[CIG-SEISMO] Noise simulation in SPECFEM2D

[Yingzi Ying]

Dear Yang and Jeroen,

Thank you so much for help and very helpful recommendations.

I just re-ran the original noise_uniform example and plotted the 
seismogram received by 1st station in CAB_POS/step_2, and it is 
attached. Here the 1st station is slave and the 3rd station is master, 
and their distance is 100km(same case as in Tromp10). We see that the 
waveform of the 2nd half is still NOT in accordance with positive branch 
of cross-correlation in the paper.

As indicated in the manual of SPECFEM3D, the length of cross-correlation 
is the double size of NT, i.e., 2*NT-1. So if I only cut the second 
half, the total length of cross-correlation will be as long as NT(3000 
points here). I am confused.

Do you have any further suggestion? It will be appreciated if you would 
send me a copy of noise_tomography.f90 in your version. My copy of 
SPECFEM2d and examples are from the tar file in the mainpage.

Thanks again for help.

Best,
Yingzi
On 01/28/2013 08:54 PM, Yang Luo wrote:
> Hi Jeroen & Yingzi,
> I didn't implement the 2D version, which was actually done by Ryan
> (cc-ed) based on the 3D code we have already had.
> But I just checked the 2D code again and ran the example Yingzi
> mentioned, all looks good to me.
> The code I have may not be current, since I cannot use svn to get the
> latest version.
> But since the older version I have works, I assume the latest one should
> work as well.
> Yingzi, please see my following two cents, and make sure that you didn't
> misunderstand what you have already obtained from your tests.
> 1. the positive branch --- it refers to the second half (i.e., 60 to 120
> s for the example) of the seismograms you obtained (not for t>0 in the
> simulation).
> In other words, our simulation actually should start from t=-60s, but to
> avoid introducing this complexity, the time axis has been shifted.
> Given this into consideration, I think what you saw (i.e., two envelops)
> in your seismograms is correct.
> You just missed the point that the time from the simulation (almost
> always positive) is not the cross-correlation time (could be negative).
> Tromp et. al. (2010) provides step-by-step figures, which I think you
> might not fully understand yet.
> 2. the time_function_type --- you are right, the default should be
> changed to the one that reads in the file S_squares.
> But for benchmarking purposes, it is fine to put the one we have used in
> our paper.
> (Ryan, could you please fix that? just provide a default S_squres file
> there using the time_function you hard coded).
> 3. nu_master --- it refers to the noise direction, which is trivial in 2D.
> Yingzi, should you still be confused or claim that what you saw is
> totally different from the paper,
> please provide a picture of what you saw.
> Thanks,
> Yang
>
>
> On Mon, Jan 28, 2013 at 11:45 AM, Jeroen Tromp <jtromp at princeton.edu
> <mailto:jtromp at princeton.edu>> wrote:
>
>     Hi Yang:
>
>     A question for you.
>
>     Best regards,
>
>     Jeroen
>
>
>     Begin forwarded message:
>
>>     *From:* Yingzi Ying <yingzi.ying at me.com <mailto:yingzi.ying at me.com>>
>>     *Date:* January 28, 2013, 11:18:00 PST
>>     *To:* "cig-seismo at geodynamics.org
>>     <mailto:cig-seismo at geodynamics.org>" <cig-seismo at geodynamics.org
>>     <mailto:cig-seismo at geodynamics.org>>
>>     *Subject:* *[CIG-SEISMO] Noise simulation in SPECFEM2D*
>>     *Reply-To:* <cig-seismo at geodynamics.org
>>     <mailto:cig-seismo at geodynamics.org>>
>>
>>     Dear Tromp, Dimitri and all,
>>
>>     I am interested in noise simulation with SPECFEM2D(V7.0.0) to get
>>     ensemble cross-correlation. I tried to reproduce the result in
>>     fig. 2(a)
>>     in Tromp's paper "Noise cross-correlation sensitivity kernels" by
>>     executing ./process.sh in EXAMPLES/noise_uniform/.
>>
>>     My calculated interferogram after step 2 has two envelopes in the
>>     positive branch, and their positions are unconcerned with the time
>>     delay
>>     between two stations. This is totally different with the Tromp's
>>     result.
>>
>>     I checked the source code "noise_tomography.f90" and found the value
>>     "time_function_type" is fixed to "4", which means the variable
>>     "time_function_type" in "DATA/SOURCE" will not take action and the
>>     "DATA/NOISE_TOMOGRAPHY/S_squared" will not be read. Furthermore,
>>     there
>>     is no "nu_master" in SPECFEM2D, which exists in 3D version.
>>
>>     I don't know what goes wrong, and what I should do to get a correct
>>     ensemble interferogram. Anyone who knows please kindly give me a hint.
>>
>>     Thanks in advance.
>>
>>     Best,
>>     Yingzi
>>     _______________________________________________
>>     CIG-SEISMO mailing list
>>     CIG-SEISMO at geodynamics.org <mailto:CIG-SEISMO at geodynamics.org>
>>     http://geodynamics.org/cgi-bin/mailman/listinfo/cig-seismo
>
>

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