Document Type : Original Research Paper

Authors

1 Mining Engineering Department, Sahand University of Technology, Tabriz, Iran

2 Mining Engineering Department, Amirkabir University of Technology, Tehran, Iran

3 Institute of Geophysics, Tehran University, Tehran, Iran

Abstract

Seismic travel time tomography uses seismic waves to image velocity distribution inside the ground. This method has been widely applied to practical applications in many fields including earth sciences. In this method, first-arrival times of seismic waves due to artificial sources, observed at receivers in the vicinity of the exploration target are analyzed to obtain the velocity distribution within the propagation area. This paper describes the seismic tomography investigation performed at the abutments of Bakhtyari Dam site. The study aimed to find the low-velocity zones that may correspond to jointed media where seepage most likely happens. We performed 3-D tomographic inversion on Bakhtiari dam seismic data. To perform ray tracing and travel-time computation at each iteration, we used Um and Thurber (1987) method and for inversion step we used SIRT method. In most of the tomograms, average velocity was 3km/s. According to the Barton relation (2006) the seepage potential in dam sit abutments, is low. A low velocity zone has been detected above the 690 m level in right abutment. It shows that the weak zones extended from surface down to this level. Despite the presence of some weak zones, the rock mass quality is good, and the design of the grout curtain could help to bypass the reservoir water away from these seepage paths

Keywords

References
Angioni, T., Rechtien, R. D. , Cardimono, S. J. & Luna, R., 2003- Crosshole seismic tomography and borehole logging for engineering site characterization in Sikeston, MO, USA, Tectonophysics, vol. 368, P.P.119 – 137.
Baan, M. V.& Jutten, J., 2000- Neural networks in geophysical applications, Geophysics, vol. 65, NO. 4, P.P. 1032–1047.
Bai, C. & Greenhalgh, S., 2005- 3-D Non-linear travel-time tomography: imaging high contrast velocity anomalies, Pure and Applied Geophysics, vol.162, P.P. 2029–2049.
Barton, N., 2006 - Rock quality, seismic velocity, attenuation and anisotropy, First Edition Taylor & Francis.
Berryman, J. G., 2000-  Analysis of approximate inverses in tomography:I. Resolution analysis of common inverses , Optimization and Engineering, vol. 1, 87–115.
Berryman, J. G., 1991- Lecture notes on nonlinear traveltime and tomography, Earth resources laboratory, Massachusetts Institute of Technology, University of California.
Bichkar, R. S., Singh, S. K. , Ray, A. K., 1998- Genetic algorithmic approach to the detection of subsurface voids in cross-hole seismic tomography  , Pattern Recognition Letters vol. 19, P.P. 527–536.
Boschetti, F. , Dentith, M. C. & List, R. D., 1996- Inversion of seismic refraction data using genetic algorithms  , Geophysics, vol. 61, NO. 6, p.p 1715–1727.
Dietler, Th. , Malekzadeh, L. , Binazadeh, K. H. & Novin, H., 2008- Bakhtiari dam and hydrolic power project ,Geological report, Iran Water and Power Resources Development Co (IWPC) Authority.
Gheshlaghi, F., 1997- Tomographic imaging in civil engineering infrastructure, PH.D. Thesis university of waterloo.
Golami, A., 2005- Nonlinear travel time tomography, Institute of geophysics university of  Tehran (in Persian).
Greenhalgh, S., Zhou, B. & Cao, S., 2003- Crosswell seismic experiment for nickel sulphide exploration,  Journal of Applied Geophysics 53, P.P. 77– 89.
Gu, H., Cai, C. & Wang, Y., 2006- Investigation of Fractures Using Seismic Computerized Crosshole Tomography, JEEG, vol. 11, Issue 2, P.P 143–150.
Hansen, T. M. , Journel, A. J. , Tarantola, A. & Mosegaard, K. , 2006- Linear inverse Gaussian theory and geostatistics,  Geophysics, vol. 71, NO. 6, P.P. R101–R111.
Hanson, D. R., Vandegrift,T. L. , Demarco, M. J. & Hanna, K., 2002- Advanced techniques in site characterization and mining hazard detection for the underground coal industry  , Int. J. Coal Geol., vol. 50, P.P. 275–301.
Hyndman, D. W. & Harris, J. M., 1996- Traveltime inversion for the geometry of aquifer lithologie  , Geophysics, Vol. 61, Issue 6, pp. 1728-1737.
Li, C., 2005- Seismic tomography with non-uniform ray coverage and autoregressive extrapolation, Ph.D. thesis, Purdue University,  213 pages; AAT 3185792.
Liu, J., 2005- Nonlinear seismic tomography and model uncertainty estimation with the Markov Chain Monte Carlo method , Ph.D. thesis, Purdue University, 161 pages; AAT 3210741.
Nicksiar, M. , Esfandiary, M., Mehinrad, A. & Binazadeh, K., 2007- Application of Seismic Tomography for detecting potential seepage paths in Bakhtyari dam,  Iran  , Int J Rock Mech Mining Sci,  vol. 44.
Santamarina, J. C. & Fratta, D., 2005- Discrete signals and inverse problems: An introduction for engineers and scientists, First Edition, Wiley.
Um, J. & Thurber, C., 1987- A fast algorithm for two-point seismic ray tracing  , Bull. Seismol. Soc. Am., vol. 77, P.P. 972-986.
Williams, M. C. , Leighton, V. L. , Vassiliou, A. A. , Tan, H. & Nemeth, T., 1997- Crosswell seismic imaging: A technology whose time has come?  , The Leading Edge, vol. 16, Issue 3, P.P. 285-291. 
Wong, J., 2000- Crosshole seismic imaging for sulfide orebody delineation near Sudbury, Ontario, Canada  , Geophysics, Vol. 65, Issue 6, pp. 1900-1907.