Attenuation of P and S Waves in the Javakheti Plateau, Georgia (Sakartvelo)

Abstract

The frequency-dependent parameters of attenuation of P and S waves in one of the most seismically active regions, of the Javakheti plateau, have been estimated using digital data for the first time. We have analyzed and processed hundred and fifty local shallow earthquakes that occurred from 2006 to 2018 and were recorded by five seismic stations. The quality factors for P waves (Qp) and for S waves (Qs) were evaluated by means of the extended coda normalization method. The obtained Qp and Qs are strongly frequency dependent in the frequency range of 1.5 to 24 Hz, and increase with frequency according to the following power laws: QP=17.4±2.3f1.100±0.033 and QS=28.8±3.3f1.048±0.039. The observed Qs/Qp ratio was found to be greater than unity over the entire frequency range, suggesting that scattering may play the main role in the attenuation of body waves on the Javakheti plateau. The frequency dependence of the S wave is very similar to the frequency dependence of the shear wave for another seismically active region of Georgia, the Racha area. A comparison of our results to those other regions of the world shows that among the seismically active areas, the Javakheti plateau is characterized by relatively low values of Qp and Qs, but they are more than volcanic regions such as Etna and Qeshm Island, Iran. The observed results characterize the entire earth’s crust in the study area and will be useful for source parameter estimation, ground motion prediction, and hazard assessment of the Javakheti plateau.

Full text

Research Article
Attenuation of P and S Waves in the Javakheti Plateau,
Georgia (Sakartvelo)
Ia Shengelia, Nato Jorjiashvili , Tea Godoladze, Irakli Gunia, and Dimitri Akubardia
Institute of Earth Sciences and National Seismic Monitoring Centre, Ilia State University, Tbilisi, Georgia
Correspondence should be addressed to Nato Jorjiashvili; nato_jorjiashvili@iliauni.edu.ge
Received 27 June 2022; Revised 30 October 2022; Accepted 5 November 2022; Published 15 November 2022
Academic Editor: Salvatore Gambino
Copyright © 2022 Ia Shengelia 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.
The frequency-dependent parameters of attenuation of P and S waves in one of the most seismically active regions, of the
Javakheti plateau, have been estimated using digital data for the first time. We have analyzed and processed hundred and fifty
local shallow earthquakes that occurred from 2006 to 2018 and were recorded by five seismic stations. The quality factors for P
waves (Qp) and for S waves (Qs) were evaluated by means of the extended coda normalization method. The obtained Qpand
Qsare strongly frequency dependent in the frequency range of 1.5 to 24 Hz, and increase with frequency according to the
following power laws: QP=ð17:4±2:3Þf1:100±0:033 and QS=ð28:8±3:3Þf1:048±0:039. The observed Qs/Qpratio was found to be
greater than unity over the entire frequency range, suggesting that scattering may play the main role in the attenuation of body
waves on the Javakheti plateau. The frequency dependence of the S wave is very similar to the frequency dependence of the
shear wave for another seismically active region of Georgia, the Racha area. A comparison of our results to those other regions
of the world shows that among the seismically active areas, the Javakheti plateau is characterized by relatively low values of Qp
and Qs, but they are more than volcanic regions such as Etna and Qeshm Island, Iran. The observed results characterize the
entire earth’s crust in the study area and will be useful for source parameter estimation, ground motion prediction, and hazard
assessment of the Javakheti plateau.
1. Introduction
The study of numerous tasks of seismology and engineering
seismology is impossible without assessing the properties of
attenuation of seismic waves. Namely, the attenuation proper-
ties of seismic waves are important for studying earthquake
source physics, earth structure, and simulation of strong
ground motion. Especially, the spectral content and attenua-
tion of transverse S waves are essential for engineering seis-
mology as they are the main parameters for seismic hazard
assessment, and 0.8-10 Hz waves are the most interesting for
engineering structures. Therefore, the attenuation of S waves
has been studied more intensively than that of P waves. Gen-
erally, the quality factor Q(inverse of attenuation), which is
the measure of the decay rate of a seismic wave’samplitude
at a narrow frequency range, is used to characterize the atten-
uation of seismic waves. It is a nondimensional parameter and
is determined as the ratio of wave energy to the energy dissi-
pated per cycle of oscillation [1, 2]. When seismic waves travel
through the Earth, their amplitudes decrease and the seismic
waves attenuate. Attenuation of seismic energy depends on
geometric spreading (due to the wave field extension), scatter-
ing (due to different scale heterogeneities randomly distrib-
uted in the lithosphere), and intrinsic absorption (due to the
inelasticity of the medium, mainly by converting seismic
waves’energy into heat). Thus, total attenuation is the sum
of scattering and intrinsic attenuation and provides informa-
tion about the composition and geological structure of the
Earth. Numerous works in the world show that Qvalues can
characterize the seismic activity and geological environment
Hindawi
International Journal of Geophysics
Volume 2022, Article ID 4436598, 10 pages
https://doi.org/10.1155/2022/4436598

of the region. Namely, it is lower in tectonically active areas
and higher in stable regions, e.g. [3].
Since the early 1970s, evaluating attenuation by coda
waves has become a widely used method due to the proper-
ties of coda waves [2–9]. According to Aki and Chouet [2]
coda waves are formed by the superposition of scattering S
waves from heterogeneities of different scales. They intro-
duced the seismic attenuation parameter coda QCand devel-
oped the single backscattering model for QCestimation. The
coda waves at the short distance are caused mainly to single
scattering and the decay rate (envelope) of coda amplitudes
of local earthquakes at distances up to 100 km, in a narrow
frequency range is independent of site effect, hypocentral
distance, and magnitude. Consequently, coda waves charac-
terize the average properties of the medium. Besides coda
waves, the quality factor Qcan also be estimated using body
waves QP, and QS, Lg wave—QLg [2, 10–14]. The attenua-
tion of seismic waves in the Caucasus until the 21st century
was mainly estimated from analog data (their frequency
range is limited). Development of the net of digital seismo-
graphs in Georgia began in 2003 and it becomes possible
to use modern methods in solving various problems of seis-
mology. In recent years, the number of digital records has
increased intensively: and currently, there are 47 seismome-
ters and 6 accelerometers. Seismic hazard assessment is one
of the main tasks in our country and the probabilistic seis-
mic hazard maps need to be updated continuously. Georgian
scientists try to improve studies related to seismic hazards
according to European, American, and Japanese building
codes in order to improve the Georgian because, recently,
the number of construction and various engineering projects
significantly has increased in Georgia including the Javakheti
area, and they need proper seismic design of high standards.
Seismic wave propagation in the earth’s crust and its attenu-
ation is one of the important issues for seismic hazard anal-
ysis. Thus, we need to study it carefully, especially when we
are not spoiled by a similar type of research in Georgia. Since
the postcollision volcanic plateau of the Javakheti is one of
the most hazardous regions of Georgia and is interesting
from both seismic and tectonic points of view, we have esti-
mated the attenuation properties of P and S waves by apply-
ing the extended coda normalization method [11, 15] using
the data of the local earthquakes at different frequencies.
There are various methods to evaluate attenuation parame-
ters of seismic waves, but we chose coda normalization
methods because QCestimates for the Javakheti were made
earlier [16] using the single backscattering model [2] in the
frequency range 1.5-24 Hz and for four lapse time windows
(20, 30, 40, 50 s). Observed QCvalues were low and
increased both with an increase of frequency and lapse time.
QCestimates and their frequency-dependent relationships
were in a range of values of tectonically active and highly
heterogeneous regions. The decrease of coda attenuation
with lapse time was explained due to decreasing homogene-
ities with depth, since the lapse time increased, the coda
waves were generated in larger and deeper volumes of the
earth, which became more homogeneous than the upper
layers of the Earth’s crust.
The Caucasus region is considered to be well-studied
from a geological and geophysical point of view [17]. There
is a sufficient number of articles about the attenuation of
seismic waves (body and surface waves) for the Caucasus
(e.g., [18–21]), but only a few papers in which the attenua-
tion properties of the lithosphere under the Javakheti plateau
have been evaluated, and they were done mainly by means of
analog records [22–24]. As it was noted [25], Georgia was
the first country in the Caucasus where the attenuation
properties of the earth’s crust were investigated using the
coda waves. In the early eighties of the last century, Qpand
Qswere estimated by the coda normalization method on
the basis of analog data for the entire territory of Georgia
(but the attenuation was not estimated for the Javakheti area
separately) in epicentral distances from 50 to 300 km [26].
Though in 1984, coda QCwas estimated in the frequency
range of 0.6 to 42 Hz using the ChISS apparatus, which
was installed in Akhalkalaki and was designed by Zapolskii
[27]. This record was similar to instruments used by Aki
and Chouet [2]. The coda was analyzed in a time window
of 20-120 s. The dependence of QCon frequency was
expressed by the following equation QC=48f0:98. Then QC
values were determined for the Javakheti plateau using only
one digital seismic station AKH and only one coda window
equal to 40 s and established the relationship QC=41f1:052
[24]. Finally, the coda QCwas estimated in different coda
windows using five digital stations [16]. Thus, in particular,
the attenuation properties of the lithosphere under the Java-
kheti plateau have not been previously estimated from digi-
tal data. Therefore, in the future, the estimates of Qpand Qs
will be used to solve various problems of seismology and
engineering seismology in the study area.
2. The Study Region
Georgia belongs to the Mediterranean belt and is located in
the western part of the South Caucasus within the conver-
gent boundary between the Arabian and Eurasian plates,
where the relative motion is mainly carried out by the fold
and thrust belts within the Greater and Lesser Caucasus
[28–31], (Figure 1(a)). Therefore, the active tectonics of
Georgia and the Javakheti plateau (which is located in the
south of Georgia in the central Caucasus) is determined by
the collision of the Arabian and the Eurasian plates in the
Miocene-Pleistocene. The study region—the Javakheti pla-
teau—is a unique region of Georgia due to its geographical
location and geological complexity. Throughout the region,
the Baku-Tbilisi-Ceyhan oil pipeline and the South Caucasus
gas pipeline are passing. Also, highways connecting Georgia
with Turkey and Armenia and other communications of
international importance are being built. Along with natural
disasters typical for mountainous areas—floods, landslides,
erosion of river banks, etc.—the entire territory of the region
is the most seismically active region of Georgia with a max-
imum magnitude of 7.2 and the reoccurrence period of such
events is of order 103–104years [31]. Thus, it is important
to investigate and assess the damage from natural disasters
in this area and to solve those problems knowledge of the
2 International Journal of Geophysics

attenuation of seismic waves versus distance is one of the
main issues.
The Javakheti highland is a young tectonic unit formed
during Neogene–Quaternary era and is a classic example of
continental collision volcanism [32]. The territory is a rather
complex orographic system of high mountain ranges and
deep tectonic troughs. The Javakheti plateau contains several
dozen volcanic centers of the Late Neogene and Eopleisto-
cene, most of which correspond to fault zones [33]. In the
central part of the study area in the meridional direction,
the high mountain ranges Samsari and Kechuti are stretched
(Figure 2) which are part of the biggest stratovolcano of the
Javakheti highland. The high seismicity of this plateau is
caused by the activity of these deep faults. They are the main
source of both weak and large earthquakes. As a rule, volca-
nic environments are highly heterogeneous, the unconsoli-
dated volcanic rock may increase the effect of scattering
[34] and intrinsic attenuation [35], and accordingly, Q
values are relatively low in such regions.
In general, Georgia is characterized by moderate seismic-
ity (Figure 1(b)). The number of earthquakes and the maxi-
mum intensity in Georgia are less than in neighboring
Turkey and Iran, but strong earthquakes have often been
observed in its territory. Javakheti is distinguished by a large
number of small earthquakes from other regions of Georgia,
as well as from the Caucasus. Large earthquakes are located
along the main tectonic faults. The specificity of the seismic-
ity of the region is due to the high degree of fragmentation of
active faults into separate small crustal blocks. Because of the
small blocks of the earth’s crust, they cannot accumulate
large seismic energy, so small earthquakes occur there
almost every day [36]. According to [37], since Javakheti is
an area of young volcanism, a large number of weak earth-
quakes could have a volcanic origin. Large earthquakes also
occurred in this territory. The three largest earthquakes
occurred during the instrumental period: Tabatsquri (1940,
M6), Paravani (1986, M5.9), and Spitak (1988, M7). Three
historical earthquakes (M≥6:5) are also known from
ancient Georgian annals in 1088, 1283, and 1899. Earth-
quakes on the Javakheti plateau are characterized by differ-
ent types of focal mechanisms such as strike-slip, normal,
and thrust The region is experiencing N-S compression
and W-E extension [36]. The GPS data also confirms this
fact [38].
3. Data and Methods
We have analyzed the data of 150 earthquakes recorded by
the National Seismic Monitoring Centre Network of Ilia
State University from 2006 to 2018. Records have been
obtained from five seismic stations AKH, ABS, BGD, BRNG,
and DMN equipped with broadband Guralp CMG40T,
CMG-3ESPC, and Trillium 40 seismometers at a sampling
rate of 100 samples per second were used (Figure 2). All sta-
tions are located on volcanic rock. To evaluate QPand QS
values, we have chosen most of those earthquakes and sta-
tions that were previously used to estimate the quality factor
of coda waves QC[16]. Selected earthquakes have the follow-
ing features: the epicentral distances and focal depths are less
than 65 km and 18 km, respectively. The range of local mag-
nitudes is 1.8-4.4. Figures 3 and 4 show the frequency distri-
bution of earthquakes versus local magnitudes and the
number of earthquake records versus hypocentral distance
used in the study to estimate Qpand Qsat different central
frequencies, respectively. More than 500 seismograms with
a signal-to-noise (S/N) ratio equal to or more than three
were processed to assess the quality factors of body
waves—QPand QS.
The quality factors QPand QSwere estimated with the
help of the coda normalization method (CNM), worked
out by Aki [15] for estimating attenuation by normalizing
the direct S wave amplitude by S coda amplitude. Later this
method, Yoshimoto et al.[11] extended for the P wave, and it
is now possible to measure simultaneously the Qpand Qs
(a)
43°N
42°N
41°N
41°E 42°E 43°E 44°E 45°E 46°E
?1
Faults
2
3
4
5
6
(b)
Figure 1: (a) Tectonic setting of the Caucasus region. N.A.F.: North Anatolian Fault, E.A.F.: East Anatolian Fault, N.E.A.F.: Northeast
Anatolian Fault, B.Z.F.T.B.: Bitlis-Zagros Fold and Thrust Belt, N.T.F.: North Tebriz Fault, and P.S.S.F.: Pambak-Sevan-Sunik Fault. The
fastest velocity vector is the northward movement of the Arabian Plate at 25 mm/yr [31]. (b) Epicenters of earthquakes (ML≥2:0)
occurred in Georgia from 2003 to 2019 (grey circles), the active faults are also shown, 1 refers to the strike-slip, 2 refers to the reverse, 3
refers to the left reverse, 4 refers to the right reverse, 5 refers to the normal fault, and 6 refers to the nappe. The Javakheti plateau is
marked with a red frame.
3International Journal of Geophysics

values. This method relies on the assumption that the energy
of coda waves is uniformly distributed in space and for local
earthquakes, P and S wave radiations have the same spec-
trum ratio in a specific frequency range. In turn, at a small
distance (less than 100 km), coda spectral amplitude waves
change proportionally to S wave spectral amplitudes. There-
fore, the spectral amplitudes of coda, P, and S waves vary
proportionally, and the division of P and S wave amplitudes
by coda amplitudes at a fixed lapse time (greater than twice
the direct S wave travel time) removes the source and site
effects that are common for direct and coda waves. Espe-
cially, CNM can be used when an earthquake occurs in a
hard-to-reach place, for example, in the mountains or in a
water area.
Thus, according to the works [11, 15], the quality factors
of P wave (Qp) and S wave (Qs), using the normalization of P
and S wave spectra amplitudes by the coda wave, can be esti-
mated from the seismogram observed at a different fre-
quency range and at a different hypocentral distance by the
following equations:
ln ASf,r
ðÞ
r
ACf,tC
ðÞ

=−πfr
QSf
ðÞ
VS
+ const f
ðÞ
,ð1Þ
ln APf,r
ðÞ
r
ACf,tC
ðÞ

=−πfr
QPf
ðÞ
VP
+ const f
ðÞ
,ð2Þ
where APðf,rÞ,ASðf,rÞ, and ACðf,tCÞare the direct P and S
wave maximum amplitude and coda wave spectral ampli-
tude at a distance r, respectively; fis the frequency; and tC
is a fixed time from the origin. VPand VSare the average
velocities of Pand Swaves. VP=5:9km/s and VS=3:1
km/s [39]. The geometrical spreading factor for body waves
is taken as r−1. The constant terms denote the scattering
characteristics of the Earth medium of a given region. The
QPand QScan be obtained from the slope of the linear
regression equations (1) and (2) expressing the relationships
between the normalization amplitudes of direct and coda
waves—AP/AC,AS/AC—with hypocentral distance.
To process the data, we used the software Seismic Anal-
ysis Code (SAC) [40]. From each seismogram, a trend and
mean value was removed, the baseline was corrected, and a
cosine taper was applied. Then, seismograms were filtered
by using a Butterworth bandpass filter at five frequency
ranges of 1-3 Hz, 2-4 Hz, 4-8 Hz, 8-16Hz, and 16-32Hz with
central frequencies at 1.5, 3, 6, 12, and 24 Hz. Figure 5 shows
the original and band pass-filtered seismograms of the verti-
cal Z component for the 24/07/2007 earthquake M4.4
recorded at the station AKHA.
For each frequency band, we measured the maximum
peak-to-peak amplitudes of P and S waves in a 5 s time win-
dow starting from the onset of each wave on the vertical Z
and horizontal NS components, respectively. Half the value
of the peak-to-peak amplitude is APðf,rÞand ASðf,rÞ. Dif-
ferences in the maximum amplitude of S waves between
the horizontal components generally do not exceed 6%.
Coda spectral amplitudes ACðf,tCÞwere derived from the
root mean squares of the coda amplitudes of the same com-
ponent of the seismogram. ACðf,tCÞwas estimated for the
time window of 5 s centered at tC=50 s measured from
the earthquake origin time for each central frequency. All
data from various stations were combined in a single plot
since the coda wave amplitude decay rates with time (enve-
lope) for the lithosphere under the Javakheti plateau at a
specific frequency range among the five different stations
used for assessing the attenuation of coda waves are the
same due to properties of coda waves [16]. It is independent
of the hypocentral distance (at least up to 70 km), local mag-
nitude, and the azimuth of the station. We have observed the
same trend for the normalized amplitudes of AP/ACand
AS/ACat different stations. Therefore, it was possible to
combine data from different stations in a single graph and
to evaluate the average values of QPand QSfrom the slope
of Equations (1) and (2) (Figure 6). In 18 cases, it was
impossible to measure the ACat tc=50s, due to high noise,
then we used a master curve obtained from the average
decay rate of coda waves in the different frequency ranges
constrained for the Javakheti region at different frequency
bands using local earthquakes. It should be noted that the
use of the reference curve to estimate ACvalues at a fixed
time does not affect its value, since the envelope of coda
amplitudes is the same in a narrow frequency band for dif-
ferent stations of the studied region [16].
4. Results and Discussion
Quality factors of P and S waves QPand QSwere estimated
for the Javakheti plateau by applying the extended coda nor-
malization method [11] according to Equations (1) and (2)
at five frequency bands. Obtained values of QPand QSesti-
mated from the data of all stations are given in Figure 6.
Mean values of QPand QSshow a strong frequency
dependence character in the frequency range of 1.5-24 Hz.
Namely, they increase with increasing frequency. The
observed QPand QSvalues were fitted to the power-law
function of form QðfÞ=Q0ðfÞnat all central frequencies,
42°N
41°N
43°E 44°E
??
Strike-slip
rust
Normal
Figure 2: Map of epicenters of earthquakes (solid circles) and
seismic stations (triangles) used in the present study. Types of
faults are also shown. 1-Samsari, 2-Kechuti.
4 International Journal of Geophysics

where Q0is the quality factor at 1 Hz and nis the frequency
relation parameter [41]. The frequency-dependent quality
factors for P and S waves are expressed by the power law as:
QP=17:4±2:3
ðÞ
f1:100±0:033,
QS=28:8±3:3
ðÞ
f1:048±0:039
:
ð3Þ
The obtained values of quality factors are low and the
values of frequency relation parameter nare more than
unity. This means that the region is highly heterogeneous
and seismically active. The relatively high values of attenua-
tion (low Q) and of nfrequency exponents correspond to the
seismically active areas in the world [11, 25, 42–45]. We
have found that P waves attenuate slightly more rapidly than
the S waves and the ratio of QSto QPis more than unity
(QS/QP>1) in all frequency bands and varies from 1.4 to
1.6 (Figure 7(a)). According to Aki [46], when a wave prop-
agates in heterogeneous media the conversion of a P wave to
an S wave is larger than the conversion of an S wave to P.
Thus, the attenuation of a P wave is greater than that of an
S wave, and as a result, QPbecomes less than Qs. It was
shown in other works in the world that QS/QP>1 for
regions with complex tectonics [3, 12, 47–49].
1.6
16
14
12
10
8
N
6
4
2
01.8 2 2.2 2.4 2.6 2.8 3 3.2
Mag
3.4 3.6 3.8 4 4.2 4.4 4.6
Figure 3: Frequency distribution of earthquakes versus local magnitudes.
f = 1.5 Hz
30
25
20
15
10
5
02010
Hypocentral distance (km)
4030 50 60 70
N
f = 3 Hz
30
25
20
15
10
5
02010
Hypocentral distance (km)
4030 50 60 70
N
f = 6 Hz
30
25
20
15
10
5
02010
Hypocentral distance (km)
4030 50 60 70
N
f = 24 Hz
30
25
20
15
10
5
02010
Hypocentral distance (km)
4030 50 60 70
N
f = 12 Hz
30
25
20
15
10
5
02010
Hypocentral distance (km)
4030 50 60 70
P
S
N
Figure 4: The number of earthquake records versus hypocentral distance used to estimate Qpand Qsat different central frequencies.
5International Journal of Geophysics

Nonfiltered
Filtered at 1.5 Hz
Filtered at 3 Hz
Filtered at 6 Hz
Filtered at 12 Hz
Filtered at 24 Hz
0 102030405060
Time (sec)
–2
0
2
–10
0
10
–4
0
4
–4
0
4
–2
0
2
–10
0
10
x 10 + 4x 10 + 4x 10 + 4x 10 + 4x 10 + 3x 10 + 4
Amplitude (counts)
OT PSC
Figure 5: Example of original and band pass-filtered seismograms (Z component) for central frequencies at 1.5, 3, 6, 12, and 24 Hz,
respectively, for the local earthquake (2007/07/24) with M4.4 and epicentral distance of 30 km recorded at station AKHA. Arrows
indicate origin time, P, S, and coda waves’arrivals.
9Qp (1.5 Hz) = 26 ± 2
8
7
6
9
Qp (24 Hz) = 565 ± 41
8
7
9
8
7
9Qp (3 Hz) = 63 ± 4
8
7
6
9Qp (6 Hz) = 121 ± 8
8
7
6
In (Ap⁎r/Ac)
In (As⁎r/Ac)
Qp (12 Hz) = 274 ± 15
Qs (1.5 Hz) = 42 ± 3
10 Qs (3 Hz) = 99 ± 6
9
8
7
10
8
6
Qs (6 Hz) = 183 ± 12
11 Qs (24 Hz) = 808 ± 57
10
9
8020
Hypocentral distance, r, km
40 60
020
Hypocentral distance, r, km
40 60
11
10
9
8
11
10
9
8
Qs (12 Hz) = 381 ± 20
Figure 6: Plots of normalized P and S wave amplitudes with hypocentral distance at different frequencies and for all seismic stations. The
regression lines and estimated QPand QSare also shown.
6 International Journal of Geophysics

As it was noted above, the values of QCfor the Javakheti
region were estimated at different lapse times [16]. To com-
pare QSand QCvalues, it is needed that the coda and S
waves sample a comparable volume of the Earth. Therefore,
we have selected QCvalues estimated in the 30 s coda win-
dow and QSvalues for earthquakes with travel times less
than about 15 s recorded at hypocentral distances up to
65 km. Frequency dependence of QCat lapse time 30 sec
was expressed by:
QC=47:6±3:8
ðÞ
f1:034±0:048
:ð4Þ
Thus, the frequency exponents (n) are almost equal for
QCand QS. It means that the attenuation mechanisms for
coda and S waves are similar and the coda waves are com-
posed of S waves [5, 15]. According to Aki and Chouet [2],
coda waves at a lapse time of 30 s sample a spherical volume
with a radius of about vst/2 = 47 km, and because the depth
of the crust under the Javakheti is about 48 km [39], the
obtained values of attenuation are average in the crust. How-
ever, QC>QS. Values of QCand QSvary from 74 to 1334
and from 42 to 808, respectively, within the frequency range
of 1.5-24 Hz. It can be explained by possible predominance
scattering effects beneath the study region, i.e., when the
seismic waves propagate in the medium, more seismic
energy is distributed in the coda waves from the direct body
waves. This should be investigated in the future by separat-
ing the total attenuation into intrinsic and scattering attenu-
ations. Figure 7(b) shows the frequency dependence of the
average values of QS,QP, and QC.
It is interesting to compare our results with those
obtained for another seismically active region of Georgia
such as Racha area (Figure 7(b)), where intense volcanism
occurred until the end of the Bajocian age [50]. This region
is located in the Northwest of Georgia at the joint of the
Greater Caucasus and the Transcaucasian middle massif.
The seismic activity of the Racha sharply increased after
the strong earthquake in 1991 M7. We have found that the
effect of intrinsic attenuation is dominated over scattering
attenuation for this region and is a strong function of fre-
quency. Unfortunately, we can only compare QSvalues,
since QPvalues for the Racha region have not been esti-
mated until now. The QSvalues are also low for Racha, they
increase with increasing frequency and are expressed
according to power-law as ð31 ± 2Þf1:038±0:037 [51]. Thus,
the attenuation parameters are similar for these two regions
of Georgia, QSvalues change at 1-24 Hz frequency band
from 42 to 808 and 46 to 863 for Javakheti and Racha
regions, respectively. Low values of quality factors of direct
Swaves are also reported for the North Caucasus [21].
We compared the QPand QSparameters obtained in this
study with other tectonically and seismically active regions
of the world. It is shown from Figure 8 that among the seis-
mically active areas, the Javakheti plateau is characterized by
low values of QPand QSand the relatively high-frequency
exponent n. Only the QSfor the volcanic area of Etna [52]
and the QPin Qeshm Island, Iran [53], are much lower than
those obtained for the Javakheti plateau. The high values of
QPand QSwere observed for South Korea [47], which is
the most stable region among the considered areas. This fig-
ure shows that Qvalues and the rate of their increase in the
Javakheti area are comparable to other seismically active
regions like the Umbria-Marche, Italy [54]; Bhuj, India
[48]; Kanto, Japan [11]; Kinnaur Himalaya [49]; Cairo,
Egypt [55];and Baoshan, China [56].
As was noted in [51], generally the lithosphere of the
Caucasus is characterized by high attenuation. The Caucasus
belongs to a relatively young tectonic structure and the
attenuation of seismic waves in the lithosphere of the Cauca-
sus is large; and, accordingly, the Qvalues are lower than in
10
Frequency (Hz)
20 300
1.2
1.3
1.4
1.5
Qs/Qp
1.6
1.7
1.8
(a)
103
102
Qc
Q
Qc
Qs
Qp
Qs
101
101
100
Frequency (Hz)
(b)
Figure 7: (a) Qs/Qpratio as a function of frequencies for study region. (b) Mean values of QS,QP, and QCversus the central frequency for
the Javakheti plateau (black lines) and the Racha (red lines) region.
7International Journal of Geophysics

those regions where the age of folding is older. The geologi-
cal age of folding in the Lesser Caucasus, where Javakheti is
located, is younger. In such a tectonic structure, the defor-
mations are complex; the earth’s crust below the study area
consists of numerous faults and cracks; and, therefore, the
attenuation is large [50]. The high attenuation in the study
area can also be caused by low-velocity anomalies of P and
S waves found in the Earth’s crust and upper mantle under
the Javakheti plateau [57]. As a rule, a highly fractured
medium is mainly related to low-velocity regions and,
accordingly, to large attenuation. In addition, a high temper-
ature of up to 750
°
C revealed at the Moho depths beneath
the Lesser Caucasus might cause high attenuation in the
study region [58].
5. Conclusion
In the present study, we estimated QPand Qsvalues in the
frequency range of 1-24 Hz and established their frequency
dependence. It was found that QPand Qsincreased from
26 and 42 at 1.5 Hz to 565 and 808 at 24 Hz, respectively.
We have selected the Javakheti plateau due to seismic activ-
ity reasons because, recently, it is one of the most active
regions in Georgia in terms of seismicity. When we study
seismic hazard in Georgia, ground motion prediction
models are one of the significant stages of the analysis. Thus,
we have paid attention to this stage of the probabilistic seis-
mic hazard analysis. Quality factor analysis plays an impor-
tant role to understand attenuation features of the region at
different frequency bands. Especially, geometrical spreading
varies slightly for different regions in Georgia. Thus, each
seismic active region needs to be analyzed separately as we
did in the study for the Javakheti plateau. We have analyzed
seismic attenuation variations for ground motion studies.
This variation can be due to material properties or physical
states of a medium (such as temperature, stress, and water
consistency). For example, the existence of cracks or seismic
fault zones or seismogenic zones may change the attenuation
properties of the region. However, studying physical proper-
ties was not the scope of our studies. In the near future, we
also plan to study attenuation properties based on the
increased number of records (which will be available due
to the increased number of new seismic stations), compare
them with the study presented in the manuscript, analyze
how it changes at different frequency band, and what is the
reason of it from possible reasons mentioned above.
Data Availability
The detailed data about all earthquakes are collected by a
team of the Institute of Earth Sciences and National Seismic
Monitoring Centre (http://ies.iliauni.edu.ge) under the Ilia
State University and access can be done upon the special
request to the institute. Requests for access to these data
should be done via e-mail: earthscience@iliauni.edu.ge.
Conflicts of Interest
The authors declare that there is no conflict of interest
regarding the publication of this paper.
Acknowledgments
This work was supported by the Shota Rustaveli National
Science Foundation of Georgia (SRNSFG), grant number
#FR-19-3657. We would also like to thank the Scientific
Foundation for the financial support.
11
22
3
3
6
6
7
7
8
8
99
4
4
5
5
10
10
103
102
101
103
102
101
101
100101
100
Frequency (Hz) Frequency (Hz)
Qp
Qs
Figure 8: Comparison of QPand QSvalues for different regions. Line 1: South Eastern Korea [47]; line 2: Baoshan, China [56]; line 3: Cairo,
Egypt [55]; line 4: Kinnaur Himalaya [49]; line 5: Kanto, Japan [11]; line 6: Bhuj, India [48]; line 7: this study; line 8: Umbria-Marche, Italy
[54]; line 9: Etna, Italy [52, 59]; and line 10: Qeshm Island, Iran [53].
8 International Journal of Geophysics

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