[CIG-SEISMO] PREM crust in SPECFEM3D GLOBE

[A. Datta]

Hi there,

I have a question about the implementation of the PREM crust in 
SPECFEM3D_GLOBE. As I understand, in PREM the top 3 km of the earth (and 
the crust) correspond to a water layer with rho = 1.02, Vp = 1.45 and Vs = 
0

But in SPECFEM, this is not the case. The PREM crust appears to uniform 
between 0 and 15 km. Here's an extract from the model_prem routine:

else if(r > RMIDDLE_CRUST .and. r <= ROCEAN) then
      rho=2.6d0
      vpv=5.8d0
      vsv=3.2d0
      vph=vpv
      vsh=vsv
      Qmu=600.0d0
      Qkappa=57827.0d0
else if(r > ROCEAN) then
      rho=2.6d0
      vpv=5.8d0
      vsv=3.2d0
      vph=vpv
      vsh=vsv
      Qmu=600.0d0
      Qkappa=57827.0d0

RMIDDLE_CRUST corresponds to a depth of 15km and ROCEAN, to 3km. Even 
though depths above and below 3 km are considered in two separate if 
blocks, the model values assigned, as you can see, are the same. An unusual 
bit of code.

I just wanted to confirm the crust in PREM as implemented in 
SPECFEM3D_GLOBE is indeed different from the actual PREM crust, and if so, 
it would be great to know why.

Thank you very much,

Arjun Datta

-- 
PhD candidate (Geophysics)
Bullard Laboratories
University of Cambridge
Ph: +44-1223-748938