[CIG-SHORT] Questions about calculation of afterslip

[Charles Williams]

Dear Tu,

In answer to your question about why the fault tractions change following the coseismic displacement, I suspect it’s due to stress relaxation in the viscoelastic material.  Please note that this is a quasi-static problem.

As far as the tractions for afterslip, that’s somewhat dependent on what you want to represent.  One approach would be to run a set of simulations to get your tractions:

1.  Gravitational component could be obtained by running a simulation with no fault slip but with gravity turned on.  The tractions on the fault would give you the gravitational stress components you need.
2.  The components due to coseismic fault slip could be obtained by just running the elastic solution for the coseismic slip.

You could actually combine problems 1 and 2 as a single problem, and use those as initial tractions for your afterslip problem.  You would need to change your fault type do dynamic rather than kinematic.  If you also need to include tectonic loading, you would probably approximate that as a shear stressing rate in the direction of plate convergence.

Cheers,
Charles

p.s.  The mesh used in the example problem would not be suitable for a dynamic problem.



> On 27/11/2017, at 1:37 AM, tu xiang <tuxiang2016 at outlook.com> wrote:
> 
> hello,
> I notice that the slips at the slab in example 3d/subduction/step02 jump at the time of 10.0 year and do not change during the next 190 years while the traction_change at the slab in the example also jump at the time of 10.0 year but they also changed in the next 190 years. Then , Why?
> 
> I want to simulate the coseismic dynamic rupture and then simulate the afterslip generated by the rupture in 3D model.
> 
> But I do not know how to calculate the afterslip tractions on the fault in 3D model.  
> Is it like this:
> normal_stress=density*gacc*depth
> strike_shear_stress=?
> dip_shear_stress=?
> 
> normal_stress= normal_stress+normal_stress_change
> strike_shear_stress=strike_shear_stress+strike_shear_stress_change
> dip_shear_stress= dip_shear_stress+dip_shear_stress_change
> 
> Hope someone would like to tell me how to deal with these questions.
> 
> Best regards,
> Tu Xiang
> 
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Charles Williams I Geodynamic Modeler
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