[CIG-SEISMO] Specfem3d globe: with an altered crustal model

[Kendall, Elodie]

Hi there,


I have created a new crust 2.0 (the same format but with crustal thickness perturbations added to each grid) and I want to analyse the effect on the synthetics. I have changed the maximum moho depth from 90 to 115 (the new max.), the mesher runs fine but the solver fails with error "forward simulation became unstable in fluid and blew up". I have suppressed the moho stretching and the solver runs without errors however I then lose accuracy as the moho is not being honoured.


Do you know how I could check how many GLL points sample each crustal point please? I assume that if it really undersampled (1 not 5 GLL for the oceans) I should use something like this to create a new mesh?

https://github.com/geodynamics/specfem3d/wiki/03_mesh_generation


Thanks a lot,
Elodie

________________________________
From: Ebru Bozdag <bozdag at mines.edu>
Sent: 19 July 2017 16:47
To: Kendall, Elodie
Subject: Re: [CIG-SEISMO] Specfem with an altered crustal model

Hi Elodie,

This was to diagnose where the problem was coming from. Just note that when you set SUPPRESS_MOHO_STRETCHING = .true. you are losing accuracy in surface-wave propagation particularly underneath oceans since probably in your model oceanic crust is now sampled by only one GLL point. That was the main motivation to start honouring Moho in global simulations where the oceanic crust is sampled by 1 spectral element (< 15 km) (thus there are 5 GLL points to sample it in the vertical direction) and the continental crust by 2 spectral elements (> 35 km). See Tromp et al. 2010 (Near real-time simulations of global CMT earthquakes, GJI) for the details.

So you may prefer or need to honour Moho in your perturbed model (then you will need to adjust the mesh according to your Moho perturbations) depending on what you would like to address in your experiments.

You can also send this to the CIG list to close the issue.

Good luck!
Ebru

-----------------

Ebru Bozdag
Assistant Professor

COLORADOSCHOOLOFMINES
Department of Geophysics
bozdag at mines.edu<http://www.minesnewsroom.com/email-signature-templates#> | tel: +1-303-273-3578  | fax: +1-303-273-3478


On 19 Jul 2017, at 08:46, Kendall, Elodie <elodie.kendall.14 at ucl.ac.uk<mailto:elodie.kendall.14 at ucl.ac.uk>> wrote:

Hi Ebru,

I set SUPPRESS_MOHO_STRETCHING = .true. in constant.h.in as you recommended and both the mesher and solver run perfectly now with no errors.

Thanks a lot!
Best wishes,
Elodie

________________________________
From: Ebru Bozdag <bozdag at mines.edu<mailto:bozdag at mines.edu>>
Sent: 07 July 2017 01:33
To: Kendall, Elodie
Subject: Fwd: [CIG-SEISMO] Specfem with an altered crustal model

I also forward my response to you directly as there are quite some confusions recently with my email addresses.

Ebru

-----------------

Ebru Bozdag
Assistant Professor

COLORADOSCHOOLOFMINES
Department of Geophysics
bozdag at mines.edu<http://www.minesnewsroom.com/email-signature-templates#> | tel: +1-303-273-3578  | fax: +1-303-273-3478



Begin forwarded message:

From: Ebru Bozdag <bozdag at mines.edu<mailto:bozdag at mines.edu>>
Subject: Re: [CIG-SEISMO] Specfem with an altered crustal model
Date: 6 Jul 2017 18:31:26 MDT
To: <cig-seismo at geodynamics.org<mailto:cig-seismo at geodynamics.org>>

Hi Elodie,

Are you honouring the crustal thickness in your simulations, i.e., are you using

! to suppress element stretching for 3D moho surface
  logical,parameter :: SUPPRESS_MOHO_STRETCHING = .false.

in your constant.h file? If this is the case perhaps after you add perturbations you may also be distorting the mesh aspect ratio at some locations.

Just try to run the mesher and the solver by setting SUPPRESS_MOHO_STRETCHING = .true. and see if you still have the same problem, if you have not tried it yet.

Best regards,
Ebru


-----------------

Ebru Bozdag
Assistant Professor

COLORADOSCHOOLOFMINES
Department of Geophysics
bozdag at mines.edu<http://www.minesnewsroom.com/email-signature-templates#> | tel: +1-303-273-3578  | fax: +1-303-273-3478







On 06 Jul 2017, at 02:32, Kendall, Elodie <elodie.kendall.14 at ucl.ac.uk<mailto:elodie.kendall.14 at ucl.ac.uk>> wrote:

Hi there,

I was hoping to ask you a question about Specfem3d_globe please? I have been using it a few months now and I am currently trying to introduce crustal thickness perturbations into crust2.0 and analyse the effect on the synthetics. I have set up a new crust2.0 which has 16,200 keys (one for each 2 by 2 degree grid) but the same layers for each grid. I have altered the corresponding subroutines for this new set of keys, no errors with the mesher and solver- same synthetics as before. Now, I add the perturbations to each layer of each grid in my crust2.0 model. I have changed the maximum moho depth from 90 to 115 (the new max.), the mesher runs fine but the solver fails with error "forward simulation became unstable in fluid and blew up". I have triedchanging the time step DT to DT*0.95 and DT*0.8 in the script shared/
get_timestep_and_layers.f90 however the same error appears. I was hoping you could help me please?

Thanks a lot,
Elodie Kendall

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