Crustal seismic anisotropy in the south-central Alborz region using Moho Ps converted phases

Document Type : Research

Authors

1 Institute of Geophysics, University of Tehran, P.O. Box 14155- 6466, Tehran, Iran

2 International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran

Abstract

In this paper to find stable anisotropy direction with minimum error, we attempt to automate the choice of analysis of Moho Ps phase window by performing a grid search over different windows. We have determined the anisotropy direction in the crust of the Alborz region by using 8 events recorded at three IIEES seismic broadband stations (i. e. DAMV, THKV and CHTH).
Analysis of shear wave splitting of the Ps conversion from the crust-mantle boundary indicates a fast azimuth of anisotropy oriented approximately NE-SW. This strongly suggests coherent crustal anisotropy with a fast direction perpendicular to the strike of mountain block ranges.
We estimate the average directions of anisotropy under three stations, DAMV, THKV and CHTH of 42, 55, 55 degree, respectively. Moreover our results show that the magnitude of anisotropy are 0.23, 0.22, 0.27 seconds, respectively, which are in good agreement with the geology and tectonic setting of this region.

Keywords


Ague, J. J., 1995, Deep crustal growth of Quartz, kyanite and garnet into large aperture, fluid-filled fractures, northeastern Connecticut, USA, J. Metamorph. Geol., 13, 299-314.
Allen M. B., Ghassemi, M. R., Sharabi, M., and Qorashi, M., 2003, Accommodation of late Cenozoic oblique shortening in the Alborz range, Iran, J. Struct. Geol., 25, 659-672.
Ammon, C. J., 1991, The isolation of receiver effects from teleseismic P waveforms. B. Seismol. Soc. Am., 81, 2504-2510.
Asudeh, I., 1982, Seismic structure of Iran from surface and body wave data. Geophys. J. Roy. Astron. Soc., 71, 715-730.
Babuska, V., and Cara, M., 1991, Seismic Anisotropy in the Earth (Kluwer Academic, Dordrecht.
Babuska, V., and Pros, Z., 1984, Velocity anisotropy in granodiorite and quartzite due to the distribution of microcracks, Geophys. J. Roy. Astron. Soc., 76, 121-127.
Backus, G. E., 1962, Long-wave elastic anisotropy produced by horizontal layering, J. Geophys. Res., 67, 4427-4440.
Bowman, J. R., and Ando, M., 1987, Shear-wave splining in the upper-mantle wedge above the Tonga subduction zone, Ceophys. J. Roy. Astron. Soc., 88, 25-41.
Burdick, L. J., and Langston, C. A., 1977, Modeling crustal structure through the use of converted phases in teleseismic body waveforms, B. Seismol. Soc. Am., 67, 677-691.
Chen, C. Y., Chen, W. P., and Molnar, P., 1980, The uppermost mantle P wave velocities beneath Turkey and Iran. Geophys. Res. Lett., 7, 77-80.
Crampin, S., 1984a, An introduction to wave propagation in anisotropic media, ceophys. J. Roy. Astron. Soc., 76, 17-28.
Crampin, S., 1984b, Effective anisotropic elastic constants for wave propagation through cracked solids, Ceophys. J. Roy. Astron. Soc., 76, 135-145.
Crampin, S., 1991, Effects of point singularities on shear-wave propagation in sedimentary basins, Geophys. J. Int. 107, 531-543.
Crampin, S., Chesnokov, E. M., and Hipkin, R. G., 1984a, Seismic anisotropy-The state of the art; II, Ceophys. J. Roy. Astron. Soc., 76, 1-16.
Crampin, S., Evans, R., and Atkinson, B. K., 1984b, Earthquake prediction: A new physical basis, Ceophys. J. Roy. Astron. Soc., 76, 147-156.
Dehghani, G. A., and Makris, J., 1984, The gravity field and crustal structure of Iran. Neues Jahrb. Geol. Palaeontol., 168, 215-229.
De Martini, P. M., Hessami, K., Pantosti, D., D'Addezio, G., Alinaghi, H., and Gafory-ashtiani, H., 1998, A geological contribution to the evaluation of the seismic potential of the Kahrizak fault (Tehran, Iran). Tectonophysics. 287, 187-199.
DeMets, C., Gordon, R. G., Argus, D. F., and Stein, S., 1990, Current plate motions, Geophys. J. Int., 101, 425-478.
Doloei, J., and Roberts, R., 2003, Crust and uppermost mantle structure of Tehran region from analysis of teleseismic P-waveform receiver functions, Tectonophysics. 364, 115-133.
Fouch, M. J., Fischer, K. M., Parmentier, E. M., Wysession, M. E., and Clarke, T. J., 2000, Shear wave splitting, continental keels, and patterns of mantle flow. J. Geophys. Res., 105(B3), 6255-6275.
Fouch, M. J., and Rondenay, S., 2005, Continental Seismic Anisotropy, Submitted to Phys. Earth Planet Int August 2005.
Hearn, T. M., 1996, Anisotropic Pn tomography in the western United States, J. Geophys. Res., 101, 8403-8414.
Hudson, J. A., 1981, Wave speeds and attenuation of elastic waves in material containing cracks,  Geophys. J. Roy. Astron. Soc., 64, 133-150.
Jackson J. A., and McKenzie, D. P., 1984, Active tectonics of the Alpine-Himalayan Belt between western Turkey and Pakistan, Geophys. J. Roy. Astron. Soc., 77, 185-246.
Jackson J., Priestley, K., Allen, M., and Berberian, M., 2002, Active tectonics of the South Caspian Basin, Geophys. J. Int., 148, 214-245.
Kosarev, G. L., Makeyeva, L. I., and Vinnik, L. P., 1984, Anisotropy of the mantle inferred from observations of P to S converted waves, Ceophys. J. Roy. Astron. Soc., 76, 209-220.
Langston, C. A., 1977, The effect of planar dipping structure on source and receiver responses for constant ray parameter, B. Seismol. Soc. Am., 67, 1029-1050.
Langston, C. A., 1979, Structure under Mount Rainier, Washington, inferred from teleseismic body waves, J. Ceophys. Res., 84, 4749-4762.
Levin, V., Menke, V., and Park, J., 1999, Shear wave splitting in the Appalachians and the Urals: A case for multilayered anisotropy, J. Geophys. Res., 104(B8): 17, 975-993.
Lynn, H. B., 1991, Field measurements of azimuthal anisotropy: first 60 meters, San Francisco Bay Area, CA, and estimation of the horizontal stress ratio from VS1/ VS2, Geophysics. 56, 822-832.
Mangino S. and K. Priestley (1998), The crustal structure of the southern Caspian region, Geophys. J. Int., 133, 630-648.
McQuarrie N., Stock, J. M., Verdel, V., and Wernicke, B. P., 2003, Cenozoic evolution of Neotethys and implications for the causes of plate motions, Geophys. Res. Lett. 30 (doi:10.1029/2003GL017992).
Owens, T. J., 1987, Crustal structure of the Adirondack mountains determined from broadband teleseismic waveform modeling, J. Ceophys. Res., 92, 6391-6401.
Owens, T. J., Zandt, G., and Taylor, S. R., 1984, Seismic evidence for an ancient rift beneath the Cumberland Plateau, Tennessee: A detailed analysis of broadband teleseismic P waveforms, J. Ceophys. Res., 89, 7783-7795.
Park, J., and Levin, V., 2002, Seismic anisotropy: Tracing plate dynamics in the mantle. Science, 296(5567), 485-489.
Phinney, R. A., 1964, Structure of the Earth's crust from spectral behavior of long-period body waves, J. Ceophys. Res., 69, 2997-3017.
Raitt, R. W., Shor Jr., G. G., Francis, T. J. G., and Morris, G. B. 1969, Anisotropy of the Pacific Upper Mantle, J. Geophys. Res., 74, 3095-3109.
Ribe, N., 1992, On the Relation Between Seismic Anisotropy and Finite Strain, J. Geophys. Res., 97, 8737-8747.
Savage, M. K., Silver, P. G., and Meyer, R. P., 1990, Observations of teleseismic shear-wave splitting in the Basin and Range from portable and permanent stations, Geophys. Res. Lett., 17(1), 21-24.
Shearer, P. M., and Orcutt, J. A., 1986, Compressional and shear wave anisotropy in the oceanic lithosphere-The Ngendei seismic refraction experiment. Geophys. J. Roy. Astron. Soc., 87, 967-1003.
Silver, P. G., 1996, Seismic anisotropy beneath the continents: probing the depths of Geology, Ann. Rev. Earth Planet. Sci., 24, 385-432.
Si1ver, P. G., and Chan, W. W., 1988, Implications for continental structure and evolution from seismic anisotropy, Nature, 335, 34-39.
Silver, P.G., and Chan, W. W., 1991, Shear wave splitting and subcontinental mantle deformation, J. Geophys. Res., 96(B10): 16, 429-454.
Sobouti, F., and Arkani-Hamed, J., 1996, Numerical modelling of the deformation of the Iranian plateau. Geophys. J. Int. 126, 805-818.
Sodoudi, F., Kind, R., Kamalian, N., and Sadidkhoy, A., 2004, The crust and upper mantle structure of the central Alborz  (Iran) using teleseismic receiver function, EGU meeting 2004, Nice, France.
Teanby, N. A., Kendall, J-M., and van der Baan, M., 2004, Automation of shear wave splitting measurements using cluster analysis, B. Seismol. Soc. Am., 94, 453-463.
Vernant Ph., Nilforoushan, F., Che´ry, F., Bayer, R., Djamour, Y., Masson, F., Nankali, H., Ritz, J. F., Sedighi, M., and Tavakoli, F., 2004, Deciphering oblique shortening of central Alborz in Iran using geodetic data, Earth Planet. Sci. Lett. 223, 177-185.
Vinnik, L. P., Farra, V., and Romanowicz, B., 1989, Azimuthal anisotropy in the Earth from observations of SKS at GEOSCOPE and NARS broadband stations, B. Seismol. Soc. Am., 79(5), 1542-1558.
Vinnik, L. P., Makeyeva, L. I., Milev, A., and Usenko, A. Y., 1992, Global patterns of azimuthal anisotropy and deformations in the continental mantle, Geophys. J. Int. 111, 433-447.
Zhang, S. and Karato, S., 1995, Lattice Preferred Orientation of olivine aggregates deformed in simple shear, Nature. 375, 774-777.
Zhi, Z., and Schwartz, S. Y., 1994, Seismic anisotropy in the shallow crust of the Loma Prieta Segment of the San Andreas fault system, J. Geophys, Res., 99, 9651-9661.