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International Journal of Earth Sciences

, Volume 105, Issue 6, pp 1681–1692 | Cite as

Seismic anisotropy of the lithosphere/asthenosphere system beneath the Rwenzori region of the Albertine Rift

  • B. Homuth
  • U. Löbl
  • A. G. Batte
  • K. Link
  • C. M. Kasereka
  • G. Rümpker
Original Paper

Abstract

Shear-wave splitting measurements from local and teleseismic earthquakes are used to investigate the seismic anisotropy in the upper mantle beneath the Rwenzori region of the East African Rift system. At most stations, shear-wave splitting parameters obtained from individual earthquakes exhibit only minor variations with backazimuth. We therefore employ a joint inversion of SKS waveforms to derive hypothetical one-layer parameters. The corresponding fast polarizations are generally rift parallel and the average delay time is about 1 s. Shear phases from local events within the crust are characterized by an average delay time of 0.04 s. Delay times from local mantle earthquakes are in the range of 0.2 s. This observation suggests that the dominant source region for seismic anisotropy beneath the rift is located within the mantle. We use finite-frequency waveform modeling to test different models of anisotropy within the lithosphere/asthenosphere system of the rift. The results show that the rift-parallel fast polarizations are consistent with horizontal transverse isotropy (HTI anisotropy) caused by rift-parallel magmatic intrusions or lenses located within the lithospheric mantle—as it would be expected during the early stages of continental rifting. Furthermore, the short-scale spatial variations in the fast polarizations observed in the southern part of the study area can be explained by effects due to sedimentary basins of low isotropic velocity in combination with a shift in the orientation of anisotropic fabrics in the upper mantle. A uniform anisotropic layer in relation to large-scale asthenospheric mantle flow is less consistent with the observed splitting parameters.

Keywords

East African Rift system Albertine Rift Seismic anisotropy Shear-wave splitting Joint splitting analysis Waveform modeling 

Notes

Acknowledgments

Funding for this study was provided by the Deutsche Forschungsgemeinschaft (DFG). We thank the Geophysical Instrumentation Pool Potsdam (GIPP) for providing the seismological equipment and GEOFON for archiving the data. The support of the Ugandan National Council for Science and Technology and of the Ugandan Wildlife Authority is greatly appreciated. Data from station MBAR has been provided by GSN-IRIS/IDA. The manuscript significantly benefited from the constructive comments and suggestions of Tuna Eken and one anonymous reviewer.

Supplementary material

531_2014_1047_MOESM1_ESM.pdf (447 kb)
Supplementary material 1 (PDF 447 kb)

References

  1. Backus GE (1962) Long-wave elastic anisotropy produced by horizontal layering. J Geophys Res 67:4427–4440CrossRefGoogle Scholar
  2. Bagley B, Nyblade AA (2013) Seismic anisotropy in eastern Africa, mantle flow, and the African superplume. Geophys Res Lett 40:1500–1501. doi: 10.1002/grl.50315 CrossRefGoogle Scholar
  3. Batte AG, Rümpker G, Lindenfeld M, Schumann A (2014) Structurally controlled seismic anisotropy above small earthquakes in crustal rocks beneath the Rwenzori region, Albertine Rift, Uganda. J Afr Earth Sci (submitted)Google Scholar
  4. Ben Ismail W, Mainprice D (1998) An olivine fabric database: an overview of upper mantle fabrics and seismic anisotropy. Tectonophysics 296:145–158CrossRefGoogle Scholar
  5. Bendick R, McClusky S, Bilham R, Asfaw L, Klemperer S (2006) Distributed Nubia–Somalia relative motion and dike intrusion in the main Ethiopian rift. Geophys J Int 165:303–310CrossRefGoogle Scholar
  6. Bosworth W, Strecker MR, Bliniuk PM (1992) Integration of East African paleostress and present-day stress data: implications for continental stress field dynamics. J Geophys Res 97:11851–11865CrossRefGoogle Scholar
  7. Chorowicz J (2005) The East African Rift system. J Afr Earth Sci 43:379–410CrossRefGoogle Scholar
  8. Crampin S (1991) Wave propagation through fluid-filled inclusions of various shapes: interpretation of extensive-dilatancy anisotropy. Geophys J Int 104:611–623CrossRefGoogle Scholar
  9. Ebinger CJ (1989) Tectonic development and the western branch of the East African rift system. Geol Soc Am Bull 101:885–903CrossRefGoogle Scholar
  10. Foley SF (1992) Vein-plus-wall-rock melting mechanisms in the lithosphere and the origin of potassic alkaline magmas. Lithos 28:435–453CrossRefGoogle Scholar
  11. Foley SF, Link K, Tiberindwa JV, Barifaijo E (2012) Patterns and origin of igneous activity around the Tanzanian craton. J Afr Earth Sci 62:1–18CrossRefGoogle Scholar
  12. Fouch MJ, Rondenay S (2006) Continental seismic anisotropy. Phys Earth planet Int 158:292–320CrossRefGoogle Scholar
  13. Gao SS, Davis PM, Liu H, Slack PD, Rigor AW, Zorin YZ, Mordvinova VV, Kozhevnikov VM, Meyer RP (1994) Seismic anisotropy and mantle flow beneath the Baikal rift zone. Lett Nat 371:149–151CrossRefGoogle Scholar
  14. Gao SS, Davis PM, Liu H, Slack PD, Rigor AW, Zorin YZ, Mordvinova VV, Kozhevnikov VM, Logatchev NA (1997) SKS splitting beneath the continental rift zones. J Geophys Res 102:22781–22797CrossRefGoogle Scholar
  15. Gao SS, Liu KH, Abdelsalam MG (2010) Seismic anisotropy beneath the Afar depression and adjacent areas: implications for mantle flow. J Geophys Res 115. doi: 10.1029/2009JB007141
  16. Gummert M, Lindenfeld M, Wölbern I, Rümpker G, Kasereka CM, Batte AG (2014) Crustal structure and high-resolution Moho topography across the Rwenzori region (Albertine rift) from P-receiver functions. Submitted to Geological Society, London, Special PublicationsGoogle Scholar
  17. Hammond JOS, Kendall JM, Angus D, Wookey J (2010) Interpreting spatial variations in anisotropy: insights into the main Ethiopian rift from SKS waveform modeling. Geophys J Int 181:1701–1712Google Scholar
  18. Heintz M, Kennett BLN (2005) Continental scale shear-wave splitting analysis: investigation of seismic anisotropy underneath the Australian continent. Earth Planet Sci Lett 236:106–119CrossRefGoogle Scholar
  19. Holtzman BK, Kendall JM (2010) Organized melt, seismic anisotropy, and plate boundary lubrication. Geochem Geophys Geosyst 11:Q0AB06. doi: 10.1029/2010GC003296 CrossRefGoogle Scholar
  20. Ikelle LT, Amundsen L (2005) Introduction to petroleum seismology. Society of Exploration Geophysicists, TulsaCrossRefGoogle Scholar
  21. Karato SI (2003) The dynamic structure of the deep Earth: an interdisciplinary approach. Princeton University Press, PrincetonGoogle Scholar
  22. Kendall JM (1994) Teleseismic arrivals at a mid-ocean ridge: effects of mantle melt and anisotropy. Geophys Res Lett 21:301–304CrossRefGoogle Scholar
  23. Kendall JM, Stuart GW, Ebinger CJ, Bastow ID, Keir D (2005) Magma assisted rifting in Ethiopia. Nature 433:146–148CrossRefGoogle Scholar
  24. Kumazawa M, Anderson OL (1969) Elastic moduli, pressure derivatives, and temperature derivatives of single-crystal olivine and single-crystal forsterite. J Geophys Res 74:5961–5972CrossRefGoogle Scholar
  25. Lindenfeld M, Rümpker G (2011) Detection of mantle earthquakes beneath the East African rift. Geophys J Int 186:1–5CrossRefGoogle Scholar
  26. Lindenfeld M, Rümpker G, Batte A, Schumann A (2012) Seismicity at the Rwenzori Mountains, East African rift: earthquake distribution, magnitudes and source mechanisms. Solid Earth 3:251–264CrossRefGoogle Scholar
  27. Link K, Koehn D, Barth MG, Tiberindwa JV, Barifaijo E, Aanyu K, Foley SF (2010) Continuous cratonic crust between the Congo and Tanzania blocks in western Uganda. Int J Earth Sci 99(7):1559–1573. doi: 10.1007/s00531-010-0548-8 (Special Issue “Long-term Rift Evolution”)CrossRefGoogle Scholar
  28. Long MD, Silver PG (2009) Shear wave splitting and mantle anisotropy: measurements, interpretations, and new directions. Surv Geophys 30:407–461CrossRefGoogle Scholar
  29. Nicolas A, Christensen NI (1987) Formation of anisotropy in upper mantle peridotites: a review, in composition, structure, and dynamics of the lithosphere–asthenosphere system. Geodyn Ser 16, Fuchs K and Froidevaux C (ed), AGU, Washington, DC, pp 111–123Google Scholar
  30. Nicolas A, Achauer U, Daignieres M (1994) Rift initiation by lithospheric rupture. Earth Planet Sci Lett 123:281–298CrossRefGoogle Scholar
  31. Nyblade AA, Brazier RA (2002) Precambrian lithosphere controls on the development of the East African rift system. Geology 30:755–758CrossRefGoogle Scholar
  32. Rosenthal A, Foley SF, Pearson DG, Nowell GM, Tappe S (2009) Petrogenesis of strongly alkaline primitive volcanic rocks at the propagating tip of the western branch of the East African rift. Earth Planet Sci Lett 284:236–248CrossRefGoogle Scholar
  33. Rümpker G, Ryberg T (2000) New “Fresnel-zone” estimates for shear-wave splitting observations from finite-difference modeling. Geophys Res Lett 27:2005–2008CrossRefGoogle Scholar
  34. Rümpker G, Silver PG (1998) Apparent shear-wave splitting parameters in the presence of vertically varying anisotropy. Geophys J Int 135:790–800CrossRefGoogle Scholar
  35. Ryberg T, Rümpker G, Tittgemeyer M, Wenzel F (2002) Finite-difference simulations of seismic wavefields in isotropic and anisotropic Earth models. In: Krause E, Jäger W (eds) High performance computing in science and engineering 2001. Springer, Berlin, pp 35–47Google Scholar
  36. Sander S, Rosendhal BR (1989) The geometry of rifting in Lake Tanganyika, East Africa. J Afr Earth Sci 8:323–354CrossRefGoogle Scholar
  37. Savage MK (1999) Seismic anisotropy and mantle deformation: what have we learned from shear wave splitting? Rev Geophys 37:65–106CrossRefGoogle Scholar
  38. Silver PG (1996) Seismic anisotropy beneath the continents: probing the depths of geology. Annu Rev Earth Planet Sci 24:385–432CrossRefGoogle Scholar
  39. Silver PG, Chan WW (1991) Shear-wave splitting and subcontinental mantle deformation. J Geophys Res 96:16429–16454CrossRefGoogle Scholar
  40. Stamps DS, Calais E, Saria E, Hartnady CH, Nocquet JM, Ebinger CJ, Fernandes RM (2008) A kinematic model for the East African rift. Geophys Res Lett 35:L05304. doi: 10.1029/2007GL032781 CrossRefGoogle Scholar
  41. Tommasi A (1998) Forward modeling of the development of seismic anisotropy in the upper mantle. Earth Planet Sci Lett 160:1–13CrossRefGoogle Scholar
  42. Vauchez A, Tommasi A, Barroul G, Mamus J (2000) Upper mantle deformation and seismic anisotropy in continental rifts. Phys Chem Earth A 25(2):111–117CrossRefGoogle Scholar
  43. Walker KT, Nyblade AA, Klemperer SL, Bokelmann GHR, Owens TJ (2004) On the relationship between extension and anisotropy: constraints from shear-wave splitting across the East African Plateau. J Geophys Res 109. doi: 10.1029/2003JB002866
  44. Wallner H, Schmeling H (2010) Rift induced delamination of mantle lithosphere and crustal uplift: a new mechanism for explaining Rwenzori Mountains extreme elevation? Int J Earth Sci doi: 10.1007/s00531-010-0521-6
  45. Wölbern I, Rümpker G, Link K, Sodoudi F (2012) Melt infiltration of the lower lithosphere beneath the Tanzania craton and the Albertine rift inferred from S receiver functions. Geochem Geophys Geosyst 13(1). doi: 10.1029/2012GC004167
  46. Wölbern I, Löbl U, Rümpker G (2014) Crustal origin of trench-parallel shear-wave fast polarizations in the Central Andes. Earth Planet Sci Lett 392:230–238. doi: 10.1016/j.epsl.2014.02.032 CrossRefGoogle Scholar
  47. Wolfe CJ, Silver PG (1998) Seismic anisotropy of oceanic upper mantle: shear-wave splitting methodologies and observations. J Geophys Res 103:749–771CrossRefGoogle Scholar
  48. Zhang S, Karato SI (1995) Lattice preferred orientation of olivine aggregates deformed in simple shear. Nature 375:774–777. doi: 10.1038/375774a0 CrossRefGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  • B. Homuth
    • 1
  • U. Löbl
    • 1
  • A. G. Batte
    • 2
  • K. Link
    • 3
    • 4
  • C. M. Kasereka
    • 5
  • G. Rümpker
    • 1
  1. 1.Institute of GeosciencesGoethe University FrankfurtFrankfurt am MainGermany
  2. 2.Geology DepartmentMakerere UniversityKampalaUganda
  3. 3.Institute for GeosciencesJohannes Gutenberg University MainzMainzGermany
  4. 4.Gubelin Gem Lab Ltd.LuzernSwitzerland
  5. 5.Goma Volcano ObservatoryGomaDemocratic Republic of Congo

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