CORRELATION BETWEEN WATER LEVEL DECREASE IN ATATURK DAM, TURKEY

and Mw 5.0 EARTHQUAKE ON SEPTEMBER 3, 2008

 

Haluk EYİDOĞAN, Veli GEÇGEL and Zumer PABUÇCUe mail: eyidogan@itu.edu.tr

The examination of earthquake triggering mechanism of Atatürk dam area, the space and time distribution of the epicenters and solutions of the fault mechanisms belonging to the earthquake occurred in September 3, 2008 (02:2 UTC, ML=5.2) and its aftershocks (ML=4.6 and ML=4.0), and their correlation with the surrounding tectonic structure.

OBJECTIVE

Atatürk Dam Features

• Atatürk Dam is on the Fırat (Euphrates) river and is the fourth biggest clay cored rock-fill dam in the world regarding water capacity and amount of electricity produced.

• The main features of the dam are as follows: Dam height – 170m; Crest length – 1670m; Crest level – 549m; Maximum base width – approx. 900m; Dam volume – 84 x 106m3; Reservoir volume – 48 km3; Resrvoir area- 817 km2; Installed capacity – 2400MW; Annual energy generation – 8100GWh.

• The maximum and minimum operation reservoir levels are 542m and 526m asl respectively.

Tectonic development of the area is

governed by convergence of the

Arabian and African Plates towards

the Anatolian Plate. The Atatürk Dam

is located at 50 km southeast of East

Anatolian Fault zone which is the

most prominent structural elements in

the region. Bozova Fault was issued

on the Active Fault Map of Turkey in

1992 and Geology Map of Turkey.

Right-lateral strike-slip Bozova Fault

is located 1.5 km south of the dam

and has a length of about 55-60 km

The dam was started to be filled following the year of 1989. The reservoir level reached 535m asl in March 1994 and has varied between 526m and 537m asl since then. The maximum and minimum operation reservoir levels are 542m and 526m asl, respectively.

Atatürk Dam site has no large seismic activity in historical periods. It was seen that the triggered earthquake activity, obtained from the Kandilli Observatory and Earthquake Research Institute (KOERI) database, was evidently increasing following the year of 1994. Although KOERI stations are distant and few in number, the frequency of the earthquakes increased rapidly since 1994 following the highest level of water reach in the dam.

2

2,5

3

3,5

4

4,5

5

01.0

1.19

85

01.0

1.19

86

01.0

1.19

87

01.0

1.19

88

01.0

1.19

89

01.0

1.19

90

01.0

1.19

91

01.0

1.19

92

01.0

1.19

93

01.0

1.19

94

01.0

1.19

95

01.0

1.19

96

01.0

1.19

97

01.0

1.19

98

01.0

1.19

99

01.0

1.20

00

01.0

1.20

01

01.0

1.20

02

01.0

1.20

03

01.0

1.20

04

01.0

1.20

05

01.0

1.20

06

01.0

1.20

07

01.0

1.20

08

Time

Mag

nitu

de

0

100

200

300

400

500

600

Wat

er L

evel

in M

eter

s

31.1

2.20

08

Missing Data ?

0

5

10

15

20

25

30

35

40

01.01.1992 01.01.1994 01.01.2000 01.01.2004 01.01.2006 01.01.2007 01.01.2008 31.05.2009

Time (Year)

Num

ber o

f St

atio

ns

0

5

10

15

20

25

30

35

40

Cum

ulat

ive

Num

ber o

f Sta

tions

Number of the earthquake stations present in the area of 1x1 degree

The number of the earthquake stations did not undergo a great change until the TURDEP project activities (Inan et al., 2007) started for the region. 30 seismic stations were installed in the region, mainly along the EAFZ. This helped to increase the accuracy of the EQ parameters for the activity around the dam.

Fault mechanism solutions of the earthquakes with a magnitude of ML≥ 4.0 and the seismicity in the time period

between 2007-2009 (TURDEP Project Database)

1 1.5 2 2.5 3 3.5 4 4.5 529-Nov-06

17-Jun-07

3-Jan-08

21-Jul-08

6-Feb-09

25-Aug-09

13-Mar-10

Time vs Magnitude (2007-2009)

0.00 0.20 0.40 0.60 0.80 1.000

1

2

3

4

5

Md vs RMS Residuals

Md

The water level decreased rapidly in the summer of 2007, did not increase in the 2008 winter because of insufficient rainfall, and decreased even more in the summer of 2008. On September 3, 2008, in the days when the total decrease was 6 m, an earthquake with a magnitude of Mw=5.0 (ML=5.2) occurred in the northeast of the body of the dam; and aftershocks were experienced following the earthquake.

01/0

1/20

07

01/0

3/20

07

01/0

5/20

07

01/0

7/20

07

01/0

9/20

07

01/1

1/20

07

01/0

1/20

08

01/0

3/20

08

01/0

5/20

08

01/0

7/20

08

01/0

9/20

08

01/1

1/20

08

01/0

1/20

09

01/0

3/20

09

01/0

5/20

09

01/0

7/20

09

01/0

9/20

09

01/1

1/20

091.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

525

526

527

528

529

530

531

532

533

534

535

536

537

3 September 2008Mw=5.0

Time

Magnitude

Wat

er L

evel

in M

eter

s

817 km2 x 6.25 mAmount of drawdown ≈ 5 billion ton

* The strike slip mechanism at the ATATÜRK DAM site is due to shear-slip long the existing fractures as a result of increased maximum or minimum principal stresses.

* Shear stress in the region is probably close to the rock-mass frictional strengths and that a small perturbation of the shear stress field triggered the magnitude 5.0 activity.

σ R =σL – σS

σ3σ1Water level

σ1>σ3

N

CONCLUSIONS

• Considering the stress changes caused by the mechanism characteristics of the September 3, 2008 earthquake, ambient stress distrubition in the region, the locations of the aftershocks, and drastic decrease in the water level, the earthquake occurred on September 3, 2008 was interpreted as a triggered earthquake

• It could be stated that fast and significant amount of water load decrease in the Ataturk Dam caused the exceeding of the critical tension level by changing the ambient NW-SE directioned compressional stress or NE-SW directioned tensional stress and finally caused an earthquake with a magnitude of Mw=5.0.

CONCLUSIONS

• No concrete conclusion was reached regarding the correlation of the triggered seismicity, consisting of September 3, 2008 earthquake and its aftershocks, with the active Bozova Fault.

• It should be pointed out that the possibility that new changes in the tectonic forces around the dam and in depths and pore pressure, due to the water level changes in significant amounts, would cause stress effects that would trigger the Bozova Fault should be evaluated. The Bozova Fault that is located significantly close to the body of the dam should be urgently and multi-dimensionally examined.

We would like to offer our acknowledgements to Turkish Directory of State Water Affairs (DSI) and TUBITAK Marmara Research Center-Institute of Earth and Marine Science (MRC-IEMS) for their support for data. Zumer Pabuccu and Onur Tan made contributions for the acquisition of raw data, Aylin Tan spent efforts to supply some articles and documents and Argun Kocaoglu helped in installing and compiling softwares on my computer.

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