Azimuthal anisotropy of the Sayan-Baikal fold region by the receiving functions of distant earthquakes

The purpose of the work is the determination of a detailed velocity structure of the earth's interior of the seismically active Sayan-Baikal fold region, including the identification of the azimuths and depths in the vicinity of the observation points with anisotropic properties. The source data for the study is the long-term observations by five broadband seismic stations in the Sayano-Baikal fold region. The proposed methodology for identifying the depths and directions of the earth's interior with anisotropic properties is based on the longitudinal receiving function method. The receiving functions for all possible directions of each observation point have been selected from the tele-seismic records. The azimuthal boundaries are identified in relation to the observing station where the receiving functions change significantly, which means a change in the velocity structure when crossing these conditional boundaries. Within the azimuth ranges (BAZ) with homogeneous receiving functions, velocity models (V_S) have been calculated by inverting the functions. The models take into account the relationship between the depth of medium sounding (h) and the corresponding distance from the seismic station (d). Based on the one-dimensional velocity sections for different azimuths, circular models V_S(h,BAZ,d) have been constructed with the account of the seismic drift. The models visualize the velocity structure in relation to all observation points at the depths up to 70 km and 270 km. As a result of the study, a set of models reflecting the detailed deep-seated velocity structure of the Sayano-Baikal folded region has been obtained. The velocities of the seismic waves V_S ( h ) have been determined within the earth's crust with an average depth step of 1 km, and within the mantle, with a step of 5-10 km. The circular models V_S(h,BAZ,d) clearly demonstrate the velocity heterogeneity in various directions from the observation point and allow one to identify the anisotropy of the medium. The latter is manifested as the presence of a symmetry axis in the circular models, which on average has a northwest-southeast orientation, but varies with the depth.

seismic anisotropy, Sayano-Baikal fold region, receiver function method, deep velocity sections, tele-seismic data

1. Forsyth DW. The early structural evolution and anisotropy of the oceanic upper mantle. Geophysical Journal of the Royal Astronomical Society. 1975;43(1):103–162. https://doi.org/10.1111/j.1365-246X.1975.tb00630.x

2. Trampert J, Woodhouse JH. Global anisotropic phase velocity maps for fundamental mode surface waves between 40 and 150 s. Geophysical Journal International. 2003;154(1):154–165. https://doi.org/10.1046/j.1365-246X.2003.01952.x

3. Dziewonski AM, Anderson DL. Preliminary reference Earth model. Physics of the Earth and Planetary Interiors. 1981;25(4)297–356. https://doi.org/10.1016/0031-9201(81)90046-7

4. Mitchell BJ. On the inversion of Loveand Rayleigh-wave dispersion and implications for the Earth structure and anisotropy. Geophysical Journal of the Royal Astronomical Society. 1984;76(1):233–241. https://doi.org/10.1111/j.1365-246X.1984.tb05040.x

5. Montagner J-P, Tanimoto T. Global upper mantle tomography of seismic velocities and anisotropies. Journal of Geophysical Research. 1991;96(B12):20337–20351. https://doi.org/10.1029/91JB01890

6. Villaseñor A, Ritzwoller MH, Levshin AL, Barmin MP, Engdahl ER, Spakman W, et al. Shear velocity structure of central Eurasia from inversion of surface wave velocities. Physics of the Earth and Planetary Interiors. 2001;123(2-4):169–184. https://doi.org/10.1016/S0031-9201(00)00208-9

7. Panning M, Romanowicz B. Inferences on flow at the base of the Earth’s mantle based on seismic anisotropy. Science. 2004;303(5656):351–353. https://doi.org/10.1126/science.1091524

8. Yanovskaya TB, Kozhevnikov VM. Upper mantle anisotropy beneath the Asian continent from group velocities of Rayleigh and Love waves. Geologiya i geofizika. 2006;47(5):622–629. (In Russ.)

9. Vinnik LP, Kosarev GL, Makeeva LI. Anisotropy by the observations of SKS and SKKS waves. Doklady Akademii nauk SSSR. 1984;278(6):1335–1339. (In Russ.)

10. Vinnik LP, Makeyeva LI, Milev A, Usenko AYu. Global patterns of azimuthal anisotropy and deformations in the continental mantle. Geophysical Journal International. 1992;111(3):433–447. https://doi.org/10.1111/j.1365-246X.1992.tb02102.x

11. Gol'din SV, Suvorov VD, Makarov PV, Stefanov YuP. An instability gravity model for the structure and stress-stain state of lithosphere in the Baikal rift. Geologiya i geofizika. 2006;47(10):1094–1105. (In Russ.)

12. Gao SS, Liu KH, Davis PM, Slack PD, Zorin YA, Mordvinova VV, et al. Evidence for smallscale mantle convection in the upper mantle beneath the Baikal rift zone. Journal of Geophysical Research: Solid Earth. 2003;108(B4):2194. https://doi.org/10.1029/2002JB002039

13. Gao SS, Liu KH, Chen C. Significant crustal thinning beneath the Baikal rift zone: new constraints from receiver function analysis. Geophysical Research Letters. 2004;31(20):L20610. https://doi.org/10.1029/2004GL020813

14. Barruol G, Deschamps A, Deverchere J, Mordvinova VV, Ulziibat M, Perrot J, et al. Upper mantle flow beneath and around the Hangay dome, Central Mongolia. Earth and Planetary Science Letters. 2008;274(1-2):221–233. http://dx.doi.org/10.1016/j.epsl.2008.07.027

15. Oreshin S, Vinnik L, Makeyeva L, Kosarev G, Kind R, Wentzel F. Combined analysis of SKS splitting and regional P traveltimes in Siberia. Geophysical Journal International. 2002;151(2):393–402. https://doi.org/10.1046/j.1365-246X.2002.01791.x

16. Calais E, Vergnolle M, San'kov V, Lukhnev A, Miroshnitchenko A, Amarjargal Sh, et al. GPS measurements of crustal deformation in the Baikal-Mongolia area (1994–2002): implications for current kinematics of Asia. Journal of Geophysical Research: Solid Earth. 2003;108(B10):2501. https://doi.org/10.1029/2002JB002373

17. Silver PG, Chan WW. Shear-wave splitting and subcontinental mantle deformation. Journal of Geophysical Research: Solid Earth.1991;96(B10):16429–16454. https://doi.org/10.1029/91JB00899

18. Gao S, Davis PM, Liu H, Slack PD, Zorin YuA, Mordvinova VV, et al. Seismic anisotropy and mantle flow beneath the Baikal rift zone. Nature. 1994;371(6493):149–151. https://doi.org/10.1038/371149a0

19. Gao S, Davis PM, Liu H, Slack PD, Rigor AW, Zorin YA, et al. SKS splitting beneath continental rift zones. Journal of Geophysical Research: Solid Earth. 1997;102(B10):22781–22797. https://doi.org/10.1029/97jb01858

20. Dricker IG, Roecker SW. Lateral heterogeneity in the upper mantle beneath the Tibetan plateau and its surroundings from SS-S travel time residuals. Journal of Geophysical Research: Solid Earth. 2002;107(B11):2305. https://doi.org/10.1029/2001JB000797

21. Vinnik LP. Detection of waves converted from P to SV in the mantle. Physics of the Earth and Planetary Interiors. 1977;15(1):39–45. https://doi.org/10.1016/0031-9201(77)90008-5

22. Kosarev GL, Makeyeva LI, Vinnik LP. Inversion of teleseismic P-wave particle motions for crustal structure in Fennoscandia. Physics of the Earth and Planetary Interiors. 1987;47:11–24. https://doi.org/10.1016/0031-9201(87)90063-X

23. Zorin YuA, Mordvinova VV, Turutanov EKh, Belichenko VG, Artemyev AA, Kosarev GL, et al. Low seismic velocity layers in the Earth’s crust beneath Eastern Siberia (Russia) and Central Mongolia: receiver function data and their possible geological implication. Tectonophysics. 2002. 2002;359(3-4):307–327. https://doi.org/10.1016/S0040-1951(02)00531-0

24. Stammler K. SeismicHandler – programmable multichannel data handler for interactive and automating processing of seismological analyses. Computers & Geosciences. 1993;19(2):135–140. https://doi.org/10.1016/0098-3004(93)90110-Q

25. Kosarev GL, Petersen NV, Vinnik LP, Roecker SW. Receiver functions for the Tien Shan analog broadband network: contrast in the evolution of structures across the Talasso-Fergana fault. Journal of Geophysical Research: Solid Earth. 1993;98(B3):4437–4448. https://doi.org/10.1029/92JB02651

26. Kind R, Kosarev GL, Petersen NV. Receiver functions at the stations of the German Regional Seismic Network (GRSN). Geophysical Journal International. 1995;121(1):191–202. https://doi.org/10.1111/j.1365-246X.1995.tb03520.x

27. Haskell NA. Crustal reflection of plane P and SV waves. Journal of Geophysical Research. 1962;67(12):4751–4768. https://doi.org/10.1029/JZ067i012p04751

28. Krylov SV, Mishen'kin BP, Mishen'kina ZR, Petrik GV, Sergeev VN, Shelud'ko IF, et al. Detailed seismic studies of the lithosphere at the P and S waves. Novosibirsk: Nauka; 1993. 199 p. (In Russ.)

29. Lobkovskii LI. Geodynamics of spreading and subduction zones, and bunk plate tectonics. Moscow: Nauka; 1988. 251 p. (In Russ.)

30. Kennett BLN, Engdahl ER. Traveltimes for global earthquake location and phase identification. Geophysical Journal International. 1991;105(2):429–465. https://doi.org/10.1111/j.1365-246X.1991.tb06724.x