[CIG-SEISMO] Modelling seafloor roughness with SPECFEM3D

[Jean Lecoulant]

  Bonjour,

Merci beaucoup pour votre réponse et pour m'avoir donner les adresses
d'Alexis Bottero et de Paul Cristini. Ils pourront sûrement résoudre ce
problème.

Cordialement,

Jean

Dimitri Komatitsch <komatitsch at lma.cnrs-mrs.fr> a écrit :

> 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,
> Francehttp://komatitsch.free.fr
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