MS_VTI2

MS_VTI2 - generate elastic constants for a vertically transverse isotropic
            medium from xi, phi, eta parameters. Symmetry is in the 3-axis.

[C]=MS_VTI2(vp,vs,rh,xi,phi,eta)

Inputs:
    rh  : Density (kg/m2)
    vp  : km/s (isotropic average)
    vs  : km/s (isotropic average)
    xi, phi, eta : Dimensionless anisotropy parameters

Output:
     C : Stiffness tensor (6x6 notation, GPa)

Calculates the elastic tensor for a hexagonal (aka VTI) medium from
average Vp and Vs, and anisotropic parameters xi, phi and eta.

See, for example, Panning and Romanowicz (2006) for a definition of the
parameters.

Note: this is wrapper for MS_TI, provided for back-compatibility. **

References:
  Mark Panning and Barbara Romanowicz (2006) A three-dimensional radially
     anisotropic model of shear velocity in the whole mantle. Geophysical
     Journal International v167, 361–379.
     doi: 10.1111/j.1365-246X.2006.03100.x

See also: MS_TI, MS_VTI, MS_iso, MS_elasticDB