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is one of the Thomsen anisotropic parameters (q.v.):

where cij indicate elements in the elastic constants matrix [1]. Another Thomsen anisotropic parameter is , and with weak anisotropy, , which is independent of , is generally used instead of it is the most critical factor for transverse isotropy[2]:

Several seismic expressions involve , such as the short-offset moveout correction to the vertical velocity,

For long offsets, another anisotropy parameter, (eta) captures the deviation of long-offset P-wave moveout from what it would have been for isotropicity [3]:


  1. Thomsen, Leon (1986). "Weak elastic anisotropy". GEOPHYSICS 51 (10): 1954–1966. doi:10.1190/1.1442051. PDF version.
  2. Thomsen, Leon (2002). Understanding Seismic Anisotropy in Exploration and Exploitation. Society of Exploration Geophysicists. doi:10.1190/1.9781560801986.
  3. Alkhalifah, Tariq; Tsvankin, Ilya (1995). "Velocity analysis for transversely isotropic media". GEOPHYSICS 60 (5): 1550–1566. doi:10.1190/1.1443888.PDF version.