How robust is isotropic delay time tomography for anisotropic mantle?

Using isotropic inversion of teleseismic P‐travel times computed for laterally varying anisotropic structures, we investigate how anisotropy may show up in classical tomographic studies based on isotropic 3‐D inversions. Anisotropic bodies of several tens of kilometers in the upper mantle may significantly bias the estimation of the isotropic part of a P‐wave velocity image. The largest artifacts are introduced by anisotropic bodies with a dipping olivine “a” axis which could be associated with fossil subduction zones. However, anisotropy‐induced artifacts are negligible for anisotropy caused by pure shear deformation of the lithosphere due to horizontal extension or compression. The negative P‐wave velocity anomaly arising from isotropic inversion beneath a rift zone may be enhanced if the olivine crystal's “a” axes are preferentially oriented parallel to the asthenospheric flow along the rift axis. Examination of recently published tomographic models shows that the image of the Rhine Graben may contain significant anisotropic artifacts.

[1]  J. Montagner.  Where Can Seismic Anisotropy Be Detected in the Earth’s Mantle? In Boundary Layers... , 1998 .

[2]  K. Fuchs,et al.  Upper mantle temperatures and lithosphere-asthenosphere system beneath the French Massif Central constrained by seismic, gravity, petrologic and thermal observations , 1997 .

[3]  P. Davis,et al.  The upper mantle structure of the central Rio Grande rift region from teleseismic P and S wave travel time delays and attenuation , 1996 .

[4]  M. Cara,et al.  ANISOTROPY AND P-WAVE TOMOGRAPHY : A NEW APPROACH FOR INVERTING TELESEISMIC DATA FROM A DENSE ARRAY OF STATIONS , 1996 .

[5]  P. Silver.  SEISMIC ANISOTROPY BENEATH THE CONTINENTS: Probing the Depths of Geology , 1996 .

[6]  M. Wilson,et al.  Imaging a mantle plume beneath the French Massif Central , 1995 .

[7]  M. Granet,et al.  A tomographic study of the lithosphere beneath the Pyrenees from local and teleseismic data , 1995 .

[8]  U. Achauer.  NEW IDEAS ON THE KENYA RIFT BASED ON THE INVERSION OF THE COMBINED DATASET OF THE 1985 AND 1989/90 SEISMIC TOMOGRAPHY EXPERIMENTS , 1994 .

[9]  J. Plomerová,et al.  Models of seismic anisotropy in the deep continental lithosphere , 1993 .

[10]  P. Silver,et al.  Interpretation of SKS-waves using samples from the subcontinental lithosphere , 1993 .

[11]  A. Nicolas.  Why fast polarization directions of SKS seismic waves are parallel to mountain belts , 1993 .

[12]  M. Granet,et al.  Southern Rhine Graben: small-wavelength tomographic study and implications for the dynamic evolution of the graben , 1993 .

[13]  A. Milev,et al.  Global patterns of azimuthal anisotropy and deformations in the continental mantle , 1992 .

[14]  Neil M. Ribe,et al.  On the relation between seismic anisotropy and finite strain , 1992 .

[15]  D. G. Isaak.  High‐temperature elasticity of iron‐bearing olivines , 1992 .

[16]  K. Fuchs.  Recently formed elastic anisotropy and petrological models for the continental subcrustal lithosphere in southern Germany , 1983 .

[17]  D. L. Anderson,et al.  Upper mantle anisotropy - Evidence from free oscillations , 1982 .

[18]  D. McKenzie,et al.  Finite deformation during fluid flow , 1979 .

[19]  Keiiti Aki,et al.  Determination of the three‐dimensional seismic structure of the lithosphere , 1977 .

[20]  U. Christensen,et al.  Temperature and Dynamics of the Upper Mantle Beneath the French Massif Central , 1997 .

[21]  J. R. Evans,et al.  Teleseismic velocity tomography using the ACH method: theory and application to continental-scale studies , 1993 .

[22]  Ș.,et al.  Seismic Velocities in Mantle Minerals and the Mineralogy of the Upper Mantle , 2022 .