[CIG-SEISMO] Source Time function

[Jeroen Tromp]

Hi Kasper:

It's possible, but I still would recommend low passing the seismograms 
to bring them within the numerical validity range. If you are doing a 
similation in a finite domain, e.g., a box with three absorbing 
boundaries and a free surface, then, yes, you also need to use a low 
frequency cut off to account for this. Thus a bandpass is the best option.

Best regards,

Jeroen



On 4/16/13 5:27 PM, Kasper VanWijk wrote:
> Kia Ora Jeroen!
>
> Greetings from Auckland. I noticed your advice to Martin about source 
> time functions. As you know, I am mostly an experimental guy, so 
> forgive me if I ask a trivial question, but I am working with a 
> student on extending Aki's SPAC method. It involves the summation of 
> many sources. When we use the Dirac option in SPECFEM2D (i.e. simulate 
> the Green function response), we get what you told Martin: good 
> signals in the range that the mesh supports. We have noticed, however, 
> that the high-frequency numerical noise seems to stack out. Is it well 
> known that this high-f noise is (apparently) uncorrelated? Or are our 
> eyes deceiving us?
>
> Also, are you aware of limitations on the LOW frequency information in 
> the data with the Dirac source,  or should those be  well represented?
>
> groet,
> kasper
>
>
>
>
> On Tue, Apr 16, 2013 at 4:18 AM, Jeroen Tromp <jtromp at princeton.edu 
> <mailto:jtromp at princeton.edu>> wrote:
>
>     Dear Martin:
>
>     Yes, you can. The way to do this is to calculate the imuplse response,
>     i.e., the Green's function, and subsequently convolve with
>     whatever you
>     choose to be your source-time function in postprocessing. Note
>     that you
>     will still have to bandpass the result to bring it within the
>     numerical
>     validity range, i.e., make sure you are resolving all the
>     frequencies of
>     interest with your mesh.
>
>     Best regards,
>
>     Jeroen
>
>
>     On 4/11/13 11:30 AM, Martin Martin wrote:
>     > Dear SPECFEM2D Team,
>     >
>     > I would like to know if it is possible to create my own source
>     function
>     > - I mean other than using the five time function which is provided :
>     > Rickett, gauss, heaviside, etc ?
>     >
>     > Thank you
>     >
>     > Best wishes,
>     >
>     > Martin
>     >
>
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