), frequency-wavenumber (𝐹-𝐾), multichannel analysis of surface waves (MASW), mul-
tichannel analysis of microtremor (MAM), and gravimetric
method. We then used these results to know the seismic and
Hindawi
International Journal of Geophysics
Volume 2018, Article ID 9434251, 12 pages
https://doi.org/10.1155/2018/9434251
2 International Journal of Geophysics
South Panam
ericana Highway
Hig
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LS01-ICLS02-IC
LS03-IC
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0 500 1,000250
Pisco earthquake
15/08/2007
Peru
PACIFIC
OCEAN
ICA
Brazil
Bolivia
Ecuador
Colombia
Chile
ICA
NAZCA
PISCO
CHINCHA
PALPAICA
AYACUCHO
LIMA
HUANCAVELICA
AREQUIPA
PACIFIC
OCEAN Tobas crystal vitrea
Monzonite
Eolian deposit
Alluvial deposit
Gravimetric point
Environmental vibration point
Circular array
Refraction line
South Panamericana Highway
Highway
Bridge
District limit
Topographic curve
Hydrography
Urban area
(8.0 Mw)
A
Geology
Kis-q/tbvk
Ks-li/mz
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Ica river
Parcona
Campo
Ferial
Plaza de
Armas
URB. STA. 
Rosa de Lima
Ica river
Stadium
Huacachina
Lagoon
Dune
(Meters)
N
S
W E
Figure 1: Geological setting of Ica, Peru. Black dots correspond to the locations of environmental vibration record, yellow diamonds
correspond to gravimetricmeasurements, and yellow and green triangles correspond to circular seismic arrays.The LS01–LS03 line represents
the linear seismic array. The A-A󸀠 labels indicate the orientation of the gravimetric profile.
geophysical properties of soils of Ica city and generate a two-
dimensional (2D) model of the Ica Basin.
1.1. Geological Framework. The city of Ica represents 36% of
the total surface of the Ica Department and is located in the
lower part of the Ica River Basin (Figure 1). According to
Gomez et al. [6], the most representative geomorphological
features in the area are the dunes, which are formed by coastal
winds near the shoreline and the plain or alluvial valley the
city sits on.The rocky basement of this region is characterized
by a Precambrian coastal basal complex composed of meta-
morphic rocks and in surface by quaternary deposits. The
soils in this area consist of sands and silty-sands with some
fine contents. From a geotechnical perspective, Ica’s urban
area is characterized by soils with low bearing capacity
(1.0–2.0 kg/cm2), although some areas toward the southwest
and southeast show very low (<1.0 kg/cm2) and medium
(2.0–3.0 kg/cm2) bearing capacities, respectively.
2. Methods
2.1. Description of the Methods. In order to know the influ-
ence of the geomorphology of the Ica Basin on the dynamic
response of soils for urban in Ica, we applied five geophysical
methods: spectral ratio (𝐻/𝑉), frequency-wavenumber (𝐹-𝐾), multichannel analysis of surface waves (MASW), mul-
tichannel analysis of microtremor (MAM), and gravimetric
method.
International Journal of Geophysics 3
2.2. Spectral Ratio (𝐻/𝑉) Method. This method allows cal-
culating the empirical soil transfer function (FTE) from the
spectral ratio of the horizontal and vertical component of an
environmental vibration record (natural noise and/or noise
generated by human activity) considering that the vertical
component is not affected by the sedimentary deposits [7–10].
These spectra allow us to know the dynamic parameters of
the soil such as the fundamental frequency, the dominant
period, and the maximum relative amplifications of the soil.
Nakamura [11] reaffirms that the spectral quotient is a reliable
estimate of the site transfer function for 𝑆 waves, allowing
identification of the fundamental frequency of resonance of
sedimentary deposits [12, 13].
2.3. Frequency-Wavenumber (𝐹-𝐾) Method. This method
allows obtaining the velocity profile of the shear waves
(𝑉𝑠) and thickness of sedimentary deposits. This method
considers that the array of sensors is traversed by a flat-wave
front [14, 15] of known frequency, velocity, and direction of
propagation, given in a two-dimensional space defined by the
wavenumber in the direction of𝐾𝑥,𝐾𝑦 [16], Socco et al. 2010.
Finally, the transformation frequency number of wave fre-
quency 𝐹-𝐾 [14, 17, 18] allows obtaining the dispersion
curve to determine the phase velocity of Rayleigh waves
according to their vibration mode [19, 20]. The fundamental
vibration mode is characterized by attenuation in ampli-
tude as the depth increases and the superior modes (first-
mode, second-mode, etc.) by presenting varying amplitudes
at different depth levels [21–24]. Likewise, the nature of
the higher modes results from the constructive interference
of wave reflection in the Earth’s crust [25–27], Foti et al.
2014.
For 𝐹-𝑘, the most sensitive parameters are associated
with the reliability range of each seismic array (Figure 2(a))
because they depend on distance (𝐷), wavelength (𝜆), and
number of waves (K), where 𝐾min and 𝐾max, given in
a two-dimensional space 𝐾𝑥 and 𝐾𝑦 (Figures 2(b) and
2(c)), define the greatest and least contribution of energy
to propagating waves. In Figure 2(d), the discontinuous
curves sectorize the dispersion curves and delimit the highest
resolution zones for the dispersion curve, identifying low
energy zones (lower frequency values) and aliasing zones
with several energy peaks (greater frequency values). The
first is associated with the boundary imposed by the width
of the central lobe of the array’s response function, while
aliasing is associated with the minimum spacing between
geophones.
For the inversion of the dispersion curve, the neigh-
bourhood algorithm [28] is considered, which makes use
of Voronoi’s cell decomposition of the spatial parameters,
based on an approximation of the “misfit” function, which
is progressively refined during the inversion process. The
misfit is proportional to the error in the adjustment of
the empirical dispersion curve with the theoretical curve
obtained with the proposed velocity profile. This parameter
must tend toward low values. For this approach, more than
500 speed models are generated to consider a misfit less than
0.2. The misfit function is defined by the following equation
[29]:
misfit = √ 𝑛𝐹∑
𝑖=1
(𝑥𝑑𝑖 − 𝑥𝑐𝑖)2𝜎2
𝑖
𝑛𝐹 , (1)
where 𝑥𝑑𝑖 is the velocity of the frequency curve 𝑓𝑖, 𝑥𝑐𝑖 is the
velocity of the calculated curve at the frequency curve 𝑓𝑖,𝜎2
𝑖
is the uncertainty of the frequency sample, and 𝑛𝐹 is the
sample frequency number. Finally, the dispersion curve with
its different modes, through a nonlinear process, is inverted
in order to look for a theoretical profile that fits this experi-
mental dispersion curve.
In order to validate the results, the velocity models (𝑉𝑠)
obtained through this process were inverted to obtain a the-
oretical transfer function (FTT) by applying the Thomson-
Haskell method for horizontal stratified media subject to SH
wave action [20, 30], to finally overlay the FTT with the
empirical transfer function (FTE).
2.4. MASW and MAM Methods. Both methods make it
possible to determine the one-dimensional seismic profile of
waves (𝑉𝑠) by means of surface wave measurement tests,
the resolution of which differs at surface and deep levels,
respectively. Multichannel arrays of sensors located at prede-
termined distances along an axis along the ground surface
are considered. MASW considers waves generated by an
impulsive energy source at predetermined points and MAM
considers the recording of environmental vibrations. From
thesemethods we obtain dispersion curves of Rayleigh waves
(phase velocity of the superficial waves versus frequency) and
their inversion allows us to determine the profile of 𝑆 wave
velocity (𝑉𝑠) [31, 32], Socco et al., 2010.
2.5. Gravimetric Method. This method allows the depth of
the soil-rock interface to be determined from the variation
of gravity acceleration on the ground. The method detects
variations in densities in geological units present in the
subsoil (density > 2 gm/cm3 is associated with rocks and
lower with sediments).
The gravimetric data were corrected by free-air using
regional (Shuttle Radar Topographic Mission, SRTM) and
local elevation models (50 × 50 meters’ resolution grid). The
Oasis Montaj software from Geosoft and an average rock
density of 2.5 g/cm3 [33] were used to correct Bouguer. For
topographic correction, the methodology proposed by Kane
[34] and Nagy [35] is considered, in order to obtain a grid of
topographic correction, which through a sampling operation
assigns the correction value to each gravimetric point. Finally,
the Bouguer anomaly values are triangular interpolated.
In order to estimate the depth of the anomalies, the
spectral analysis method proposed by Spector (1968) and
Grant (1970) is used, which allows the grid of Bouguer’s
anomaly to be transformed into the space domain and the
frequency domain. The values corresponding to each slope
of the spectrum, divided by 4𝜋, allow knowing the average
depth of the center of mass of each anomaly. The first line
slope is associated with the depth of the masses generating
the regional anomaly, the second with the depth of the
intermediate sources, and the third with the more superficial
sources.
4 International Journal of Geophysics
Figure 2: Spatial distribution of the frequency 𝐹1 (𝐹 > 1.0Hz) and examples of spectral ratios obtained in several locations.
3. Data Acquisition
Figure 1 shows the locations of the individual measurement
sites discussed in this study. To apply the 𝐻/𝑉 technique,
we used microtremor data collected from 300 measure-
ment points using a Lennartz LE-3D/5s seismometer and a
CityShark digitizer, with a duration of 15minutes permeasur-
ing point. To select which points to record, we considered the
study area’s geological and geomorphological characteristics,
as well as the distribution of urban areas and accessibility.
To apply the 𝐹-𝐾 method, we used microtremors data
obtain by mean circular arrays of seismometers with 10, 30,
100, and 400m radius, acquiring between approximately 30
minutes and 4 hours of data on each array, depending on its
diameter. We considered the center of the arrays the “Campo
Ferial of Ica.” For these arrays we used 10 Guralp 3-channel
seismometers, each with a 24-bit Reftek digitizer.
The MASW and MAM methods use linear arrays of
geophones (sensors), located at predefined distances along an
axis on the surface. The MASWmethod considers the waves
generated by an impulsive energy source at predefined sites.
In the MAM method, use environmental vibrations. Both
methods allow us to obtain the dispersion curve of the surface
waves (phase velocity versus frequency) and its inversion
allows determining the 𝑆-waves velocity profile (𝑉𝑠) [31, 32],
Socco et al., 2010. For both methods, we used an ES-300
instrument equipped with 24 sensors, with a sensitivity of
4.5Hz. We assembled three arrays 144 and 240m long, in
the center and the boundary of the Ica Basin. On the other
hand, for gravimetric method, we performed 80 gravimetric
International Journal of Geophysics 5
Dispersion curve F-K Dispersion curve F-K
Sl
ow
ne
ss
 (s
/m
)
Frequency (Hz)
0.006
0.004
0.002
Sl
ow
ne
ss
 (s
/m
)
Frequency (Hz)
0.006
0.004
0.002 Sl
ow
ne
ss
 (s
/m
)
Frequency (Hz)
0.006
0.004
0.002
0.006
0.004
0.002
Frequency (Hz)
Sl
ow
ne
ss
 (s
/m
)
Dispersion curves
Average dispersion curves
MASW
Curve 2
Curve 1
Curve
2.2
Curve
2.1
0.5 1 5 10
Frequency (Hz)
0.5 1 5 10
Array 400 m
Array 100 m
Array 100 m Array 400 m
Array 30m
Array 10m
Array 10m Array 30m
0.002
0.004
0.006
Sl
ow
ne
ss
 (s
/m
)
10 1.00.80.6
10 1020 20
8
8 8
6
6 4 6
421
Sl
ow
ne
ss
 (s
/m
)
Frequency (Hz)
0.006
0.004
0.002
Figure 3: Dispersion curves (slowness versus frequency) obtained using the 𝐹-𝐾 method, which considers circular arrays with radii of 10,
30, 100, and 400m. Dashed lines indicate reliability ranges and the bars in the curves are associated with the dispersion of slowness for each
frequency. The right panels show the dispersion curves for different seismic arrays and the solid black line represents the average.
measurements distributed in five parallel lines (SW-NE), sep-
arated by an average distance of 300m (Figure 1).Thedistance
between each measurement is about 200m. For the mea-
surements we used a Lacoste & Romberg gravimeter with an
accuracy of ±0.01mGal. We applied an absolute gravity
correction, using as reference base a point near the Rio
Grande Tunnel (978215.134mGal) south of Ica (Figure 1).The
position of each site (coordinates and ellipsoidal elevation)
used the WGS84 system and was determined using a Nikon
DTM-322 Total Station.
4. Results
The predominant frequency (Fr), shear wave velocity (𝑉𝑠) of
the different soil layers, and the depth of the soil-rock inter-
face are three important parameters in the characterization of
physical and dynamic properties of soils to know the urban
seismic hazards in Ica.
4.1. Predominant Frequency (Fr). The frequency analysis (Fr)
shows that soil of Ica responds in two frequency ranges
(Figure 2), 𝐹0 (𝐹 < 1.0Hz) and 𝐹1 (𝐹 > 1.0Hz), with
amplifications varying from factors of 2 to 6 depending on the
location. For 𝐹0we observed Fr between 0.4 and 0.8Hz, with
relative amplifications up to a factor of 5. For 𝐹1, Frs lower
than 2.0Hz are distributed in the center of the Ica city and
along the “Panamericana Sur” road. Toward the eastern and
western borders of Ica, 𝐹1 showed higher frequencies with
relative amplifications of up to a factor of 6. Likewise, near
“Santa Rosa de Lima Urbanization” (to the north), the Ica
River (to the east), and the Huacachina Lagoon (to the
southwestern), we observe Frs for 𝐹0 of 0.35, 0.40, and 0.48
and 1.8, 2.6, and 3.0 for 𝐹1, respectively. It is evident that
the central part of the basin shows low 𝐹0 and 𝐹1 values,
increasing gradually toward the borders of the basin.
Figure 2 shows four representative spectral ratios curves
labeled (a), (b), (c), and (d). (d), located in the central area,
is characterized by the predominance of 𝐹0 (0.4Hz) over 𝐹1
(2.0Hz). In (c), which is close to the Ica River, 𝐹0 and 𝐹1 are
similar, whereas, in (a) and (b), to the east of the Ica River,
we observe predominant 𝐹1 values between 2.0 and 4.0Hz.
These results show that in Ica’s urban area there are two Fr
ranges, 𝐹0 and 𝐹1. Although 𝐹0 tends to disappear, 𝐹1 shows
higher values as the distance from/to the east from the basin’s
center increases. With these results we can infer that the
dynamic behavior of the soils in Ica changes because the soil-
rock interface presents an irregular geomorphology.
4.2. Shear Wave Velocity (𝑉𝑠)
4.2.1. 1D Profile Using the 𝐹-𝐾 Method. Figure 3 shows the
tendencies of the dispersion curves obtained by different
seismic arrays. The reliability ranges (dashed lines) delimit
the areas of maximum resolution for the dispersion curve.
In this case, for a radius of 10m the frequency range is 10 to
15Hz, for 30m it is 5.0 to 8.0Hz, for 100m it is 2.5 to
4.5Hz, and for 400m it is 0.8 to 1.5Hz. We observe that the
energy between the curves varies strongly between 1 and 2Hz,
6 International Journal of Geophysics
Fundamental mode
(Curve 1)
Sl
ow
ne
ss
 (s
/m
)
Higher mode 1 Higher mode 2
Velocity model (Vs)
Vs (m/s)
(Curve 2.1) (Curve 2.2)
Fundamental mode
(Curve 1)
Higher mode 1
(Curve 2.1) Velocity model (Vs)
Velocity model (Vs)
Velocity model (Vs)
Fundamental mode
Frequency (Hz)
0.006
0.004
0.002
Frequency (Hz) Frequency (Hz)
D
ep
th
 (m
)
0
20
40
60
80
100
D
ep
th
 (m
)
0
20
40
60
80
100
D
ep
th
 (m
)
D
ep
th
 (m
)
0
20
40
60
80
100
0
20
40
60
80
100
8004000
Vs (m/s)
8004000
Vs (m/s)
8004000
8004000
Vs (m/s)
0.006
0.004
0.002S
lo
w
ne
ss
 (s
/m
)
Frequency (Hz) Frequency (Hz)
0.0020
0.0016
0.0012
0.0008
0.006
0.004
0.002
20.80.6 1
Sl
ow
ne
ss
 (s
/m
)
Sl
ow
ne
ss
 (s
/m
)
Frequency (Hz)
Frequency (Hz)
(Curve 1)
Fundamental mode
(Curve 2)
0.8
0.6 M
isfi
t v
al
ue
M
isfi
t v
al
ue
0.3
0.2
20108642
0.1
M
isfi
t v
al
ue
0.3
0.2
0.1
0.8
0.6 M
isfi
t v
al
ue
Test 1
Test 3
Test 2
Test 4
1 40.80.4
Transfer function
10
8
6
4
2
Frequency (Hz)
H
/V
1 40.80.4
Transfer function
H
/V
10
8
6
4
2
Frequency (Hz)
1 40.80.4
Transfer function
10
8
6
4
2
Frequency (Hz)
H
/V
1 40.80.4
Transfer function
H
/V
10
8
6
4
2
Frequency (Hz)
1 5 10
1 5 10 1 5 10
1 5 10 1 5 10
Figure 4: Results for the four tests, from left to right: the inversion of the dispersion curves, the velocity profiles of shear waves (𝑉𝑠), and the
correspondence of the theoretical transfer function (FTT; black line) obtained from the velocity profiles inversion and the empirical transfer
function (FTE; red line) obtained from the spectral ratios for site IC-33.
with a jump that defines two tendencies. The average of the
curves is between 2 and 20Hz, with a moderate deflection
at 8Hz. These tendencies are associated with two frequency
ranges corresponding to different vibration modes of the
Rayleigh waves. Our results show that the velocities forCurve
1 vary between 600 and 2000m/s for frequencies between 0.6
and 1.0Hz, whereas for Curve 2 they vary between 170
and 800m/s for frequencies between 2.0 and 15Hz. Because
of the complexity of the dispersion curve, we conducted
testing to obtain phase velocities combining the fundamental
and higher modes of the dispersion curve, according to
Figure 4. We then inverted the data subsets to reconstruct
International Journal of Geophysics 7
(a)
(b)
(c)
10
2
0
0.2 0.4 0.6 0.81 2 10 20
8
6
4
4 6 8
Frequency (Hz)
Fr
eq
ue
nc
y 
(H
z)
H
/V
-FTT (Inversion LS01-ICA)
-FTE (IC-218)
10
2
0
0.2 0.4 0.6 0.81 2 10 20
8
6
4
4 6 8
Frequency (Hz)
H
/V
-FTT (Inversion LS02-ICA)
-FTE (IC-299)
10
2
0
0.2 0.4 0.6 0.81 2 10 20
8
6
4
4 6 8
Frequency (Hz)
H
/V
-FTT (Inversion LS03-ICA)
-FTE (IC-269)
Velocity profile VsPhase velocity (m/s)
Dispersion curve MASW
Dispersion curve
Amplitude (%)
250
D
ep
th
 (m
)
0
0
0
0 200 400 600 800 1000
2
4
6
8
10
12
14
16
18
Fr
eq
ue
nc
y 
(H
z)
Phase velocity (m/s)
Dispersion curve MAM
0
0
250 500 750 1000 1250 1500
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
20
22
24
26
28
30
0 50 100
−10
−20
−30
−40
−50
−60
−70
−80
−90
−100
LS01-ICA
Resolution rangeResolution range
Dispersion curve
Amplitude (%)
0 50 100
Resolution range
LS02-ICA
LS03-ICA
500 750Vs (m/s)
418000
418000
420000
420000
422000 424000
424000
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South Panam
ericana Highway
Qh-al2
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9-29CI
IC-269
C-218I
0 500250
(Meters)
ACLS02-I
ALS03-IC
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Hig
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o H
uac
ach
ina
422000
Ica river
Huacachina
Lagoon
Dune
Parcona
Plaza de
Armas
Stadium
(f)
(b)
(e)
420
45
0
480
51
0 5
40
42
0
480
420
450
420
42
0
420
420
450
48
0
420
420
420420
420
45
0
42
0
420
420
420
420
42
0
450
45
0
LS01-ICA
1,000
Figure 5: The left panels show the dispersion curves obtained with multichannel analysis of surface waves (MASW; top) and multichannel
analysis of microtremors (MAM; bottom) methods. Here the averages and their inversions allow us to determine the velocity profile. The
central plots show the velocity models (top) for the three linear arrays (bottom).The validation of the results is shown in the plots to the right.
The inversion allowed us to obtain a theoretical transfer function (FTT; black line), which is superposed to the empirical transfer function
(FTE; blue line) and shows a good correlation (degree of correspondence) with the fundamental frequency defined by the vertical gray line.
velocity profiles. We evaluated the effects of frequency range
and combining of mode by comparing the inverted models
obtained from the empirical transfer function (FTE) datasets
(𝐻/𝑉: IC-33) with the theoretical transfer function (FTT)
datasets theoretically obtained from the 𝐹-𝐾method.
The results from four different tests are described thus:
Test 1: Curve 1 corresponds to a fundamental mode of the
Rayleigh waves and Curve 2 is subdivided into the first
and second superior modes of the Rayleigh waves (2.1 and
2.2, resp.). Test 2: Curve 1 corresponds to a fundamental
mode of the Rayleigh waves and Curve 2 corresponds to
a first superior mode. Test 3: Curve 1 corresponds to a
fundamental mode. Test 4: Curve 2 corresponds to a funda-
mental mode. For the first three tests, we obtain velocities
lower than 180m/s at 25m and 300m/s at 38 and 136m,
respectively.These results are not consistent with the geology,
geomorphology, and stratigraphy of the study area; therefore,
we consider these scenarios not representative of the area.
Unlike these tests, Test 4 considers three shallow interfaces
located at 4, 16, and 60m. The first low-velocity layer would
correspond to alluvial material and sandy soils, followed
by the two layers showing velocities of 250 and 400m/s,
composed of moderately consolidated alluvial material to
weakly compacted materials. Here as the depth increases,𝑉𝑠 increases above 900m/s. In this last case, FTT and FTE
coincide with the fundamental frequency of 1.8Hz; thus, this
result is consistent with the areas geology, geomorphology,
and stratigraphy.
4.2.2. 1D Profile Using MASW and MAM. We performed
MASW and MAM surveys on the borders and in the central
part of the basin. The combination of MASW and MAM
techniques allowed us to obtain velocity profiles at depths
up to 60 and 100m. The obtained results are consistent with
a model consisting of three layers (Figure 5); the first with𝑉𝑠 between 170 and 180m/s is composed of loose alluvial
8 International Journal of Geophysics
material (sandy soils); the second with 𝑉𝑠 between 220 and
300m/s is composed of moderately consolidated alluvial
material; and the third with 𝑉𝑠 between 400 and 460m/s is
composed of weakly compacted materials. It is important to
note that as the depth of the layer increases 𝑉𝑠 reaches values
above 600m/s. These 𝑉𝑠 values correspond to layers 40m
thick to the east of the city and 60m thick to the west. At
greater depths, 𝑉𝑠 increases to 800 to 900m/s. In Figure 6
we present the results of the inversion, and we observe that
for the fundamental frequency there is a correspondence
between FTT and FTE represented by the gray line in each
plot.
4.3. Depth of Soil-Rock Interface, Using Gravimetric Analysis.
In Figure 7(a)we show the correctedBouguer anomaly, which
we obtained using the spectral analysis method proposed
by Spector (1968) and Grant (1970). In Figure 7(b), we
identify three gravimetric sources, associated with a residual
or shallow anomaly (sources 1 and 2) and a regional or deeper
(source 3) anomaly. In Figure 7(c), we present the gravimetric
profile including our interpretation. To the west, we observe
that the sedimentary layer is 150m thick, decreasing to 60m
as the topographic elevation increases. These results provide
evidence that the geomorphology of the Ica Basin’s soil-rock
interface is quite irregular because thicker sediment layers are
on the basin’s western border.
5. Discussions
The spectral ratio curves are useful for determining the soil
responses; its resolution is related to the impedance contrast
of the materials, allowing defining different frequencies
and/or frequency ranges at specific sites [36]. In some cases, a
single peak indicates a homogeneous soil, and in other
cases, more peaks are consistent with heterogeneous soils.
However these peaks may not be directly associated with soil
stratigraphy, but rather with nonlinear effects that sometimes
lead to inadequate interpretation [37]. Hence, it is important
to carefully analyze each peak frequency.
The soils in Ica respond to two frequency ranges (𝐹0:
0.4–0.8Hz and 𝐹1: 1.0–3.0Hz). Following the methodology
of Semblat et al. (2002), the maximum relative amplifications
are analyzed in terms of amplitude, frequency, and location
to evaluate their correspondence with geomorphology. In
the central part of Ica, 𝐹0 shows an amplification factor of
four, which decreases rapidly toward the west and gradually
toward the east (Parcona village). 𝐹1 shows amplification
factors between two and three in the sites on the right
margin of the Ica River and amplification factors of five on
the left margin. We observe that these values increase rapidly
toward Parcona village, which is 30m higher with respect to
the elevation of the river. In general, these results show a cor-
respondence of 𝐹0 with regional sources that are modulated
by the Ica Basin’s geomorphology and a correspondence of𝐹1 directly with the stratigraphy of the sediments deposited
on the basin. The results using seismic methods allowed us
to determine that the Ica Basin’s shallow stratigraphic limit
fluctuates between 50 and 60m depth with 𝑉𝑠 between 600
and 900m/s.The gravimetric profiles also show that sediment
thickness is variable along the profile, with layers of ∼150m to
the west and 60m to the east.
To determine the depth of the more representative
interfaces, we applied the relation To = 4𝐻/𝑉𝑠 [38], con-
sidering 𝑉𝑠 values of 400 and 900m/s, with an average
frequency of 1.5Hz. Using these parameters, we found two
interfaces, one at a depth of 66 and one at 150m. The first
interface appears to correlate with moderately consolidated
to slightly compacted alluvial materials, and the second
appears to correlate with the soil-rock interface.These results
agree with those obtained from gravity measurements. On
the other hand, in Figure 7 we show the polynomial fit
used to determine layer thickness, which we then used to
construct the 2D model for the city of Ica. The results
show that the basin consists of an irregular concave surface
with depths of 60 and 150m in the center of Ica, increas-
ing rapidly to the west and decreasing gradually to the
east.
Our results allow us to conclude that 𝐹1 corresponds to
the fundamental frequency of Ica subsoil and 𝐹0 is harmonic
with a regional origin [20] modulated by the Ica Basin.
Finally, the frequency variations at depth that are associated
with the physical characteristics of the soil, local topography,
and geomorphology (dunes, small hills, and plateaus) allow
us to characterize and infer the geometry and alluvial con-
tents of Ica.The depth and irregularities of the basin generate
seismic waves associated with resonance effects within layers
of heterogeneous composition.
6. Conclusions
In this study we determined that the soils in the city of
Ica respond to two frequency ranges: 𝐹0 (0.4–0.8Hz) and𝐹1 (1.0–3.0Hz). 𝐹0 is associated with a regional source
modulated by basin geomorphology and𝐹1 is associatedwith
a local source that corresponds to the dynamic response of the
sediment layer.
Gravimetric and seismic analysis results show that the
depth of the rock-soil interface under Ica varies from 150m
to the west to 60m to the east. The 2D model suggests
that the Ica Basin’s geomorphology consists of a concave
structure with depths that range from 120 to 150m in the
center and decrease rapidly to the west and gradually to the
east.
The correlation of the results obtained using the seismic,
geophysical, and geotechnical methods suggests that the Ica
Basin’s irregular geomorphology plays an important role
in the dynamic response of Ica’s soils to low frequencies,
which produces a variation in the frequencies and rela-
tive amplification in soils despite a relatively flat surface
topography. The structural damage associated with the 2007
Pisco earthquake was larger in the west, which can be
explained by the thicker layer there and the variable dynamic
behavior.
Conflicts of Interest
The authors declare that they have no conflicts of interest.
International Journal of Geophysics 9
South Panam
ericana Highway
Qh-al2
Qh-e
418000
418000
420000
420000
422000
422000
424000
424000
84
42
00
0
84
44
00
0
84
46
00
0
84
48
00
0
0 500 1,000250
(Meters)
Hi
gh
wa
y t
o P
arc
on
a
Hig
hw
ay t
o H
uac
ach
ina
Bouguer anomaly
−17.72
−24.32
(mGal)
84
42
00
0
84
44
00
0
84
46
00
0
84
48
00
0
Ica river
Dune
Plaza de
Armas
Parcona
Huacachina
Lagoon
420
45
0
48
0
51
0 5
40
42
0
480
420
450
420
42
0
420
420
450
48
0
42
0
420
420420
420
45
0
42
0
420
420
420
420
420
450
45
0
Stadium
Bouguer anomaly
map
(a)
Depth =
Depth (km)
slope
Slope
4
(km)
Power spectrum
7.06.02.01.0
0.484
0.141
0.1051.3217
1.7697
6.083Source 1
Source 2
Source 3
0.0 4.03.0 5.0
Wavenumber (1/km)
−10.0
−8.0
−6.0
−4.0
−2.0
0.0
2.0
4.0
6.0
8.0
ＦＨ
(Ｊ
Ｉ
Ｑ
？Ｌ
)
y = −6.083x + 6.1908
y = −1.6862x + 0.5883
y = −1.3217x − 1.2148
(b)
440.0
430.0
420.0
0.1
−0.1
−18.0
−20.0
−22.0
−24.0
000.0
0.00
D
ep
th
 (m
ts)
Bo
ug
ue
r (
m
G
al
)
Re
sid
ua
l
El
ev
at
io
n 
(m
ts)
Stadium Plaza de Ica RiverArmas
1.00 2.00 3.00
Distance (km)
4.00
100.0
200.0
300.0
400.0
0.0
A ！
Residual anomaly
Observed
Calculated
Error 0.031
Quaternary, 1.7gr/cm3
Quaternary, 2.0 gr/cm3
Rock, 2.5 gr/cm3
Rock, 2.7 gr/cm3
(m
G
al
)
(c)
Figure 6: (a) Bouguer gravity anomaly map; (b) spectral analysis derived from the Bouguer gravity anomaly; and (c) gravimetric profile A-A󸀠
(see Figure 1) showing sedimentary deposits and the rocky basement.
10 International Journal of Geophysics
South Panam
ericana Highway
Hi
gh
wa
y t
o P
arc
on
a
Hig
hw
ay t
o H
uac
ach
ina
0 500250
(Meters)
40 meters
155 meters
Thickness
418000 420000 422000 424000
418000 420000 422000
84
42
00
0
84
42
00
0
84
44
00
0
84
44
00
0
84
46
00
0
84
46
00
0
84
48
00
0
84
48
00
0
424000
Ica river
Huacachina
Lagoon
Dune
Parcona
Plaza de
Armas
Stadium
420
45
0
48
0
51
0
54
0
42
0
480
420
450
420
42
0
420
420
450
48
0
42
0
420
420420
420
45
0
42
0
420
420
420
420
420
450
45
0
1,000
(a)
Rock
surface
Surface of
Topographic surface
Thickness (m)
the soil
layer
！
N
E
！
−30
−40
−50
−60
−70
−80
−90
−100
−110
−120
−130
−140
−150
(b)
000.0
0.00
D
ep
th
 (m
ts)
1.00
Seismic line
Surface soil layer, H/V
Rock surface, H/V
Geomorphology of the
Sediments
Rock
LS
2.00 3.00
Distance (km)
4.00
100.0
200.0
300.0
400.0
Stadium Plaza de Ica River
LS01LS02LS03
ArmasA ！
Vs < 500 m/s
Vs < 750 m/s
Ica Basin
(c)
Figure 7: (a) Contour depth map derived from the predominant frequencies; (b) 3D schema of the Ica Basin; and (c) cross section of the Ica
Basin (A-A󸀠), superposed on the results obtained using seismic and gravimetric methods.
International Journal of Geophysics 11
Acknowledgments
This research was supported by Geophysical Institute of Peru
(IGP). The authors would like to thank Betrand Guillier and
Marc Wathelet of the “Institut de Recherche pour le Devel-
oppement (IRD),” for training on the use of tool of Geopsy
and their valuable contributions to the manuscript. Also
thanks are due to Hugo Perfettini (IRD) for the support,
advice, and contribution to their professional life.
References
[1] H. Tavera and I. Bernal, “The pisco (Peru) earthquake of 15
August 2007,” Seismological Research Letters, vol. 79, no. 4, pp.
510–515, 2008.
[2] INDECI, Reporte del sismo del, Instituto Nacional de Defensa
Civil, 2007.
[3] H. Tavera, I. Bernal, F. Stresser, M. Arango-Gavina, J. Alarcon,
and J. Bommer, “Ground Motions observed during the 15
August 2007 Pisco, Peru, event,” Bulletin of Earthquake Eingi-
neering, 2008.
[4] W. Leo´n and V. Torres, “Mapa geolo´gico actualizado del
cuadra´ngulo de Ica (29 - i),” INGEMMET, DGR, 2001.
[5] S. Bonnefoy-Claudet, S. Baize, L. F. Bonilla et al., “Site effect
evaluation in the basin of Santiago de Chile using ambient noise
measurements,” Geophysical Journal International, vol. 176, no.
3, pp. 925–937, 2009.
[6] J. C.Gomez, S.Ortiz, andC.Chiroque, Informe te´cnico, Geologı´a
y geotecnia de la ciudad de Ica, 2013.
[7] K. Kanai and T. Tanaka, “Onmicrotremors. VIII,” Bulletin of the
Earthquake Research Institute Tokyo University, vol. 39, pp. 97–
114, 1961.
[8] M. Nogoshi and T. Igarashi, “On the amplitude characteristics
of microtremor (part 2),” Journal of the Seismological Society of
Japan, vol. 24, pp. 26–40, 1971.
[9] Y. Nakamura, “Method for dynamic characteristics estimation
of subsurface using microtremor on the ground surface,”
Quarterly Report of RTRI (Railway Technical Research Institute)
(Japan), vol. 30, no. 1, pp. 25–33, 1989.
[10] H. Okada, “The microtremors survey method, Geophysical
Monograph Series 12,” Society of Exploration Geophysics of
Japan, p. 155, 2004.
[11] Y. Nakamura, “Clear Identification of Fundamental Idea of
Nakamura’s Technique and its applications in the hill zone of
Me´xico City,” Bulletin of the Seismological Society of America,
vol. 82, pp. 24–43, 2000.
[12] J. Lermo and F. J. Chavez-Garc´ıa, “Site effect evaluation using
spectral ratios with only one station,” Bulletin of the Seismologi-
cal Society of America, vol. 83, pp. 1574–1594, 1993.
[13] F. Leyton, S. Sepulveda, M. Astroza et al., “Zonificacio´n s´ısmica
de la cuenca de Santiago,” in Congreso Chileno de Sismologı´a e
Ingenier´ıa Antis𝜑smica, X Jornadas, pp. 22–27, Chile, 2010.
[14] R. Lacoss, E. Kelly, andM. Tokso¨z, “Estimation of seismic noise
structure using arrays,”Geophysics, vol. 34, no. 1, pp. 21–38, 1969.
[15] T. Kvaerna and F. Ringdahl, “Stability of various fk estimation
techniques, Norsar semiannual technical summary,” Tech. Rep.,
1, –86, 1986.
[16] S. Foti, R. Lancellota, L. V. Socco, and L. Sambuelli, “Application
of FK analysis of surface waves for geotechnical characteriza-
tion,” in Proceedings of the Proc. 4th International Conference
on Recent Advances in Geotechnical Earthquake Engineering and
Soil Dynamics, Paper No. 1.14, San Diego, California, 2001.
[17] K. Tokimatsu, Y. Miyadera, and S. Kuwayama, “Determination
of Shear Wave Velocity Structures from Spectrum Analyses of
Short-Period Microtremors,” in Proceedings of the 10th World
Conf. on Earthquake Eng, vol. 1, pp. 253–258, 1992.
[18] D. J. Zywicki, Advanced Signal Processing Methods Applied to
Engineering Analysis of Seismic Surface Waves, 1999.
[19] K. Aki and P. G. Richards, Quantitative Seismology, University
Science Books, 2002.
[20] K. Aki and P. Richards, Quantitative Seismology: Theory and
Methods, New York, 1980.
[21] M. Wathelet, Array recordings of ambient vibrations: surface-
wave inversion, Lie`ge University, Belgium, 2005a.
[22] M. Wathelet, Geopsy geophysical signal database for noise array
processing, Software, LGIT, Grenoble, France, 2005b.
[23] M. Wathelet, “An improved neighborhood algorithm: Param-
eter conditions and dynamic scaling,” Geophysical Research
Letters, vol. 35, no. 9, Article ID L09301, 2008.
[24] D. Fa¨h, G. Stamm, and H. Havenith, “Analysis of three-
component ambient vibration array measurements,” Geophys-
ical Journal International, vol. 172, pp. 199–213, 2008.
[25] K. Aki, “Space and time spectra of stationary stochastic waves,
with special reference to microtremors,” Bull, Earthquake Res.
Inst. Tokyo Univ, vol. 35, pp. 415–456 (1 plate), 1957.
[26] J. Xia, R. D. Miller, and C. B. Park, “Estimation of near-surface
shear-wave velocity by inversion of Rayleighwaves,”Geophysics,
vol. 64, no. 3, pp. 691–700, 1999.
[27] S. Foti, L. Sambuelli, L. V. Socco, and C. Strobbia, “Experiments
of joint acquisition of seismic refraction and surface wave data,”
Near Surface Geophysics, vol. 1, pp. 119–129, 2003.
[28] M. Wathelet, D. Jongmans, M. Ohrnberger, and S. Bonnefoy-
Claudet, “Array performance for ambient vibrations on a
shallow structure and consequences over vs inversion,” Journal
of Seismology, vol. 12, pp. 1–19, 2008.
[29] M. Wathelet, D. Jongmans, and M. Ohrnberger, “Surface-wave
inversion using a direct search algorithm and its application to
ambient vibrationmeasurements,”Near Surf Geophys, vol. 2, pp.
211–221, 2004.
[30] F. J. Sa´nchez-Sesma, V. J. Palencia, and F. Luzo´n, “Estimation of
local site effects during earthquakes: an overview,” ISET Journal
of Earthquake Technology, vol. 39, no. 3, pp. 167–193, 2002.
[31] C. B. Park, R. D. Miller, and J. Xia, “Multichannel analysis of
surface waves,” Geophysics, vol. 64, no. 3, pp. 800–808, 1999.
[32] C. B. Park and R. D. Miller, “Roadside passive multichannel
analysis of surface waves (MASW),” Journal of Environmental
& Engineering Geophysics, vol. 13, no. 1, pp. 1–11, 2008.
[33] W. Hinze, “New standards for reducing gravity data, The North
American gravity database,”Geophysics, vol. 70, no. 4, pp. 25–32,
2005.
[34] M. F. Kane, “A Comprehensive System of Terrain Corrections
Using a Digital Computer,” Geophysics, vol. 27, no. 4, pp. 455–
462, 1962.
[35] D. Nagy, “The gravitational attraction of a right rectangular
prism,” Geophysics, vol. 31, no. 2, pp. 362–371, 1966.
[36] M. Pilz, S. Parolai, M. Picozzi et al., “Shear wave velocity model
of the Santiago de Chile basin derived from ambient noise mea-
surements: A comparison of proxies for seismic site conditions
and amplification,” Geophysical Journal International, vol. 182,
no. 1, pp. 355–367, 2010.
12 International Journal of Geophysics
[37] C. Cornou, P. Gue´guen, P.-Y. Bard, and E. Haghshenas, “Ambi-
ent noise energy bursts observation and modeling: Trapping of
harmonic structure-soil induced-waves in a topmost sedimen-
tary layer,” Journal of Seismology, vol. 8, no. 4, pp. 507–524, 2004.
[38] SESAME-Project EVG1-CT-2000-00026, “Deliverable D19.06,”
2009,http://sesame-fp5.obs.ujf-grenoble.fr/Deliverables/Del-D19-
Wp06.pdf.
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