[MSNoise] MSNoise Digest, Vol 31, Issue 1

Thu Oct 6 19:26:06 UTC 2016

Hi,
I will use this correspondence for my question, since you already mentioned removal of the response.

Do i have to change the code or something if I have different stationxmls for different years, so they are read correctly, or does the code manage this and i just put them into the folder?

Thanks

________________________________
From: msnoise-bounces at mailman-as.oma.be <msnoise-bounces at mailman-as.oma.be> on behalf of Flinders, Ashton <aflinders at usgs.gov>
Sent: Thursday, October 6, 2016 7:38:40 PM
To: Python Package for Monitoring Seismic Velocity Changes using AmbientSeismic Noise
Subject: Re: [MSNoise] MSNoise Digest, Vol 31, Issue 1

Thanks Esteban,

I have looked through the documentation extensively, as well as the SRL
paper, and a bit of grepping on the source code (e.g. it took me a while to
figure out why in the world I couldnt remove instrument responses using a
RESP or PZ file, since it is listed on the documentation page, until I
grepped the source code and saw those were not implemented.)

1) Yes. It is more efficient to compute the cross-correlation functions or
Green’s functions using 30-min chunks. Although you can change this feature
if you will. Segments are re-build afterwards.

This is only true if the daily segments are always preloaded into memory
(IO vs CC time). The SRL paper makes it sounds like this is the case, but I
want to make sure that this is always the case, even for processing many
stations/days or long segments. I also wasnt sure if these segmented CC
were used for any statistics (e.g. uncertainty in daily CC values).

2) You need to define the filters in order to compute the
cross-correlations and extract the coherent part of the ambient noise for a
given frequency range. MWCS is used to compute the moving window cross
spectral analysis after the cross-correlation procedure.

Yes, I understand that (the way its been written) filter values should be
defined before the CC (which really should only be the whiteneing band or
preprocessing), however I dont understand why in the web gui the whiten and
MWCS filters are put within the same group. This make me predefine a MWCS
filter band, along with my whiten band, even though the MWCS doesnt happed
for another two processing steps. This leads to confusion, for example;

What happens if I compute the CC's with a defined filter (as written, a
MWCS and whiten filter defined together) and then want to compute different
MWCS's later on when I actually get to the MWCS step. Can I just define a
new filter, with new mwcs_low mwcs_high values? Since the web gui forces me
to define a filter high low value (whiten, I assume) does it not use these?
Do I have to go back and recalculate the cross correlations everytime I
want to add an MWCS filter (which I wouldnt expect I have too)?

Similarly, what happens if I want to delete a set of processed MWCS or
stacks? I cant just delete the folder, since their are still pointers in
the sql database. Just reprocessing doesnt seem to work either.

thanks again

-ashton

On Thu, Oct 6, 2016 at 10:17 AM, Esteban Chaves <echfisica at gmail.com> wrote:

> Hi Ashton,
>
> As an active user:
>
> I highly recommend you to check the documentation: http://msnoise.org/doc/
> workflow.html#module-msnoise.s03compute_cc <http://msnoise.org/doc/
> workflow.html#module-msnoise.s03compute_cc>
> I think the pre-processing and processing steps are well documented in the
> web site.
>
> 1) Yes. It is more efficient to compute the cross-correlation functions or
> Green’s functions using 30-min chunks. Although you can change this feature
> if you will. Segments are re-build afterwards.
>
> 2) You need to define the filters in order to compute the
> cross-correlations and extract the coherent part of the ambient noise for a
> given frequency range. MWCS is used to compute the moving window cross
> spectral analysis after the cross-correlation procedure.
>
> 3) dunno. May be Thomas can give you more info.
>
> -Esteban J. Chaves
>
>
> > On Oct 6, 2016, at 5:00 AM, msnoise-request at mailman-as.oma.be wrote:
> >
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> > Today's Topics:
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> >   1. new user (Flinders, Ashton)
> >
> >
> > ----------------------------------------------------------------------
> >
> > Message: 1
> > Date: Wed, 5 Oct 2016 13:10:53 -0700
> > From: "Flinders, Ashton" <aflinders at usgs.gov>
> > To: <msnoise at mailman-as.oma.be>
> > Subject: [MSNoise] new user
> > Message-ID:
> >       <CAPbWHEO7J_9dyMdKJ3SQkpGy9hG7N1M-COwgzGTpkVmy85ig5g at mail.gmail.
> com>
> > Content-Type: text/plain; charset="UTF-8"
> >
> > Hi all, long-time obspy user new MSnoise user.
> >
> > I just had a couple quick questions I was hoping to get clarification on;
> >
> >> From the SRL article;
> > "Once all waveforms are loaded in memory, the computation is done by
> > iteration of the station pairs, on the different components to compute
> and
> > the on the different filters for each defined window (30 minutes slices
> by
> > default)."
> >
> > 1) To be clear, the two time-series from a station-station pair are
> divided
> > into segments (30 minutes long, no overlap, by default), and the CC is
> done
> > on these segments? Are these segments then rebuilt into the daily CCF? Is
> > this segmentation purely for efficieny reasons, or is there something
> else
> > going on?
> >
> > 2) Why does msnoise compute_cc, not work if there is no MCWS filter
> defined?
> >
> > 3) Is there an intelligent way to search the mailing list archive?
> >
> > Thanks for the help!
> >
> > -ashton
> >
> >
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> > End of MSNoise Digest, Vol 31, Issue 1
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--
Ashton F. Flinders, Ph.D
U.S. Geological Survey
345 Middlefield Road
Menlo Park, CA 94025
(650) 329-5050
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