Hi all，
Recently， I want to test a model about Eastern Tibet include a weak lithosphere (left) and a strong lithosphere (right). As mentioned in much of the literature, this lateral difference in viscosity may be one of the causes of steep topography.
To ensure equilibrium, I gave an initial topography of 1.8km for the left plateau.
But I checked the final output of the terrain data and found the following problem：
1、In the middle of the model, it also shows significant negative topography, and the difference in topography reaches more than 8km, which is a large difference from the actual. (as follow figure)
2、It seems to me that the weak lithosphere on the left side should be uplifted as a whole, and the lithosphere on the right side is difficult to deform significantly because it is stronger.
Thank you for posting the question to the forum. If plot velocity vectors on the images above, I suspect what you may see is flow in the asthenosphere that drives the evolution of topography to its current state.
Designing models with initial topography or lateral variations in lithospheric structure with a free surface is quite challenging. This is in part due to the fact that even if ensures isostatic equilibrium at a given depth by adjusting by surface topography and subsurface structure, there will be missing variations in elastic stress that would also act to support topography.
To assist further, it would be helpful to know exactly what hypothesis and processes you are trying to model. Is the goal to understand what lithospheric structure and rheology will reproduce current topographic patterns, or are you interested in the evolution of how topography will evolve from a given set of initial conditions? The model design and assumptions will likely be quite different between these two scenarios.
Aside, I suggest adding velocity vectors to your images and see what is driving the evolution of topography in your current results.
Thanks for your answer.
Yes，my goal is to understand what lithospheric structure and rheology will reproduce current topographic patterns. Because the present-day topography is an effective constraint on the dynamical reconstruction of mountain-building regions.
In my model, the lithospheric extrusion velocity is 2cm/y, and to ensure conservation of matter, the outflow velocity of the asthenosphere is 0.66cm/y, cf. Kinematically-driven 2d oceanic subduction in cookbooks.
The initial and final velocity fields are shown below, respectively:
Hi @HangWu - the initial velocity pattern you get seems correct, and the final flow field is almost certainly from ensuing adjustments to the lithospheric structure. One thing you could try is to remove the inflow/outflow boundary conditions to ensure that the model evolution is indeed behaving in a physically consistent manner. Beyond that, I think further adjustments to the model design fall more under the category of the research project itself.
