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ASSESSMENT OF SEISMIC GROUND CONDITIONS OF THE CITY OF OLMALIQ
Xusomiddinov A.S., Aktamov B.U., Yodgorov Sh.I.,
Yadigarov E.M., Avazov Sh.B., Bozorov J.Sh.,
Teshaeva R.B., Jumaev D.D., Mansurov A.F., Xayriddinov B.B.
Institute of Seismology named after G.A.Mavlonov,
Academy of Sciences of the Republic of Uzbekistan , Tashkent, Uzbekistan
E-mail:
Abstract:
The article discusses the results of field research conducted on the territory of Olmaliq
for engineering and seismological justification of the master plan for the development of the city.
Geophysical and engineering-geological surveys were carried out to assess the influence of soil
conditions on seismic intensity parameters. Calculated values of peak ground accelerations on a
free surface were obtained using the STRATA program. Based on a generalization of field and
laboratory engineering-geological data, sections and a map of the engineering-geological zoning
of the city of Olmaliq were compiled.
Keywords:
engineering-geological conditions, Strata program, KMPV, MASW, soil conditions
models, soil reaction spectrum.
Аннотация:
В статье рассматриваются результаты полевых исследований, проводимых на
территории Алмалыка, для инженерно-сейсмологических обоснований генерального
плана развития города. Геофизические и инженерно- геологические изыскание
проводились для оценены влияния грунтовых условий на параметры сейсмической
интенсивности. Получены расчетные значения пиковых ускорений на свободном
поверхности с использованием программы «STRATA». На основании обобщения полевых
и лабораторных инженерно-геологических данных составлены разрезы и карта
инженерно-геологического районирования города Алмалыка.
Ключевые слова:
инженерно-геологические условие, программа Strata, КМПВ, MASW,
модели грунтовых условий, спектр реакции грунтов.
Introduction.
In the city of Olmaliq, within the framework of the Decree of the President
of the Republic of Uzbekistan dated May 30, 2022 UP -144 "On measures to further improve the
seismic safety system of the Republic of Uzbekistan" and the Resolution of the President of the
Republic of Uzbekistan dated May 16, 2023 PP -158 "On additional measures to further improve
the seismic safety system of the population and territory of the Republic of Uzbekistan", many
seismic observations were carried out. For this purpose, engineering-geological and
seismological surveys are carried out to determine the engineering-geological conditions of the
city's territory. The territory of Olmaliq has some specific features. Loess soils, sandy loams,
sandstones, pebbles are widespread, in which seismic waves propagate differently, have different
speeds of passage, different frequencies, accelerations, etc. Therefore, it is very important to
intensify scientific research in the field of the influence of soil conditions on the seismicity of
construction sites.
The main concept defining the features of engineering and seismological surveys is the
model of seismic ground conditions. This concept includes all local features of the geological
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environment that determine the specifics of seismic impacts, their amplitudes and spectral
composition [1-7].
Research methodology.
A method for modeling seismic soil conditions for assessing the
seismicity of construction sites is proposed, in which real engineering-geological and
geophysical indicators of soils are studied, and the influence of soil conditions on the parameters
of seismic vibrations under real impacts of strong earthquakes is determined. [5;7-15].
To solve the problems of assessing the seismicity of the territory, the STRATA program
was used, taking into account engineering and geological conditions. Actual accelerograms of
two earthquakes were taken, which by their mechanism (normal and reverse) and by the nature
of the propagation of seismic waves correspond to the seismological conditions of the territory of
the Republic of Uzbekistan.
Next, materials were collected characterizing the engineering-geological and seismic
properties of soils (based on archival materials and the results of complex geophysical studies
conducted using seismic exploration methods KMPV (Correlation method of refracted waves),
MASW (Multichannel Analysis of Surface Waves), and the physical and mechanical properties
of the soil layer for 30 meters were also studied), which are widespread in the territory of the city
of Olmaliq. Calculations of the seismic intensity increment were made based on the totality of
seismic soil rigidities, the position of the groundwater level and the resonant properties of the
soils.
The algorithm of actions for solving problems related to the development of seismic soil
models is divided into 3 stages. (Fig. 1)
Stage 1. Collection and systematization of materials.
2nd stage. Data analysis and processing of materials using various programs.
Stage 3. Generalization of results.
Fig.1 - Algorithm of actions for developing seismic soil models
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Analysis.
A loose layer of loess and loess-like deposits is present over most of the study
area. However, its thickness varies significantly. It ranges from 20 m and more within the high
terraces and decreases to 0.5 m on the I and II floodplain terraces of the Ohangaron River
[13;16-18].
In general, the study area shows certainty in the location of areas with different
thicknesses of loess rocks: the areas have an elongated shape and are located approximately
parallel to the modern bed of the Ohangaron River. Moreover, if in areas adjacent to the river the
thickness of loose rocks is small (0-0.5 m), then as you move away from it it increases, reaching
20 m or more. Loess rocks reach their greatest thickness of up to 20 m or more. These deposits
compose the IV terrace of the Ohangaron River.
According to their genesis, these are proluvial-deluvial loess deposits of Tashkent age.
These areas are located in the southern, southwestern and southeastern parts of the territory
under consideration. The area of loess rocks with a thickness of 10-20 m occupies a limited area
in the southeast of the territory and represents the preserved surface of the IV floodplain terrace
of the Ohangaron River [19].
To the north there is a strip of loess deposits with a thickness of 5-10 m, it is located in
the central and eastern parts of the study area and occupies a significant part of the modern
development of the city. The western part of the modern development of the city is located on
loess with a thickness of 2-5 m. These deposits are also noted in the valleys of the side tributaries,
as well as in the north-eastern part of the territory, where they are located in a relatively narrow
strip with a width from several tens of meters to 700-800 m. Loess deposits with a thickness of
0.5-2 m mainly occupy the western part of the area under consideration [4; 12; 20]. This section
also extends in a narrow strip in the direction of the Ohangaron River bed, crossing the city from
west to east (Fig. 2 ).
Fig.2 Engineering-geological section of the city of Olmaliq
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Result.
Seismic exploration using the KMPV (Correlation method of refracted waves)
and MASW (Multichannel Analysis of Surface Waves) methods was performed along five
sections. It is aimed at studying the velocity characteristics of lithological soil types that form the
foundation of the Olmaliq city territory. As a result of processing the seismic exploration data,
the Vs (z) dependencies and depth-velocity models were obtained along profile 1 (Fig. 3) and
profile 2 (Fig. 4). The Vs values are presented in Table 1.
Fig. 3. Depth-velocity model of transverse waves according to MASW. Profile 1
shear wave velocity model ин MASW. Profile 1. ( tab. 1 )
Fig. 4. Depth-velocity model of transverse waves according to MASW . Profile 2
Velocity model of transverse waves according to MASW. Profile 2. ( tab. 1 )
Table 1.
Results of recording the values of transverse wave velocity by depth
Profile 1
Profile 2
Depth, m
Vs , m/s
Depth, m
Vs , m/s
-0 .9
253.33
-0, 92
293.43
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- 2.1
300.10
- 2 ,2 4
463.04
- 3.7
421.69
- 3.60
750.13
- 4.9
544.89
- 5.26
806.36
- 8.1
469.26
-9.20
431.67
- 10.5
397.01
- 13.00
456.78
- 16.7
654.40
- 16.10
925.24
- 17.9
1067.18
- 17.60
1358.48
- 20.6
1439.73
- 22.50
1397.64
-3 0.9
1592.93
-32.3
1156.93
Based on the obtained depth-velocity models, the parameter Vs30 ( Table 2) was
calculated, equal to the average value of the propagation velocity of transverse waves in a 30-
meter thickness.
Table 2 .
Vs30 for each observation point
No.
Profile 1
Profile 2
Vs30, m/s
657.831
683.0419
Below are the samples of the H/V spectrum of registration points 1-11. The following
results were obtained from processing the summary data on the seismic intensity increment using
various methods: ( Table 3)
Table 3 .
No.
Vs30, m/s
ρ30,
g/sm3
HVSR
dI
HVSR dI Final
calculation
1
610.1
1.9
4.7
-0.02
0.44
7.79
2
652.5
1.9
2.82
-0.07
0.45
7.74
3
649.8
1.9
3.5
-0.07
0.41
7.74
4
609.5
1.9
4.1
-0.01
0.30
7.80
5
610.1
1.9
4.4
-0.02
0.45
7.79
6
612.6
1.9
4
-0.02
0.51
7.79
7
656.3
1.9
2.9
-0.07
0.46
7.74
8
655.5
1.9
4.8
-0.08
0.33
7.73
9
609,0
1.9
5.1
-0.02
0.54
7.79
10
645.1
1.9
4.05
-0.06
0.44
7.75
11
502.3
1.8
3.6
0.15
0.29
7.96
13
485.2
1.9
3.6
0.17
0.48
7.98
14
477.9
1.9
3.62
0.18
0.47
7.99
15
416,0
1.8
2.85
0.32
0.51
8.13
16
345.5
1.7
6.3
0.48
0.46
8.29
17
461.6
1.8
3.62
0.21
0.33
8.02
18
662.3
1.9
5.8
-0.08
0.33
7.73
19
466.2
1.9
4.3
0.20
0.52
8.01
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20
376.5
1.7
3.7
0.40
0.56
8.21
21
589.4
1.9
4.7
0.02
0.62
7.83
22
374.9
1.8
3.6
0.40
0.56
8.21
23
532.1
1.9
3.9
0.09
0.38
7.90
24
601,5
1.9
3.8
-0.01
0.44
7.80
25
593.2
1.9
3.9
0.01
0.45
7.82
26
419.7
1.8
3.4
0.29
0.41
8,10
27
469.7
1.9
4.2
0.19
0.30
8.00
28
589.8
2.0
4.4
0,00
0.45
7.81
29
601,0
2.0
-0.02
0.51
7.79
30
498.7
1.9
3.3
0,00
0.46
7.81
31
561.1
1.8
4.6
0.17
0.33
7.98
32
679.3
1.9
4.5
0.06
0.54
7.87
33
550.3
2.0
4.6
-0.14
0.44
7.67
34
622.2
1.8
2.4
0.09
0.29
7.90
35
611.3
1.9
2.8
-0.02
0.48
7.79
36
658.4
1.9
4
-0.01
0.47
7.80
37
634.8
1.9
5.1
-0.08
0.51
7.73
From the peak acceleration profiles, the peak acceleration value on the day surface is
from 0.25g to 0.36g, respectively, for the presented points. The isolines of various peak
accelerations were displayed using the triangle method [21-22] . Based on the equivalent linear
approach, seismic soil models were developed in the STRATA program at 37 observation points
(Fig. 5-6). Having modeled three earthquakes for all 37 points, a seismic zoning map of the
Olmaliq city territory was constructed using the calculation method based on the peak
acceleration values with an initial seismicity of 0.209g ( Table 4 ).
Table 4.
Model of seismic ground conditions for 1 point of the city of Olmaliq
Soil type Depth Soil
power
Shear
wave
speed,
m/s
Soil
density
vs30
m/s
PGA,
(g)
Initial
seismicity
( g)
Seismicity
of the site
(Score)
sandy
loam
0.00
0.60
175.12
1.57
466.2
0.328
0.21
8
sandy
loam
0.60
0.78
193.54
1.59
sand
1.38
1.25
230.62
1.61
sand
2.62
1.18
332.05
1.68
sand
3.80
2.59
492.76
1.84
clay
rocks
6.40
2.59
443.17
1.79
clay
rocks
8.99
3.73
268.52
1.64
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clay
rocks
12.72 2.23
380.56
1.74
gravel-
pebbles
14.95 6.11
738.30
1.94
gravel-
pebbles
21.06 48.94
1014.6
0
2.02
bedrock
70.00 ∞
1200
2.2
Fig. 5. Peak acceleration graph for point 1 of the city of Olmaliq
Fig. 6. Graph of the soil reaction spectrum for 1 point of Olmaliq city
Conclusions.
Based on the conducted research, the following conclusions can be made
about the features of the engineering and seismological conditions of the territory of the city of
Olmaliq: the territory of the city of Olmaliq and the adjacent area are divided into two zones:
- with an increment of seismic intensity of 0 points relative to the reference/benchmark
seismic station (7 points for a 95% probability of not exceeding within 50 years);
- with an increment of seismic intensity of +1 (8 points for a 95% probability of not
exceeding within 50 years);
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In the study area, the following limit values were identified for the maximum acceleration
of soil oscillations: from 0.25 g and 0.36 g .
In the compiled map of seismic microzoning of the territory of the city of Olmaliq on a
scale of 1:25 000, only zone 8 is highlighted.
This article is a practical project presented by the Innovation Development Agency
#ALM-202311142839 “Creation of a digital simulation model of the city of Tashkent allowing
to assess the level of economic damage when exposed to strong earthquakes”, #AL5822012294
“Development of technology for forecasting the risk of strong earthquakes”, #Al-5822012298
“QMQ-normative document 2.01.03.96 “construction in seismic areas” creation of an electronic
database on seismic indicators of soils to change the schedule 1.1 of the seismological part”.
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