How can I assign two lithospheric thickness?

ASPECT
1

Hello.
Straightforwardly, I’d like to assign differently thickness underneath oceanic crust and continental crust.
However, ASPECT reads only a value for lithosphere thickness.
Do you guys have any idea?

I’like to impose prescribe velocity on two additional different lithospheric boundaries for the convergent situation.

2

Hi Sungho,

Thank you for posting!

Where exactly are you specifying a lithospheric thickness? I’m not sure if this is with respect to an initial thermal or compositional thickness, which would be specified in two different sections.

In any case, there are a number of options for prescribing more complicated initial conditions with two or more lithospheric plates:

  1. Use an external code to write ASCIII data files containing the initial temperature and composition structure, which are then read in by ASPECT.
  2. Write a new initial temperature and/or composition plugin within ASPECT.
  3. Use WorldBuilder, which is directly linked to ASPECT and allows one to quickly build complicated model setups.

Once we know a bit more about your specific requirements and preferences, it will be easier to point towards specific sections of the manual, tests, etc.

Cheers,
John

1 Like
3

Hello John :slight_smile:

Thank you for your reply.

Actually, this would be derived from my miss understood for boundary conditions.
I have a plan to simulate flat slab subduction and slab rollback modeling.
In order to do this, I have made a passive margin model (initial state) using GWB below two figures.

As I said before, I’d like to impose prescribe velocity on two additional different lithospheric boundaries (left and right) for the convergent situation (active margin).

In my knowledge, I cannot impose plate velocity on the top boundary because I have a plan to use free surface boundary condition on top (ASPECT provides no superpositions (i.e. I mean a mixed condition) of the boundary conditions?!).

For my purpose, I tried to use like these statements

subsection Geometry model
set Model name = box with lithosphere boundary indicators
subsection Box with lithosphere boundary indicators
set X extent = 2000e3
set Y extent = 660e3
set Lithospheric thickness = 50e3
set X repetitions = 4
end
end

The continental lithosphere has ~ 100 km thickness, however, I don’t have any idea to impose overriding plate velocity on the right continental lithosphere because only the lithosphere thickness indicator read a thickness.

Unfortunately, this is not related to initial temperature and initial composition but related to boundary conditions.

Best regards,
Sungho

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5

Hi Sungho,

Thanks for the clarification.

You are correct that there is not really an option to have the top boundary be both a free surface and have horizontal velocities imposed over part of the boundary.

This leaves the option of imposing horizontal plate velocities on the side walls, but the issue there is that the lithosphere has different thicknesses on the left and right walls. Is this an accurate summary of the issue?

If so, my suggestion would be to use a Lithospheric thickness of 100 km and have the horizontal velocities on the left lithospheric wall simply extend down to 100 km or linearly decrease from 50 - 100 km depth. What values are you planning to prescribe for the velocity BC beneath the ‘lithosphere’?

Cheers,
John

6

John;

Thank you for your reply
I understood what you meant
I would be really helpful. :slight_smile:

Thanks

Sungho