[CIG-SEISMO] Modelling seafloor roughness with SPECFEM3D

[Dimitri Komatitsch]

Hi Jean,

Thanks for your message. Alexis Bottero is currently doing this as well 
in his PhD thesis here, let me put you in contact with him and with my 
colleague Paul Cristini.

Best regards,
Dimitri.

On 07/05/2017 04:28 PM, Jean Lecoulant wrote:
> To whom it may concern,
> 
> I seek to model the emission of T-waves by a rough seafloor with SPECFEM3D.
> 
> To do this, I need to mesh a random topography on the crust/ocean 
> interface, with a topography wave-length an order of magnitude smaller 
> than the typical wave-length of T-waves. The wave-length of the T-waves 
> emitted by my seismic source is about 1 km, therefore I need a 
> topography with a 100 m wave-length. The discretization shall be done 
> with a space-step dx ~ 10 m to obtain a smooth topography.
> 
> The calculation domain for the simulations is a parallelepiped, 10x10 km 
> wide and 6 km thick. It is horizontally divided in a 3 km thick fluid 
> medium (the ocean) underlain by a 3 km thick solid medium (the Earth 
> crust). All sides, except the top (sea) surface, are absorbing layers. I 
> use Gmsh to build meshes and I run the appropriate python and fortran 
> routines to convert these meshes. I have been using different 
> discretization, varying the number of finite elements both along the 
> horizontal axes and along the vertical axis. In the horizontal plan, I 
> have tested 1001x1001 (dx = 10 m), 501x501 (dx = 25 m), 251x251 (dx = 40 
> m) and 201x201 (dx = 50 m) meshes. For each of these discretizations, I 
> have tested different numbers of finite elements along the vertical axis 
> in the crust and in the ocean: 31 (dz = 100m), 51 (dz = 60m) and 91 (dz 
> = 33.33m).
> 
> Running the SPECFEM3D routine xgenerate_databases with those meshes, I 
> encounter two different errors. When there are too few elements along 
> the vertical: 'there is an error in separation of beta_x, alpha_y, 
> alpha_z'. When there are too many elements along the vertical: 'Access 
> to an undefined portion of a memory object'. Hence I cannot find a 
> satisfying mesh.
> 
> Does anyone know a way to generate a mesh able to model a rough seafloor?
> 
> Best regards,
> 
> Jean Lecoulant
> Ph.D. student in geophysics
> Laboratoire Géosciences Océan
> Institut Universitaire Européen de la Mer
> Université de Bretagne Occidentale, France
> Tel: +33 (0)2 98 49 88 94
> 
> 
> 
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-- 
Dimitri Komatitsch, CNRS Research Director (DR CNRS)
Laboratory of Mechanics and Acoustics, Marseille, France
http://komatitsch.free.fr