Download Effect of Shear Wave Velocity on the Ground Motion Parameters of

Earthquake Ｒesearch in China
Volume 28，Number 2，2014
Effect of Shear Wave Velocity on
the Ground Motion Parameters of
Site Surface1
Cao Junfeng，Feng Weidong，Meng Fanyue，and Dong Shuanglin
Earthquake Administration of Anhui Province，Hefei 230031 ，China
Based on the data from typical sites in the Jianghuai region，many kinds of soil layer
seismic response are modeled by increasing and decreasing the measured values of shear
velocity to a certain scale． The seismic response of soil layer sites are calculated using the
one-dimensional equivalent linear method in the frequency domain by choosing the Taft，
Kobe and El-centro records as the ground motion input． The results show that the impact
of shear velocity variability on the surface ground motion is in relation to the soil layer
structure and ground motion input parameters such as amplitude and spectral
characteristic． With the increase of shear velocity，the PGA ( peak ground acceleration)
on the surface of site will increase，however，the characteristic period of the acceleration
response spectra is decreasing．
Key words: Shear velocity; Peak ground acceleration; Characteristic period
INTＲODUCTION
Because shear velocity can mirror the dynamic characteristics of soil， it has been an
important index for evaluating the site conditions and an indispensable basic parameter of seismic
response of soil layers in evaluation of seismic safety for engineering sites． At present，shear
velocity of soil layers is obtained by an in-situ test，methods mainly including single hole layer
detection method，cross hole method，transient surface wave method and the stable surface wave
method． Due to the difference of drill site selection， construction methods， test method，
instrument precision and artificial operation，the shear velocity test results have a large dispersion
( sometimes up to 30% ～ 40% or more) in the in-situ test，which can bring serious interference
in determining the site ground motion parameters ( Gao Yufeng et al． ，2001; Liu Hongshuai et
al． ，2005; Lan Jingyan et al． ，2006; Chen Guoxing et al． ，2007; Sun Ｒui et al． ，2009 ) ．
Therefore，it is of great significance to study the effect of shear velocity variation of soil layers on
1
Ｒeceived on March 20，2013． This project was sponsored by the Anhui Natural Science Foundation Project
(10040606Q24)，and the Youth Seismic Ｒesearch Program of Anhui Province，China (20120707) and (20140301)．
Earthquake Ｒesearch in China
234
the ground motion parameters， as well as the corresponding influencing range and variation
trends．
Based on the data from typical sites in the Jianghuai region， and by increasing and
decreasing the measured values of shear velocities according to certain proportions and the
influence of shear velocity variations on the peak ground acceleration，the characteristic period
and response spectrum is analyzed． This work can provide reference for rational determination of
seismic fortification criteria for major construction projects in Anhui and other areas．
1
1. 1
ANALYSIS METHOD AND CALCULATION PAＲAMETEＲS
Analysis M ethod
At present，there are many methods for calculating seismic response of soil sites，such as the
linear elastic wave ( and vibration ) analysis method， equivalent linearization wave motion
method，and the direct time-domain nonlinear integral analysis method． The one-dimensional
frequency-domain equivalent linearization wave method， which is also the national standard
“Evaluation of Seismic Safety for Engineering Sites ( GB17741-2005 ) ” recommended approach
( Liao Zhenpeng et al． ，1989) ，is widely used in engineering． This method uses an equivalent
shear modulus and damping ratio to replace all the shear modulus and damping ratio under
different strain amplitudes，thus，converting the nonlinear problem into a linear problem． This
method is used in this study．
1. 2
Basic Calculation Profile
Based on the data from a typical site in the Jianghuai region，using the one-dimensional
frequency-domain equivalent linearization wave method，we choose two typical drillings ZK4 and
ZK24 as the basic calculation profiles． The overburden thickness of the first typical drilling ZK4 is
42. 3m，and ZK4  s covering soil layer is mainly composed of fill soil，clay，coarse sand and
sandstone，which belongs to medium-hard soil． The overburden thickness of the second typical
drilling ZK24 is 29. 4m，and ZK24 s covering soil layer is mainly composed of fill soil，silty clay
and silt mass in silty clay，coarse sand，gravel and sandstone，which belongs to medium-soft soil．
The measured shear velocity and soil layers information of the basic calculation sections are shown
in Fig． 1． Nonlinear dynamic parameters of typical soil samples are obtained from the dynamic
triaxial test，and some of the soil dynamic parameters are derived from classic recommended
values ( Yuan Xiaoming et al． ，2000) ．
1. 3
The Input Bedrock G round M otion
According to the principle for selecting input ground motion，we choose the Taft，Kobe and
El-centro strong motion records as the bedrock input ground motions ( Fig． 2) and the duration of
those records is taken as 40s． The mean peak accelerations of strong motion records are adjusted
to be 50gal，100gal，200gal and 400gal，and any time history with the amplitude damped to onehalf of its value is chosen as the bedrock input ground motions．
2
THE ＲESULTS OF SOIL LAYEＲ SEISMIC ＲESPONSE ANALYSIS
Based on the information of typical drilling ZK4，ZK24，nine soil layer response analysis
models are established by increasing or decreasing the measured shear velocity by 5% ，10% ，
15% ，20% ，respectively on the same profile． Combined with the three input ground motion
records，seismic response of the soil layer sites is analyzed under 216 working conditions． The
Volume 28，Number 2
235
Fig． 1
The drilling histogram of basic profiles
PGA ( peak ground acceleration) and T g ( characteristic period of response spectrum) are shown
in Table 1 ～ Table 2 ( where，A max and T g are the mean of the calculation results using the three
input records with same peak strong motion) ，and T g ( s) is obtained from the abscissa periodic
value at the right intersection point of the response spectrum platform value A max β m with the
response spectrum curve． According to the teaching material of the “Seismic Ground Motion
Parameters Zonation Map of China”( Hu Yuxian，et al． ，2001) ，the amplification factor of the
response spectrum ( β m ) takes 2. 5．
Fig． 3 and Fig． 4 show the ground acceleration response spectrum of the two drillings under
different shear wave velocities of soil layers with E1centro ( NS direction) ground motion as the
input． It can be seen from the figures that:
(1) For first typical drilling ZK4，when the input bedrock PGA is less than 100 gal，ground
acceleration response spectrum in 0 ～ 1. 0s showed slight variations under different shear wave
velocities in soil layers． The shorter the cycle，the more significant changes of response spectrum．
The effect of response spectrum larger than 1. 0s from the shear velocity of soil layers can be
ignored． When the input bedrock PGA exceeds 200gal ( i． e． under violent earthquake ) ，the
shape of the ground surface acceleration response spectrum within 0 ～ 6. 0s is affected to various
extents by shear wave velocities of soil layers， and when shear wave velocity of soil layers
decreases，the long period part of response spectrum moves to the right，the short period spectrum
value decreases，and the long period spectrum increases in general． When shear wave velocity of
soil layers increases，the short period spectrum value increases，the medium and short cycle part
Earthquake Ｒesearch in China
236
Fig． 2
The three input strong motion records
of the response spectrum has a greater effect，and the response spectrum curve moves to the left．
(2) The second typical drilling profile ZK24 contains silt soft soil layer，which shows strong
nonlinearity，thus the input bedrock peak seismic motion has a very limited effect on the ground
acceleration response spectrum． When the input bedrock peak is 50gal，the ground acceleration
response spectrum differs greatly in the period range of 0 ～ 6. 0s． With the increase of the input
bedrock peak，the shape of the response spectrum shows a larger difference，and its overall
performance is consistent with the same tendency of ZK4 under a violent earthquake．
Table 1
Basic
profile
ZK4
ZK24
The peak acceleration A max ( gal) under different shear wave velocities of soil layers
Input PGA
( gal )
－ 20%
－ 15%
－ 10%
－ 5%
Measured
value
+ 5%
+ 10%
+ 15%
+ 20%
50
75. 4
75. 4
78. 6
80. 2
81. 3
83. 5
81. 5
82. 2
83. 3
100
141. 2
144. 3
152. 2
152. 2
155. 5
159. 6
156. 5
157. 4
159. 8
200
283. 9
275. 5
270. 9
287. 4
296. 3
303. 6
295. 8
305. 4
306. 9
400
472. 1
534. 3
594. 5
603. 5
566. 6
547. 6
555. 7
591. 4
608. 2
50
89. 1
84. 9
81. 3
82. 9
87. 5
89. 7
92. 0
98. 7
102. 3
100
145. 7
164. 0
172. 1
171. 2
160. 5
157. 1
160. 6
160. 8
171. 5
200
165. 6
190. 3
214. 8
236. 6
253. 0
279. 0
304. 6
315. 5
307. 8
400
336. 7
355. 9
388. 6
423. 7
453. 0
475. 7
502. 7
524. 1
521. 0
Volume 28，Number 2
237
Table 2
The characteristic period of response spectrum T g ( s ) under different shear wave
velocities of soil layers
Basic
profile
ZK4
ZK24
Input
PGA ( gal )
－ 20%
－ 15%
－ 10%
－ 5%
Measured
value
+ 5%
+ 10%
+ 15%
+ 20%
50
0. 71
0. 69
0. 67
0. 65
0. 63
0. 62
0. 62
0. 60
0. 58
100
0. 72
0. 70
0. 67
0. 65
0. 64
0. 63
0. 62
0. 61
0. 59
200
0. 79
0. 77
0. 74
0. 70
0. 69
0. 67
0. 66
0. 62
0. 61
400
1. 02
0. 97
0. 87
0. 83
0. 80
0. 76
0. 74
0. 72
0. 67
50
0. 82
0. 80
0. 79
0. 75
0. 72
0. 69
0. 67
0. 61
0. 55
100
0. 98
0. 92
0. 86
0. 82
0. 79
0. 76
0. 74
0. 72
0. 68
200
1. 12
1. 05
1. 03
1. 01
0. 97
0. 93
0. 87
0. 83
0. 81
400
1. 17
1. 11
1. 06
1. 02
1. 01
1. 00
0. 99
0. 98
0. 97
Fig． 3
The response spectrum under different shear wave velocities of
soil layers for basic profile ZK4
3 ANALYSIS ON THE EFFECT OF VAＲIABILITY OF SHEAＲ WAVE VELOCITY
OF SOIL LAYEＲS
In order to analyze the influence of shear wave velocity variation of soil layers on ground
238
Earthquake Ｒesearch in China
Fig． 4
The response spectrum under different shear wave
velocities of soil layers for basic profile ZK24
motion parameters，the results of the adjusted shear wave velocity and measured shear wave
velocity are compared and analyzed． In order to show the intuitive deviation，calculation results of
measured shear wave velocity are taken as the reference，and the relative deviation of calculation
results between adjusted and measured shear wave velocity are shown in Table 3，Table 4，Fig． 5
and Fig． 6．
We can see from those results that:
( 1) In the same basic profile，if the measured shear wave velocity of soil layers increases or
decreases by a range of 20% ，the results have a large difference between adjusted and measured
shear wave velocity． The larger the difference in shear wave velocities，the greater the variations
in peak ground acceleration and characteristic period of response spectrum． For the basic profile
ZK4，the variation amplitude of peak ground acceleration is － 16. 7% ～ 7. 3% ，and the variation
amplitude of response spectrum characteristic period is － 16. 7% ～ 27. 5% ; and for the basic
profile ZK24，the variation amplitude of peak ground acceleration is － 34. 5% ～ 24. 7% ，and the
variation amplitude of the response spectrum characteristic period is － 16. 8% ～ 23. 6% ．
(2) The peak ground acceleration is in positive correlation with the shear wave velocity of
soil layers． When the shear wave velocity of soil layers decreases，the peak ground acceleration
also decreases gradually; and when the shear wave velocity of soil layers increases，the peak
ground acceleration also increases gradually． For example，for the basic profile ZK24 under the
Volume 28，Number 2
239
condition of the bedrock input peak being 200 gal，when the soil layer shear wave velocity
decreases by 5% to 20% in succession，the variance of peak ground acceleration also decreases
from － 6. 5% to － 34. 5% ，compared with the results calculated from the measured shear wave
velocity and vice versa．
Table 3
Basic
profile
ZK4
ZK24
Table 4
Basic
profile
ZK4
ZK24
The comparison results of peak ground accelerations
Variances in shear wave velocity ( relative to the measured values)
Input
PGA( gal )
－ 20%
－ 15%
－ 10%
+ 5%
+ 10%
+ 15%
+ 20%
50
－ 7. 2%
－ 7. 3%
－ 3. 3% － 1. 3%
2. 7%
0. 2%
1. 1%
2. 4%
100
－ 9. 2%
－ 7. 2%
－ 2. 1% － 2. 1%
2. 7%
0. 6%
1. 2%
2. 7%
－ 8. 6% － 3. 0%
2. 5%
－ 0. 2%
3. 1%
3. 6%
6. 5% － 3. 4%
－ 1. 9%
4. 4%
7. 3%
5. 1%
12. 8%
16. 9%
200
－ 4. 2%
－ 7. 0%
400
－ 16. 7%
－ 5. 7%
50
1. 9%
－ 3. 0%
－ 9. 2%
2. 2%
100
4. 9%
－ 5%
－ 7. 1% － 5. 2%
7. 2%
2. 5%
6. 6% － 2. 1%
0. 0%
0. 2%
6. 9%
200
－ 34. 5% － 24. 8% － 15. 1% － 6. 5% 10. 3%
20. 4%
24. 7%
21. 7%
400
－ 25. 7% － 21. 4% － 14. 2% － 6. 5%
11. 0%
15. 7%
15. 0%
5. 0%
The comparison results of characteristic period of response spectrum
Variances in shear wave velocity ( relative to the measured values)
Input
PGA( gal )
－ 20%
－ 15%
－ 10%
－ 5%
+ 5%
+ 10%
+ 15%
+ 20%
50
12. 2%
10. 1%
6. 3%
3. 7%
－ 2. 1%
－ 2. 1%
－ 4. 8%
－ 7. 4%
100
12. 0%
8. 9%
4. 2%
2. 1%
－ 1. 0%
－ 2. 6%
－ 5. 2%
－ 7. 3%
200
14. 5%
11. 1%
7. 2%
1. 0%
－ 3. 4%
－ 3. 9%
－ 10. 1%
－ 11. 6%
400
27. 5%
20. 8%
8. 3%
3. 3%
－ 4. 6%
－ 7. 5%
－ 10. 4%
－ 16. 7%
50
13. 9%
11. 1%
10. 2%
3. 7%
－ 3. 7%
－ 6. 5%
－ 15. 7%
－ 23. 1%
100
23. 6%
16. 0%
8. 4%
3. 4%
－ 3. 4%
－ 5. 9%
－ 8. 4%
－ 13. 5%
200
15. 1%
8. 2%
6. 5%
3. 8%
－ 3. 8%
－ 10. 7%
－ 14. 8%
－ 16. 8%
400
15. 5%
9. 6%
4. 6%
1. 0%
－ 0. 7%
－ 2. 0%
－ 3. 3%
－ 4. 3%
(3) The characteristic period of response spectrum is in negative correlation with the shear
wave velocity of soil layers． When the shear wave velocity of soil layers decreases， the
characteristic period of response spectrum will increase; and when the shear wave velocity of soil
layers increases， the characteristic period of response spectrum decreases accordingly． For
example，for basic profile ZK4，under the condition of bedrock input peak of 100 gal，when the
soil shear wave velocity decreases by 5% to 20% in succession，the variance of characteristic
period of response spectrum also increases gradually from 2. 1% to 12% ，compared with the
calculated results of measured shear wave velocity，and vice versa．
(4) In contrast，the effect of decrease of shear wave velocity of soil layers is slightly larger
than its increase on the peak ground acceleration and the characteristic period of response
spectrum．
( 5) The impact of the soil layer shear wave velocity variation on the ground motion is related
to the amplitude of bedrock input ground motion． Generally，with the increase of input bedrock
peak ground motion， the variances in peak ground acceleration and characteristic period of
response spectrum also increase gradually under different shear wave velocities of soil layers．
( 6) Under the same bedrock input ground motion，the variation of shear wave velocity of soil
layer in the relatively soft soil profile ZK24 has a bigger effect on the peak ground acceleration and
Earthquake Ｒesearch in China
240
the characteristic period of response spectrum than that in profile ZK4． This shows that the impact
of velocity variation on the ground motion is related to soil layer structure，and the shear wave
velocity of soil layers can directly reflect the degree of “softness”and “hardness”of the soils．
The softer the site，the greater the impact will be．
Fig． 5
Effects of variability of the shear wave velocity of soil
layers on peak ground acceleration
Fig． 6
Effects of variability of the shear wave velocity of soil layers on
characteristic period of response spectrum
4
CONCLUSION
Based on the data from typical sites in the Jianghuai region，the influence of shear wave
velocity variation on the peak ground acceleration and the characteristic period of response
spectrum is analyzed with the one-dimensional equivalent linear method． Our results show that:
(1) When the shear wave velocity of soil layers decreases，the peak ground acceleration
decreases gradually，and the long period part of the response spectrum moves to the right，the
long period spectrum value increases generally，and the characteristic period of response spectrum
Volume 28，Number 2
241
increases correspondingly．
(2) When the shear wave velocity of soil layers increases，the peak ground acceleration also
increases gradually，the long period part of response spectrum moves to the left，and it has a
greater effect on the medium and short period part of the response spectrum; the response
spectrum curve moves to the left，and the characteristic period of response spectrum will be
reduced accordingly．
(3) In contrast，the effect of decrease of shear wave velocity of soil layers is slightly larger
than its increase on the peak ground acceleration and the characteristic period of response
spectrum．
(4) The impact degree of velocity variation on the ground motion is related to the spectral
characteristics and amplitude of bedrock input ground motion as well as the soil layer structure of
the site，etc．
Thus，the variation of shear wave velocity of the soil layer has significant influence on the
ground motion． Obtaining objective shear wave velocity data is very important for seismic response
analysis of the soil layer．
This paper has been published in Chinese in the journal of Technology for Earthquake
Disaster Prevention，Volume 8，Number 3，2013．
ＲEFEＲENCES
Chen Guoxing，Liu Xuezhu，Wang Binghui． Effect of variability of soil dynamic parameters on ground motion
parameters for deep soft sites ［J］． Journal of Disaster Prevention and Mitigation Engineering，2007，27(1) :
1 ～ 10( in Chinese with English abstract) ．
Gao Yufeng，Liu Hanlong，Zhu Wei，Gu Changcun． Influences of shear wave velocity on the seismic response of
sand ground ［J］． Geotechnical Investigation ＆ Surveying，2001，1: 39 ～ 42 ( in Chinese with English
abstract) ．
General Administration of Quality Supervision，Inspection and Quarantine of the Peoples Ｒepublic of China．
Evaluation of Seismic Safety for Engineering Sites ( GB17741-2005) ［M］． Beijing: Chinese Standard Press，
2005 ( in Chinese) ．
Hu Yuxian，Gao Mengtan，Du Wei et al． The Teaching Material of Seismic Ground Motion Parameters Zonation
Map of China ［M］． Beijing: Chinese Standard Press，2001. 85 ～ 87( in Chinese) ．
Lan Jingyan，Bo Jingshan，Lv Yuejun． Study on the effect of shear wave velocity on the design spectrum ［J］．
Technology for Earthquake Disaster Prevention，2007，2(1) :19 ～ 24( in Chinese with English abstract) ．
Liao Zhenpeng，Li Xiaojun． A Equivalent Linearization Method for Calculating Earthquake Ｒesponse of Ground
Surface Soil Layers: Earthquake regionalization ( Theory and Practice) ［M］． Beijing: Seismological Press，
1989. 141 ～ 153( in Chinese) ．
Liu Hongshuai，Bo Jingshan，Wu Zhaoying，Liu Dedong． Effects of soil parameters on ground surface peak
acceleration and response spectra ［J］． Journal of Seismological Ｒesearch，2005，28 ( 2 ) : 167 ～ 171 ( in
Chinese with English abstract) ．
Sun Ｒui，Yuan Xiaoming，Liu Xiaojian． Effects of dynamic shear modulus ratio and velocity on surface ground
motion and their equivalent relations ［J］． Chinese Journal of Geotechnical Engineering，2009，31(8) : 1267
～ 1274( in Chinese with English abstract) ．
Yuan Xiaoming，Sun Ｒui，Sun Jing，Meng Shangjiu，Shi Zhaoji． Laboratory experimental study on dynamic shear
modulus ratio and damping ratio of soils ［J］． Journal of Earthquake Engineering and Engineering Vibration，
2000，20(4) :133 ～ 139( in Chinese with English abstract) ．
About the Author
Cao Junfeng，born in 1983， is an engineer at the Earthquake Administration of Anhui
Province． He is mainly engaged in earthquake engineering work． E-mail:caojunfeng2009 @ 126．
com．