[CIG-SHORT] problem definition for Landers-Hector Mine benchmark

[Bradford H. Hager]

Brad and cig-short-

I am back from wondering in the wilderness and digging into  
benchmarking.  I have sped-read the literature on postseismic  
deformation following Landers, and have the following (revised)  
opinion about the viscoelastic structure.  Freed & Burgmann (Nature,  
2004) included a few newtonian models in their study focusing on  
power law, most of which included a Maxwell lower crust, as well as a  
Maxwell mantle.  Pollitz (EPSL, 2003) also investigated Maxwell  
models including a viscoelastic lower crust and mantle.   
Unfortunately, their layer boundaries do not coincide.  I suggest  
that we go with Pollitz' structure because it does not have an  
additional layer boundary in the mantle.

I suggest that we use the following viscosity structure:

0 - 18(?) km depth, elastic (e.g., visc = 10^25 Pa s)  Note - the  
precise depth is not crucial - use the depth closest to the layer  
boundary in the elastic structure.

18(?) - 30 km depth, Maxwell viscoelastic, visc = 32.2 x 10^18 Pa s.

30 - 150 km, Maxwell viscoelastic, visc = 4.6 x 10^18 Pa s.


I suggest that the solutions be examined at 0, 0.5, 1, 2, 4, and 7  
years so that we can follow the early transients better and end at  
about the time of Hector Mine.

I think that Brad's description of model output is good.

Brad Hager




On Jul 24, 2006, at 11:41 AM, Brad Aagaard wrote:

> Hi all:
>
> I would like to put the problem description together for the
> Landers-Hector Mine benchmark.
>
> I have the following tidbits in my notes from the Golden workshop:
>
> * Use mesh provided by Carl
> * Use Landers slip model provided by Yuri
> * Use layered material model provided by Brad
>   - viscosity is 10^18 Pa-s in lower-crust and mantle
> * Boundaries (lateral sides and bottom) are fixed displacements
> * Solution is computed at 0, 5, 10, 15 years
> * no gravity
>
> Issues that need to be resolved (please comment):
>
> 1. How is the slip model going to be defined? Are people getting the
> slip model info from attributes embedded in the LaGriT output or is
> Yuri providing a separate data file?
>
> 2. What depth range are we using for the lower-crust and mantle? I am
> guessing that we will use a viscosity of 10^25 Pa-s in the upper
> crust as we did for the reverse and strike-slip benchmarks, so at
> what depth do we jump to a viscosity of 10^18 Pa-s?
>
> 3. What comprises the "solution"? I am guessing that we want
> displacements and velocities at all of the nodes as we have done for
> the other benchmarks. In this case, we have additional faults (i.e.,
> Hector Mine faults), so we will want stress changes on those
> surfaces, right? I am guessing we want the traction vector computed
> at the quadrature points of the faces making up the Hector Mine
> faults.
>
> Brad
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