- Email: [email protected]
Seismic hazard assessment of the Three Gorges Project
Geodesy and Geodynamics
2013 , 4 ( 2) :53 - 60
http://www. jgg09. com Doi:10.3724/SP.J.1246.2013.02053
Seismic hazard assessment of the Three Gorges Project Yao Ynnsheng, Wang Qiuliang, Li Jinggang, Shen Xueling and Kong Yuyang Key laboratory of Earthquake Geocksy, Institute of Seisrrwlogy, Chi= Earthquake Administration, Wuhan 430071 , China
Abstract : Seismic monitoring data for the past 50 years in the Three Gorges Reservoir area show that the reservoir head area is a typical weak seismic region with low seismicity before impoundment and that the epicenters
were concentrated in the east and west sides of the Zigui Basin, most of which were natural tectonic earth-
quakes. Mter impoundment, the seismic activity shifted to the segment hetween Badong and Zigui along the Yangtze River, mainly within 5 km of the reservoir bank. The seismogenesis was categorized into four types: Karst collapse earthquakes , earthquakes caused by Karst gas explosion, mining tunnel collapse earthquakes , and rock ( terrane) slip earthquakes , all of which are related to the lithology , structure, and tectonics of nearsurface geological bodies of the area. Compared with the seismicity before imponndment, the seismic frequency increase was remarkable, with most of the magnitudes below Ms2. 0. Therefore, the intensity of the earthquakes remained at a low level. On November 22, 2008, a maguitude 4. 1 earthquake, the largest earthquake recorded since impoundment, occurred in Quyuan Town, Zigni County. The intensity and PGA of reservoir-induced earthquakes are higher than those of tectonic earthquakes with equal maguitude , but the peak intensity of reservoir-induced earthquakes is not likely to go beyond that of the estimated range from earlier studies. Key words: Three Gorges Project; reservoir; induced earthquake; seismic hazard assessment
reaches of the Yangtze River. The reservoir is 660 km
1 Introduction
long and 1. 0 - 1. 5 km wide and has a total area of 55000 km 2 and a water surface area of 1048 km2 •
The Three Gorges Reservoir is the largest water conser-
When the water level in the reservoir reaches 175 m,
vancy project for harnessing the Yangtze River, and the
the reservoir can store up to 39. 3 billion m of water.
project has received worldwide attention. The project
The water head has increased nearly 110 m , making it
will be beneficial to the area in many ways. It will help
a large reservoir with a high dam [I] •
3
protect the lower-reaches of the Yangtze River from
Long-term studies on the Yangtze Three Gorges area
flood disasters by regulating the river' s flow, it will
found that the crust in or around the dam site is stable ,
transmit large quantities of clean energy to central and
but a tectonic background exists that could induce seis-
east China, and it will help improve the Yangtze River
mic activity[
shipping conditions.
Therefore, the Reservoir will
greatly benefit the Chinese economy. The Three Gorges Reservoir is a narrow valley reser-
voir that is built in the lower section of the upper Received:2012-11-09; Accepted:2012-11-30
Corresponding author: Yao Yunsheng, E-mail:yunsheng@ public. wh. hh. an '!ln. ...X ,.,.
zm).
""''JUJed
by the CIUna 'lluee Gmg.s Cmpomlioo ( SXSN/
2
J•
The Three Gorges Reservoir area, situ-
ated at the Yangtze Para platform , consists mainly of three types of rock : granite, which the dam is built on, limestone, which exists mainly in the canyon area, and clastic rock, which is the major rock in the river-
bed of the middle-upper reaches['].
We identified
three sets of regional faults ( NE-NNE, NNW -NW, and NWW-oriented) , located at Huangling Anticline and the surrounding area.
54
Geodesy and Geodynamics
Vol.4
The monitoring of recent deformation indicates that
the TGP Reservoir area has been ongoing for the past
these faults twist horizontally at an average speed of
50 years. During this time, a large number of reser-
less than 0. 1 mm/ a, while the average vertical dis-
voir-induced earthquakes have been triggered by the
placement rate is less than 1 mm/ a. However, the
variation of medium stress states, medium physical
faults' function in controlling medium intensity earth-
property, and regional stress fields in the dam area
quakes cannot be ignored. A problem that should be
caused by the impounding and water fluctuation in the
taken into account is that after impoundment , the pres-
reservmr.
sure will rise sharply, thus making water permeate along the faults. This action could possibly trigger a strike-slip displacement and deformation, and could
2
Seismicity monitoring system in the Three Gorges Reservoir area
potentially cause earthquakes. Consequently, the induced earthquake monitoring system was established in
The earthquakes occurring in the TGP Reservoir area
the Three Gorges Reservoir area of the Yangtze River
have been monitored for 50 years , which is a rarity in
by the China Three Gorges Project Corporation. The
the world' s hydropower project history. Currently, the
induced earthquake monitoring system includes a digit-
monitoring system has three pieces. The first piece was
al telemetry seismic network , a crustal deformation mo-
built in 1958 and is composed of 8 seismic stations.
nitoring network, and a well network that observes un-
The second piece was built in the reservoir head area
derground water behavior. A series of scientific studies
in 1997 is composed of 15 attended stations, and can
on reservoir induced earthquake have been conducted
efficiently monitor earthquakes with a magnitude larger
using these
networks[ 4 •5 l.
than 0. 5. The third piece is a digital telemetry seismic
The water level of the Three Gorges Reservoir reached
network that was completed in 2000 and consists of 24
135 m on June 15 , 2003 , and power generation began
telemetric stations ( Fig. 1 ) . Compared to the first two
in July. On May 20 , 2006 , the height of the dam was
analogue systems , the third system has following ad-
increased to 185 m, and on October 27, the water lev-
vantages : a wide dynamic range, high resolution that
el rose to 156 m. On November 5, 2008, the water
can reach up to 3 X 10 -s, a low distortion degree
level reached 172. 30 m. The Three Gorges Project
( usually is 1%o) , easier data storage and exchange ,
( TGP) was finally finished in 2009 , at which time
use of a computer, and the systems' convenient use for
the water level was 175 m. Earthquake monitoring in
seismicity research.
Wuxi
"
...
Liziping
Wushan ~ Fen
1-
··
Legend
J..
Dam
*...
Network center Station
•
30
sr"e~~~'li~
.5" 1fo9.5° E
Figure 1
110.3°E
110.7° E
111.1 o E
Distribution of digital telemetry seismic network in TGP of Yangtze River
111.5 o E
No.2
3
Yao Yunsheng,et al. Seismic hazard assessment of the Three Gorges Project
Seismicity monitoring results in the Three Gorges Reservoir area
55
( M~O) could be detected. During this period, 285 earthquakes were recorded, including 195 with 0 :s;;M
< 1. 0 , 83 with 1. 0 :s:; M < 2. 0, 6 with 2. 0 ::::; M < 3. 0, and 1 earthquake with 3. 0::::; M < 4. 0 (Figs. 2 and 3).
3.1 Seismicity observed in the Three Gorges Reservoir area before impoundment
3. 2
Seismicity monitoring results in the Three Gorges Reservoir area after impoundment
The seismicity recorded in the reservoir head area from 1959 to May 2003 , before impoundment, can be divid-
Since June 1, 2003, the TGP has stored water. From
ed into two stages : before and after the implementation
this time until October 2010, when the water level
of the wireless digital telemetric network. The first
reached 175 m, the water levels can be divided into
stage was from 1959 to 2000, and no information about
three stages. First, the water level gradually increased
earthquakes below a magnitude of 2. 0 could be gath-
to 135 m from June 1 , 2003 to September 19, 2006.
ered due to the equipment sensitivity. During this peri-
The water then rose to 156 m from September 20 , 2006
od, 106 earthquakes with magnitude of 2. 0 or larger
to September 19 , 2008. Finally , the water level has
were recorded. This total included 91 earthquakes of
increased from September 20 , 2008 until its present
2. 0 :s:; M < 3. 0, 12 earthquakes of 3. 0 :s:; M < 4. 0, 2
storage water level of 175 m.
earthquakes of 4. 0 :s;;M < 5. 0, and 1 earthquake stron-
From June 2003 to November 2008 , 5503 earth~0
ger than magnitude 5. 0. The largest event recorded
quakes ( M
during this period had a magnitude of 5. 1 and oc-
seismic network. This total includes 4362 earthquakes
curred in Longhuiguan, Zigui County, on May 22,
of 0. 0 < M < 0. 9, 1030 earthquakes of 1. 0 :s;;M < 2. 0,
1979. The second stage was from 2001 until May 31,
106 earthquakes of 2. 0 :s;;M < 3. 0, and 4 earthquakes
2003 , after the wireless digital telemetric network was
of 3. 0 :s:; M
built and before impoundment. This network allowed
of 4. 1 and occurred in Quyuan Town, Zigui County,
for higher monitoring ability , and smaller earthquakes
on November 22 , 2008 ( Figs. 4 and 5 ) .
) were recorded by the Three Gorges
< 4. 0. The largest event had a magnitude
Nanzftang 0
0
0
110.0° E Figure 2
110.5° E
111.0° E
111.5" E
112.0° E
Distribution of epicenters (M;;;.2. O) in the reservoir head area of TGP from January 1959 to December 2000
56
Vol.4
Geodesy and Geodynamics
.. °
31.5"N
0 0
0
110.0"E
Figure 3
Distribution of epicenters
110.5" E (M~O)
111.0" E
111.5"E
112.0" E
in the reservoir head area of TGP
from January 2001 to May 2003
31.5"N
e
•
•
3l.O"N
30.5"N
30.0" N =.=::..:.:.:....::.:..>::L.J...J_ _ _ 109.0"E 109.5"E 110.0 "E
_ _ J_ _ ___JL>o.....__ __ _ J L . . _ _ - - " . C . _ _ J ' - - - - - - - ' L _ _ _ J
Figure 4
110.5"E
111.0 "E
111.5"E
112.0"E
Distribution of epicenters (M~O) in the reservoir head area of TGP from June 2003 to November 2008
Compared to the earthquakes that occurred before impoundment, the seismic frequency has obviously increased after the reservoir began to store water. However, most of these magnitudes have been below Ms2. 0.
3. 3
Special distribution characteristics of seismic activity in the Three Gorges Reservoir area after impoundment
Two earthquakes with a magnitude of 3. 8 and 3. 5 oc-
Since June 2003 when the Three Gorges Reservoir be-
curred in Badong in 2004 and 2005, respectively, and
gan to store water , the earthquakes in the reservoir
one earthquake with a magnitude of 4. 1 occurred in
head area have been centered on the middle segment in
Zigui in 2008. These three earthquakes occurred after
the reservoir region along the Yangtze River of Badong
impoundment , indicating that the Three Gorges Reser-
and Zigui Counties ( Figs. 4 and 5 ) and were several
voir area is still in a state of weak seismicity.
kilometers away from reservoir boundary. Furthermore,
No.2
57
Yao Yunsheng, et al. Seismic hazard assessment of the Three Gorges Project
mately 135 m in June 2003, rose to 156 m on October
most of the earthquakes have occurred more than 30 to 6
70 kilometers away from reservoir dam site[ J.
27 , 2006, and finally increased to 172 m on November
The water storage of the Three Gorges Reservoir has
4, 2008.
experienced three stages: the water level was approxi-
As shown in figure 6, from the 135 m water storage
.
Nanzhang
31.5° N
•
•
•
••
•
•
Fengjie 31.0°N
• 30.5°N
Legend • M2.0-2.9(106 M3.0-3.9(4)
30.00 N • M4.0-4.9(1) 109.0° E 109.5° E
110.0° E
110.5 o E
111.0° E
112.0° E
111.5" E
Distribution of epicenters ( M ~ 2. 0) in the reservoir head area of TGP
Figure 5
from June 2003 to November 2008
175.1
j~;l
207
1077
~h~.!!it!:~!ill!!~~~I!!!!!l!1!1!W!!l!W!!!l!!rr~I!!!!l.!J.t!!j~~!!:':::_---, 2003
2004
2005
4
2006
2007 2008 Time(year)
2009
l~l·· · ····~ru·~ 10°
2010
2011
·. . I
1
0.0
1.0
2.0
3.0
2012
•
4.0
5.0
a=4.713, b=1.1536, R=-0.9938, M=0.7-4.4 Figure 6
Water level in the front of the Three Gorges Reservoir and seismic parameters of the region of the key monitored area along the Yangtze River
58
Vol.4
Geodesy and Geodynamics
period to the 156 m period, the seismic magnitude increased gradually, and then stabilized. The frequency of earthquakes of M
;:?!:
2. 0 rose sharply compared to
that in the first period, especially from July 2007 to September 2008. The largest earthquake since impoundment was recorded 17 days after water storage was over 172 m, with a magnitude of 4. 1 Ms and a b value of 1. 1622. The earthquake occurred in Quyuan Town, Zigui , and showed the apparent characteristics of a reservoir-induced earthquake[ 7 J.
3. 4
Type of induced earthquakes in the Three Gorges Reservoir
The aims of this comprehensive analysis were to correlate the spatio-temporal distribution of earthquakes be-
Figure 7
The seismic intensity diagram of M5. 1 in
Longhuiguan area around TGP in 1979
fore and after impoundment ; to investigate the strata , 26
lithology, and hydrological condition of the epicenter; and to correlate the reservoir water level with the inten-
52km
Zhengjiawan
sity and frequency of earthquakes. From this analysis, it was concluded that the earthquakes occurring in the Three Gorges Reservoir area are typical reservoir-induced earthquakes related closely to impoundment, the earthquakes ' magnitudes are small due to their shallow source , and most of the epicenters are located 5 km away from the reservoir bank[ 8 J.
4
The survey of earthquake disaster
In the reservoir head area, no middle-strong earthquakes in history were recorded before impoundment.
Zhaojiawan
_/ Xikouping Riyueping
Only one earthquake with a magnitude of 5. 1 was recorded after modem equipment was set up ( the seismic intensity diagram lines are shown in figure 7 ) .
Figure 8
The seismic intensity V and VI of M4. 1 in Quyuanzhen area of in TGP in 2008
The largest earthquake since impoundment in June 2003 had a magnitude of 4. 1 and was induced in the Three Gorges Reservoir ( Fig. 8) .
5
The attenuation relationship of the ground motion parameter
Kong[ 9 J fit the attenuation relationship of the ground motion parameter ( intensity, PGV) in the Three Gor-
Long axis: Ia =6. 037 + 1. 014M1.512ln(R+16)
u=0.432
(1)
Narrow axis: lb = 4. 289 + 0. 968M1. 169ln(R +7)
£T
=0. 441 (2)
Using data for 27 reservoir-induced earthquakes from around the world , we obtained the intensity attenuation relationship of reservoir-induced earthquakes.
ges Reservoir area and of reservoir-induced seismicity. The seismic intensity attenuation relationships of tectonic earthquakes in the Three Gorges area are :
Long axis: Ia = 5. 002 + 0. 9722M1.324In(R+6)
u=0.614
(3)
59
Yao Yunsheng,et al. Seismic hazard assessment of the Tirree Gorges Project
No.2
Narrow axis: Ib = 4. 425 + 0. 9028M-
1. 204ln(R +4)
Narrow axis: lgya = 1. 471 +
a =0. 537 (4)
0.3545M-1.444ln(R+4) (8)
The PGA attenuation relationship of tectonic earth-
The comparison results show that the intensity of res-
quakes in the Three Gorges area :
ervoir-induced earthquakes is higher than that of equal magnitude natural tectonic earthquakes when the mag-
Long axis: lgy a = 1. 860 + 0. 398M -
nitude is low. The intensity of reservoir-induced earth-
1. 608lg( R + 10)
(5)
quakes is not obviously high when the magnitude increases. Reservoir-induced earthquakes also have fast
Narrow axis: lgyb = 1. 403 + 0. 380M-
attenuation and small affected areas.
(6)
1. 405lg(R +6)
6
Conclusions
The PGA attenuation relationship of reservoir-inOn the basis of the comprehensive analysis of the inten-
duced earthquakes:
sity and frequency of earthquakes before and after imLong axis: lgy a = 1. 629 + 0. 382M -
pounding, we drew the following conclusions. Mter
(7)
1. 518ln(R +5)
10
impoundment , most of the earthquakes occurring in the
9
9
- -
Reservoir earthquake Natural earthquake
4
4
3 0
- -
Reservoir earthquake Natural earthquake
0.5
1.0
1.5
2.0
2.5
3.0
3 0
0.5
Figure 9
1.5
3.0
(lgR) Narrow axis
x(lgR) Long axis
X
The seismic intensity attenuation compare curve of tectonic earthquake and reservoir-induced earthquake in Tirree Gorges area.
4.0
4.0
3.5
3.5 - -
3.0
Reservoir earthquake Natural earthquake
3.0
1.0 0.5
0.5
00~--~--~~~~~~~~~~
0.5
1.0
3.0
00~--~--~~~~~~~~~~
3~
0.5
Narrow axis
Figure 10
Comparison of PGA attenuation of tectonic earthquakes and
reservoir-induced earthquakes in the Three Gorges area
60
Geodesy and Geodynamics
Three Gorges Reservoir area were typical reservoir-in-
[2]
Li Shengle, Yan Zunguo , Xue Junrong, et al. First micro-quake swarm activity since storage in Three Gorges Reservoir. Journal of
duced earthquakes related closely to impoundment. The seismic activity was concentrated in the middle
Vol.4
Geodesy and Geodynamics, 2003, 23(4) :75-79. (in Chinese) [ 3]
Gao Shijun, et al. Crustal stress field and seismic activity in the
segment of the reservoir region along the Yangtze River
Three Gorges area. Beijing: Seismological Press, 1992. ( in Chi-
and 5 km away from the reservoir bank. Reservoir-in-
....,)
duced earthquakes have shallow sources, high intensi-
[ 4]
ties, quick attenuation , and smaller affected areas.
voir". Recent Developments in World Seismology, 2006(9) :67-
The strength of earthquake activity remained at a low level before aod after the impoundment in the Three
Yao Yunsheng. Introduction of the program "monitoring and studies for reservoir-induced earthquakes in the Three Gorge Reser-
69 ( in Chinese) ,
[5]
Yao Yunsheng, Zhang Lifen , Wang Qiuliang, et al. Impact of the
Gorges area, with the magnitude of the largest earth-
resenroir induced earthquake on Three Gorge Project. 14WCEE,
quake being approximately 5. 0. The intensity and
10, 2008, Beijing.
PGA of reservoir-induced earthquakes are higher than
[6]
that of equal magnitude natural tectonic earthquakes when the magnitude is low. However, the intensity and
Wang Qiuliang,Yao Yunsheng, Xia Jinwu,et al. Study on meth-
ods of resenroir induced earthquake prediction of the Three Gorge Reservoir. 14WCEE ,10,2008, Beijing. [7]
PGA of reservoir-induced earthquakes are not obviously
Wang Qingyun, Zhang Qiuwen and li Feng. Study on risk of induced earthquake in reservoir head region of Three Gorges projec-
high when the magnitude increases. Therefore, we
tion on Yangtze River. Journal of Geodesy and Geodynamics,
confirm that the intensity of earthquakes goes beyond
2003, 23(2) ,101-106. (;n Chi....,)
the estimated raoge from earlier studies.
[ 8]
Chen ShujlUl, Su AijWl and :Wo Dengui. Genesis and type of induced earthquake in Three Gorge Reservoir. Journal of Geodesy and Geodynamics , 2004 , 24 ( 2) :70 - 73 . ( in Chinese)
References
[9]
Kong Yuyang. Study on attenuation relationship of reservoir induced earthquakes. Wuhan: Institute of Seismology, China Earth-
[ 1]
Wang Rushu. Balancing environment and development. International Water Power & Dam Construction, 2003(3) :34-38.
quake Adminstration,2006. (in Chinese)
2013 , 4 ( 2) :53 - 60
http://www. jgg09. com Doi:10.3724/SP.J.1246.2013.02053
Seismic hazard assessment of the Three Gorges Project Yao Ynnsheng, Wang Qiuliang, Li Jinggang, Shen Xueling and Kong Yuyang Key laboratory of Earthquake Geocksy, Institute of Seisrrwlogy, Chi= Earthquake Administration, Wuhan 430071 , China
Abstract : Seismic monitoring data for the past 50 years in the Three Gorges Reservoir area show that the reservoir head area is a typical weak seismic region with low seismicity before impoundment and that the epicenters
were concentrated in the east and west sides of the Zigui Basin, most of which were natural tectonic earth-
quakes. Mter impoundment, the seismic activity shifted to the segment hetween Badong and Zigui along the Yangtze River, mainly within 5 km of the reservoir bank. The seismogenesis was categorized into four types: Karst collapse earthquakes , earthquakes caused by Karst gas explosion, mining tunnel collapse earthquakes , and rock ( terrane) slip earthquakes , all of which are related to the lithology , structure, and tectonics of nearsurface geological bodies of the area. Compared with the seismicity before imponndment, the seismic frequency increase was remarkable, with most of the magnitudes below Ms2. 0. Therefore, the intensity of the earthquakes remained at a low level. On November 22, 2008, a maguitude 4. 1 earthquake, the largest earthquake recorded since impoundment, occurred in Quyuan Town, Zigni County. The intensity and PGA of reservoir-induced earthquakes are higher than those of tectonic earthquakes with equal maguitude , but the peak intensity of reservoir-induced earthquakes is not likely to go beyond that of the estimated range from earlier studies. Key words: Three Gorges Project; reservoir; induced earthquake; seismic hazard assessment
reaches of the Yangtze River. The reservoir is 660 km
1 Introduction
long and 1. 0 - 1. 5 km wide and has a total area of 55000 km 2 and a water surface area of 1048 km2 •
The Three Gorges Reservoir is the largest water conser-
When the water level in the reservoir reaches 175 m,
vancy project for harnessing the Yangtze River, and the
the reservoir can store up to 39. 3 billion m of water.
project has received worldwide attention. The project
The water head has increased nearly 110 m , making it
will be beneficial to the area in many ways. It will help
a large reservoir with a high dam [I] •
3
protect the lower-reaches of the Yangtze River from
Long-term studies on the Yangtze Three Gorges area
flood disasters by regulating the river' s flow, it will
found that the crust in or around the dam site is stable ,
transmit large quantities of clean energy to central and
but a tectonic background exists that could induce seis-
east China, and it will help improve the Yangtze River
mic activity[
shipping conditions.
Therefore, the Reservoir will
greatly benefit the Chinese economy. The Three Gorges Reservoir is a narrow valley reser-
voir that is built in the lower section of the upper Received:2012-11-09; Accepted:2012-11-30
Corresponding author: Yao Yunsheng, E-mail:yunsheng@ public. wh. hh. an '!ln. ...X ,.,.
zm).
""''JUJed
by the CIUna 'lluee Gmg.s Cmpomlioo ( SXSN/
2
J•
The Three Gorges Reservoir area, situ-
ated at the Yangtze Para platform , consists mainly of three types of rock : granite, which the dam is built on, limestone, which exists mainly in the canyon area, and clastic rock, which is the major rock in the river-
bed of the middle-upper reaches['].
We identified
three sets of regional faults ( NE-NNE, NNW -NW, and NWW-oriented) , located at Huangling Anticline and the surrounding area.
54
Geodesy and Geodynamics
Vol.4
The monitoring of recent deformation indicates that
the TGP Reservoir area has been ongoing for the past
these faults twist horizontally at an average speed of
50 years. During this time, a large number of reser-
less than 0. 1 mm/ a, while the average vertical dis-
voir-induced earthquakes have been triggered by the
placement rate is less than 1 mm/ a. However, the
variation of medium stress states, medium physical
faults' function in controlling medium intensity earth-
property, and regional stress fields in the dam area
quakes cannot be ignored. A problem that should be
caused by the impounding and water fluctuation in the
taken into account is that after impoundment , the pres-
reservmr.
sure will rise sharply, thus making water permeate along the faults. This action could possibly trigger a strike-slip displacement and deformation, and could
2
Seismicity monitoring system in the Three Gorges Reservoir area
potentially cause earthquakes. Consequently, the induced earthquake monitoring system was established in
The earthquakes occurring in the TGP Reservoir area
the Three Gorges Reservoir area of the Yangtze River
have been monitored for 50 years , which is a rarity in
by the China Three Gorges Project Corporation. The
the world' s hydropower project history. Currently, the
induced earthquake monitoring system includes a digit-
monitoring system has three pieces. The first piece was
al telemetry seismic network , a crustal deformation mo-
built in 1958 and is composed of 8 seismic stations.
nitoring network, and a well network that observes un-
The second piece was built in the reservoir head area
derground water behavior. A series of scientific studies
in 1997 is composed of 15 attended stations, and can
on reservoir induced earthquake have been conducted
efficiently monitor earthquakes with a magnitude larger
using these
networks[ 4 •5 l.
than 0. 5. The third piece is a digital telemetry seismic
The water level of the Three Gorges Reservoir reached
network that was completed in 2000 and consists of 24
135 m on June 15 , 2003 , and power generation began
telemetric stations ( Fig. 1 ) . Compared to the first two
in July. On May 20 , 2006 , the height of the dam was
analogue systems , the third system has following ad-
increased to 185 m, and on October 27, the water lev-
vantages : a wide dynamic range, high resolution that
el rose to 156 m. On November 5, 2008, the water
can reach up to 3 X 10 -s, a low distortion degree
level reached 172. 30 m. The Three Gorges Project
( usually is 1%o) , easier data storage and exchange ,
( TGP) was finally finished in 2009 , at which time
use of a computer, and the systems' convenient use for
the water level was 175 m. Earthquake monitoring in
seismicity research.
Wuxi
"
...
Liziping
Wushan ~ Fen
1-
··
Legend
J..
Dam
*...
Network center Station
•
30
sr"e~~~'li~
.5" 1fo9.5° E
Figure 1
110.3°E
110.7° E
111.1 o E
Distribution of digital telemetry seismic network in TGP of Yangtze River
111.5 o E
No.2
3
Yao Yunsheng,et al. Seismic hazard assessment of the Three Gorges Project
Seismicity monitoring results in the Three Gorges Reservoir area
55
( M~O) could be detected. During this period, 285 earthquakes were recorded, including 195 with 0 :s;;M
< 1. 0 , 83 with 1. 0 :s:; M < 2. 0, 6 with 2. 0 ::::; M < 3. 0, and 1 earthquake with 3. 0::::; M < 4. 0 (Figs. 2 and 3).
3.1 Seismicity observed in the Three Gorges Reservoir area before impoundment
3. 2
Seismicity monitoring results in the Three Gorges Reservoir area after impoundment
The seismicity recorded in the reservoir head area from 1959 to May 2003 , before impoundment, can be divid-
Since June 1, 2003, the TGP has stored water. From
ed into two stages : before and after the implementation
this time until October 2010, when the water level
of the wireless digital telemetric network. The first
reached 175 m, the water levels can be divided into
stage was from 1959 to 2000, and no information about
three stages. First, the water level gradually increased
earthquakes below a magnitude of 2. 0 could be gath-
to 135 m from June 1 , 2003 to September 19, 2006.
ered due to the equipment sensitivity. During this peri-
The water then rose to 156 m from September 20 , 2006
od, 106 earthquakes with magnitude of 2. 0 or larger
to September 19 , 2008. Finally , the water level has
were recorded. This total included 91 earthquakes of
increased from September 20 , 2008 until its present
2. 0 :s:; M < 3. 0, 12 earthquakes of 3. 0 :s:; M < 4. 0, 2
storage water level of 175 m.
earthquakes of 4. 0 :s;;M < 5. 0, and 1 earthquake stron-
From June 2003 to November 2008 , 5503 earth~0
ger than magnitude 5. 0. The largest event recorded
quakes ( M
during this period had a magnitude of 5. 1 and oc-
seismic network. This total includes 4362 earthquakes
curred in Longhuiguan, Zigui County, on May 22,
of 0. 0 < M < 0. 9, 1030 earthquakes of 1. 0 :s;;M < 2. 0,
1979. The second stage was from 2001 until May 31,
106 earthquakes of 2. 0 :s;;M < 3. 0, and 4 earthquakes
2003 , after the wireless digital telemetric network was
of 3. 0 :s:; M
built and before impoundment. This network allowed
of 4. 1 and occurred in Quyuan Town, Zigui County,
for higher monitoring ability , and smaller earthquakes
on November 22 , 2008 ( Figs. 4 and 5 ) .
) were recorded by the Three Gorges
< 4. 0. The largest event had a magnitude
Nanzftang 0
0
0
110.0° E Figure 2
110.5° E
111.0° E
111.5" E
112.0° E
Distribution of epicenters (M;;;.2. O) in the reservoir head area of TGP from January 1959 to December 2000
56
Vol.4
Geodesy and Geodynamics
.. °
31.5"N
0 0
0
110.0"E
Figure 3
Distribution of epicenters
110.5" E (M~O)
111.0" E
111.5"E
112.0" E
in the reservoir head area of TGP
from January 2001 to May 2003
31.5"N
e
•
•
3l.O"N
30.5"N
30.0" N =.=::..:.:.:....::.:..>::L.J...J_ _ _ 109.0"E 109.5"E 110.0 "E
_ _ J_ _ ___JL>o.....__ __ _ J L . . _ _ - - " . C . _ _ J ' - - - - - - - ' L _ _ _ J
Figure 4
110.5"E
111.0 "E
111.5"E
112.0"E
Distribution of epicenters (M~O) in the reservoir head area of TGP from June 2003 to November 2008
Compared to the earthquakes that occurred before impoundment, the seismic frequency has obviously increased after the reservoir began to store water. However, most of these magnitudes have been below Ms2. 0.
3. 3
Special distribution characteristics of seismic activity in the Three Gorges Reservoir area after impoundment
Two earthquakes with a magnitude of 3. 8 and 3. 5 oc-
Since June 2003 when the Three Gorges Reservoir be-
curred in Badong in 2004 and 2005, respectively, and
gan to store water , the earthquakes in the reservoir
one earthquake with a magnitude of 4. 1 occurred in
head area have been centered on the middle segment in
Zigui in 2008. These three earthquakes occurred after
the reservoir region along the Yangtze River of Badong
impoundment , indicating that the Three Gorges Reser-
and Zigui Counties ( Figs. 4 and 5 ) and were several
voir area is still in a state of weak seismicity.
kilometers away from reservoir boundary. Furthermore,
No.2
57
Yao Yunsheng, et al. Seismic hazard assessment of the Three Gorges Project
mately 135 m in June 2003, rose to 156 m on October
most of the earthquakes have occurred more than 30 to 6
70 kilometers away from reservoir dam site[ J.
27 , 2006, and finally increased to 172 m on November
The water storage of the Three Gorges Reservoir has
4, 2008.
experienced three stages: the water level was approxi-
As shown in figure 6, from the 135 m water storage
.
Nanzhang
31.5° N
•
•
•
••
•
•
Fengjie 31.0°N
• 30.5°N
Legend • M2.0-2.9(106 M3.0-3.9(4)
30.00 N • M4.0-4.9(1) 109.0° E 109.5° E
110.0° E
110.5 o E
111.0° E
112.0° E
111.5" E
Distribution of epicenters ( M ~ 2. 0) in the reservoir head area of TGP
Figure 5
from June 2003 to November 2008
175.1
j~;l
207
1077
~h~.!!it!:~!ill!!~~~I!!!!!l!1!1!W!!l!W!!!l!!rr~I!!!!l.!J.t!!j~~!!:':::_---, 2003
2004
2005
4
2006
2007 2008 Time(year)
2009
l~l·· · ····~ru·~ 10°
2010
2011
·. . I
1
0.0
1.0
2.0
3.0
2012
•
4.0
5.0
a=4.713, b=1.1536, R=-0.9938, M=0.7-4.4 Figure 6
Water level in the front of the Three Gorges Reservoir and seismic parameters of the region of the key monitored area along the Yangtze River
58
Vol.4
Geodesy and Geodynamics
period to the 156 m period, the seismic magnitude increased gradually, and then stabilized. The frequency of earthquakes of M
;:?!:
2. 0 rose sharply compared to
that in the first period, especially from July 2007 to September 2008. The largest earthquake since impoundment was recorded 17 days after water storage was over 172 m, with a magnitude of 4. 1 Ms and a b value of 1. 1622. The earthquake occurred in Quyuan Town, Zigui , and showed the apparent characteristics of a reservoir-induced earthquake[ 7 J.
3. 4
Type of induced earthquakes in the Three Gorges Reservoir
The aims of this comprehensive analysis were to correlate the spatio-temporal distribution of earthquakes be-
Figure 7
The seismic intensity diagram of M5. 1 in
Longhuiguan area around TGP in 1979
fore and after impoundment ; to investigate the strata , 26
lithology, and hydrological condition of the epicenter; and to correlate the reservoir water level with the inten-
52km
Zhengjiawan
sity and frequency of earthquakes. From this analysis, it was concluded that the earthquakes occurring in the Three Gorges Reservoir area are typical reservoir-induced earthquakes related closely to impoundment, the earthquakes ' magnitudes are small due to their shallow source , and most of the epicenters are located 5 km away from the reservoir bank[ 8 J.
4
The survey of earthquake disaster
In the reservoir head area, no middle-strong earthquakes in history were recorded before impoundment.
Zhaojiawan
_/ Xikouping Riyueping
Only one earthquake with a magnitude of 5. 1 was recorded after modem equipment was set up ( the seismic intensity diagram lines are shown in figure 7 ) .
Figure 8
The seismic intensity V and VI of M4. 1 in Quyuanzhen area of in TGP in 2008
The largest earthquake since impoundment in June 2003 had a magnitude of 4. 1 and was induced in the Three Gorges Reservoir ( Fig. 8) .
5
The attenuation relationship of the ground motion parameter
Kong[ 9 J fit the attenuation relationship of the ground motion parameter ( intensity, PGV) in the Three Gor-
Long axis: Ia =6. 037 + 1. 014M1.512ln(R+16)
u=0.432
(1)
Narrow axis: lb = 4. 289 + 0. 968M1. 169ln(R +7)
£T
=0. 441 (2)
Using data for 27 reservoir-induced earthquakes from around the world , we obtained the intensity attenuation relationship of reservoir-induced earthquakes.
ges Reservoir area and of reservoir-induced seismicity. The seismic intensity attenuation relationships of tectonic earthquakes in the Three Gorges area are :
Long axis: Ia = 5. 002 + 0. 9722M1.324In(R+6)
u=0.614
(3)
59
Yao Yunsheng,et al. Seismic hazard assessment of the Tirree Gorges Project
No.2
Narrow axis: Ib = 4. 425 + 0. 9028M-
1. 204ln(R +4)
Narrow axis: lgya = 1. 471 +
a =0. 537 (4)
0.3545M-1.444ln(R+4) (8)
The PGA attenuation relationship of tectonic earth-
The comparison results show that the intensity of res-
quakes in the Three Gorges area :
ervoir-induced earthquakes is higher than that of equal magnitude natural tectonic earthquakes when the mag-
Long axis: lgy a = 1. 860 + 0. 398M -
nitude is low. The intensity of reservoir-induced earth-
1. 608lg( R + 10)
(5)
quakes is not obviously high when the magnitude increases. Reservoir-induced earthquakes also have fast
Narrow axis: lgyb = 1. 403 + 0. 380M-
attenuation and small affected areas.
(6)
1. 405lg(R +6)
6
Conclusions
The PGA attenuation relationship of reservoir-inOn the basis of the comprehensive analysis of the inten-
duced earthquakes:
sity and frequency of earthquakes before and after imLong axis: lgy a = 1. 629 + 0. 382M -
pounding, we drew the following conclusions. Mter
(7)
1. 518ln(R +5)
10
impoundment , most of the earthquakes occurring in the
9
9
- -
Reservoir earthquake Natural earthquake
4
4
3 0
- -
Reservoir earthquake Natural earthquake
0.5
1.0
1.5
2.0
2.5
3.0
3 0
0.5
Figure 9
1.5
3.0
(lgR) Narrow axis
x(lgR) Long axis
X
The seismic intensity attenuation compare curve of tectonic earthquake and reservoir-induced earthquake in Tirree Gorges area.
4.0
4.0
3.5
3.5 - -
3.0
Reservoir earthquake Natural earthquake
3.0
1.0 0.5
0.5
00~--~--~~~~~~~~~~
0.5
1.0
3.0
00~--~--~~~~~~~~~~
3~
0.5
Narrow axis
Figure 10
Comparison of PGA attenuation of tectonic earthquakes and
reservoir-induced earthquakes in the Three Gorges area
60
Geodesy and Geodynamics
Three Gorges Reservoir area were typical reservoir-in-
[2]
Li Shengle, Yan Zunguo , Xue Junrong, et al. First micro-quake swarm activity since storage in Three Gorges Reservoir. Journal of
duced earthquakes related closely to impoundment. The seismic activity was concentrated in the middle
Vol.4
Geodesy and Geodynamics, 2003, 23(4) :75-79. (in Chinese) [ 3]
Gao Shijun, et al. Crustal stress field and seismic activity in the
segment of the reservoir region along the Yangtze River
Three Gorges area. Beijing: Seismological Press, 1992. ( in Chi-
and 5 km away from the reservoir bank. Reservoir-in-
....,)
duced earthquakes have shallow sources, high intensi-
[ 4]
ties, quick attenuation , and smaller affected areas.
voir". Recent Developments in World Seismology, 2006(9) :67-
The strength of earthquake activity remained at a low level before aod after the impoundment in the Three
Yao Yunsheng. Introduction of the program "monitoring and studies for reservoir-induced earthquakes in the Three Gorge Reser-
69 ( in Chinese) ,
[5]
Yao Yunsheng, Zhang Lifen , Wang Qiuliang, et al. Impact of the
Gorges area, with the magnitude of the largest earth-
resenroir induced earthquake on Three Gorge Project. 14WCEE,
quake being approximately 5. 0. The intensity and
10, 2008, Beijing.
PGA of reservoir-induced earthquakes are higher than
[6]
that of equal magnitude natural tectonic earthquakes when the magnitude is low. However, the intensity and
Wang Qiuliang,Yao Yunsheng, Xia Jinwu,et al. Study on meth-
ods of resenroir induced earthquake prediction of the Three Gorge Reservoir. 14WCEE ,10,2008, Beijing. [7]
PGA of reservoir-induced earthquakes are not obviously
Wang Qingyun, Zhang Qiuwen and li Feng. Study on risk of induced earthquake in reservoir head region of Three Gorges projec-
high when the magnitude increases. Therefore, we
tion on Yangtze River. Journal of Geodesy and Geodynamics,
confirm that the intensity of earthquakes goes beyond
2003, 23(2) ,101-106. (;n Chi....,)
the estimated raoge from earlier studies.
[ 8]
Chen ShujlUl, Su AijWl and :Wo Dengui. Genesis and type of induced earthquake in Three Gorge Reservoir. Journal of Geodesy and Geodynamics , 2004 , 24 ( 2) :70 - 73 . ( in Chinese)
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[9]
Kong Yuyang. Study on attenuation relationship of reservoir induced earthquakes. Wuhan: Institute of Seismology, China Earth-
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quake Adminstration,2006. (in Chinese)