Custom model with smoothly varying velocities

[kerim371]

Hi,

I'm just starting using SPECFEM2D.

It is not clear to me how to build model when its velocities change smoothly.
As I understand I can set different values to MODEL:

# available models
#   default       - define model using nbmodels below
#   ascii         - read model from ascii database file
#   binary        - read model from binary databse file
#   binary_voigt  - read Voigt model from binary database file
#   external      - define model using define_external_model subroutine
#   gll           - read GLL model from binary database file
#   legacy        - read model from model_velocity.dat_input
MODEL                           = legacy

Ok, I can try binary format and use some files with naming like DATA/proc***_rho.bin, DATA/proc***_vp.bin, DATA/proc***_vs.bin.
But then it seems I have to define materials for all points because there is no "layers" and every point has its own velocity value:

# material properties
# number of model materials
nbmodels                        = 1
# available material types (see user manual for more information)
#   acoustic:              model_number 1 rho Vp 0  0 0 QKappa 9999 0 0 0 0 0 0 (for QKappa use 9999 to ignore it)
#   elastic:               model_number 1 rho Vp Vs 0 0 QKappa Qmu  0 0 0 0 0 0 (for QKappa and Qmu use 9999 to ignore them)
#   anisotropic:           model_number 2 rho c11 c13 c15 c33 c35 c55 c12 c23 c25   0 QKappa Qmu
#   anisotropic in AXISYM: model_number 2 rho c11 c13 c15 c33 c35 c55 c12 c23 c25 c22 QKappa Qmu
#   poroelastic:           model_number 3 rhos rhof phi c kxx kxz kzz Ks Kf Kfr etaf mufr Qmu
#   electromagnetic:       model_number 4 mu0 e0 e11(e0) e33(e0) sig11 sig33 Qe11 Qe33 Qs11 Qs33 0 0 0
#   tomo:                  model_number -1 0 0 A 0 0 0 0 0 0 0 0 0 0

Is there a way to avoid setting velocities for the different materials in case I use some smoothly variang velocity model?

Appreciate any help.