[CIG-SHORT] Pylith Green's functions

Thu Apr 7 19:10:04 PDT 2016

Hi Demian,

As you mentioned, my option #2 is just a quicker way of doing what you’re already doing, but you don’t have to read everything in, reform the stiffness matrix, etc.  I had an example once, but it was for a much older version of PyLith (before we had Green’s functions).  I’m afraid I don’t have anything around right now that would help you.  I haven’t thought about this for a while, but I think you could do this with the right sort of time history database, in conjunction with the proper time shift for each source (patch).  You would end up defining a separate source for each patch.

Cheers,
Charles

> On 8/04/2016, at 1:44 PM, Demian Gomez <demiang at gmail.com> wrote:
> 
> Hi Charles,
> 
> I thought so. What I'm doing is running a forward simulation for each patch. I estimated the times and even though Pylith has to load the matrices each time it starts a new patch (twice actually, once for strike slip and another for reverse) it takes much much less than running the Green's function problem. I didn't think of the time dependent problem that you suggested. This sounds like a very good solution. I'll try to implement this method. Do you have by chance an old slip time spatialdb where you did this, as an example?
> 
> Thanks,
> Demián
> 
> On Thu, Apr 7, 2016 at 6:17 PM, Charles Williams <willic3 at gmail.com <mailto:willic3 at gmail.com>> wrote:
> At present, I don’t think PyLith is set up to do this sort of thing.  Depending on your situation, I can think of two options:
> 
> 1.  Generate your Green’s functions in batches that can be done simultaneously.  You could define several subregions on your fault and run each of those separately.  This would work if you have a cluster or several workstations to run on.  Once all the functions are generated you can combine them however you like.
> 2.  Create a time-dependent problem where each patch uses a different slip history (you could write a script to generate this).  At t=0 you slip patch 0 by a positive amount, at t=1 you slip patch 0 by a negative amount (to cancel out the slip from the previous time step) and patch 1 by a positive amount, etc.  This was the sort of method we used before we had Green’s functions officially included in PyLith.
> 
> Cheers,
> Charles
> 
> 
>> On 8/04/2016, at 9:45 AM, Demian Gomez <ddgomez at memphis.edu <mailto:ddgomez at memphis.edu>> wrote:
>> 
>> Hello,
>> 
>> I have a model with a fault that is made of 16k nodes. I need the impulse responses to invert for the slip at the fault, but I've grouped the nodes into square slip patches (20 x 20 km). Therefore, I have ~ 200 patches that are formed by multiple nodes on my fault interface. Is there a way to run the Green's function problem in Pylith (2.1.0) with more than one impulse at the time? Running the problem with 16k nodes will take too much time and I don't need each individual node's impulse response, only the impulse response of each slip patch made of multiple nodes.
>> 
>> Thanks,
>> --
>> Demián D. Gómez
>> Graduate Research Assistant & PhD Candidate
>> Center for Earthquake Research and Information
>> 3890 Central Ave, Memphis TN 38152
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> Charles A. Williams
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Charles A. Williams
Scientist
GNS Science
1 Fairway Drive, Avalon
PO Box 30368
Lower Hutt  5040
New Zealand
ph (office): 0064-4570-4566
fax (office): 0064-4570-4600
C.Williams at gns.cri.nz <mailto:C.Williams at gns.cri.nz>
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