localmag outputs vanishingly small magnitude values

[Branden Christensen]

Hi all:

Buenos dias. 

This one has me stumped. localmag is outputting hilariously low magnitudes (-15.8). Either I am on to some ground breaking science or something is buggering up the calculation. I wonder if the Gutenberg-Richter law holds at magnitudes this low? (see Boettcher et al.'s 2009 paper "Extension of Gutenberg-Richter distribution to MW -1.3, no lower

limit in sight" for some insights on this topic :)

I am sure the only thing that could be buggered is the poles and zeros files. 

I understand that Earthworm needs one modified-SAC-format response file per component where the poles&zeros are in radians and the constant in nanometers.

These were created as follows:

Download dataless seed volume from IRIS BUD sever.

rdseed -pf <dataless>

This outputs one SAC-formatted file per station per channel. E.g., SAC_PZs_CX_PB11_BHZ__2008.358.00.00.00.0000_2599.365.23.59.59.99999

cat SAC_PZs_CX_PB11_BHZ__2008.358.00.00.00.0000_2599.365.23.59.59.99999:

* **********************************

* NETWORK   (KNETWK): CX

* STATION    (KSTNM): PB11

* LOCATION   (KHOLE): 

* CHANNEL   (KCMPNM): BHZ

* CREATED           : 2012-07-17T19:30:36

* START             : 2008-12-23T00:00:00

* END               : 2599-12-31T23:59:59

* DESCRIPTION       : Plate Boundary Station PB11, Chile

* LATITUDE          : -19.760960

* LONGITUDE         : -69.655820 

* ELEVATION         : 1400.0 

* DEPTH             : 0.0  

* DIP               : 0.0  

* AZIMUTH           : 0.0  

* SAMPLE RATE       : 20.0

* INPUT UNIT        : M

* OUTPUT UNIT       : COUNTS

* INSTTYPE          : Streckeisen STS-2/N

* INSTGAIN          : 1.500000e+03 (M/S)

* COMMENT           : N/A

* SENSITIVITY       : 2.516580e+09 (M/S)

* A0                : 6.007700e+07

* **********************************

ZEROS 3

+0.000000e+00 +0.000000e+00

+0.000000e+00 +0.000000e+00

+0.000000e+00 +0.000000e+00

POLES 5

-3.700400e-02 +3.701600e-02

-3.700400e-02 -3.701600e-02

-2.513300e+02 +0.000000e+00

-1.310400e+02 -4.672900e+02

-1.310400e+02 +4.672900e+02

CONSTANT +1.511886e+17

I then created a file called PB11_BHZ_CX.pz and pasted:

ZEROS 3

+0.000000e+00 +0.000000e+00

+0.000000e+00 +0.000000e+00

+0.000000e+00 +0.000000e+00

POLES 5

-3.700400e-02 +3.701600e-02

-3.700400e-02 -3.701600e-02

-2.513300e+02 +0.000000e+00

-1.310400e+02 -4.672900e+02

-1.310400e+02 +4.672900e+02

CONSTANT +1.511886e+17

The last step was to convert the CONSTANT from meters to nanometers:

ZEROS 3

+0.000000e+00 +0.000000e+00

+0.000000e+00 +0.000000e+00

+0.000000e+00 +0.000000e+00

POLES 5

-3.700400e-02 +3.701600e-02

-3.700400e-02 -3.701600e-02

-2.513300e+02 +0.000000e+00

-1.310400e+02 -4.672900e+02

-1.310400e+02 +4.672900e+02

CONSTANT +1.511886e+26

Does anyone see a flaw in my methodology? Does anything stand out as wrong or suspicious?

Kind Regards, 

Branden C. Christensen

Director, OSOP

branden.christensen@osop.com.pa

www.osop.com.pa

Volcan, Panama

[mwit...@memphis.edu]

I always get this stuff confused, but I think the units of your original
constant are counts/meter. So to convert that you need to multiply by
10^-9 meters/1 nm. So the constant you're using is off by 18 orders of
magnitude.

Mitch

Center for Earthquake Research and Information (CERI)
University of Memphis Ph: 901-678-4940
Memphis, TN 38152 Fax: 901-678-4734

> CONSTANT +1.511886e+*26*

>
> Does anyone see a flaw in my methodology? Does anything stand out as wrong
> or suspicious?
>
>
>
> Kind Regards,
>
>

> *Branden C. Christensen*
> Director, OSOP
> *branden.c...@osop.com.pa*
> www.osop.com.pa
> Volcan, Panama
>
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[Jean-Marie SAUREL]

Hello,

Correct, I confirm, I made the same mistake two weeks ago.

And I was thinking about some sort of protection in localmag to discard
a station magnitude result if it is completely non-consistent with the
other station magnitudes.
And, of course, logging a warning about this station.
That should be a simple test to add in the code.

Regards.

Jean-Marie SAUREL.

Le 18/07/2012 18:04, mwit...@memphis.edu a �crit :

--
--------------------------------------
Institut de Physique du Globe de Paris
Observatoire Volcanologique et Sismologique de Martinique
Morne des Cadets
97250 Fonds St Denis
0596784141
Martinique - FWI

[Branden Christensen]

Gentlemen:

So even thought the INPUT UNIT is labelled as M for meters the units are in counts/meter? Oh...the details! I will modify the localmag wiki section on poles and zeros when I get this sorted.

Great ideas Jean-Marie. I had some fun with localmag in the late hours of last night. I was able to get it to output a magnitude of 50. That would probably rip the universe in half! The %g output from gmew was equally awesome.

B

On Jul 18, 2012 12:46 PM, "Jean-Marie SAUREL" <sau...@ipgp.fr> wrote:

Hello,

Correct, I confirm, I made the same mistake two weeks ago.

And I was thinking about some sort of protection in localmag to discard a station magnitude result if it is completely non-consistent with the other station magnitudes.
And, of course, logging a warning about this station.
That should be a simple test to add in the code.

Regards.

Jean-Marie SAUREL.

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Morne des Cadets
97250 Fonds St Denis
0596784141
Martinique - FWI

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[Jean-Marie SAUREL]

Hola Branden,

Magnitude 50 ?? I don't want to be there when this happens .....

It's always a bit confusing with the way of thinking of some response
file formats. In SAC pz case, INPUT UNIT is not the unit of the
constant, but, as you just figured out, the unit of the unity input
signal for you have so much "constant" counts...

And it's always puzzling, as many manufacturers express the sentivity,
in several units, where SEED format requires a gain .... Ah, the magic
of response files ...... ;)

Jean-Marie.

Le 18/07/2012 18:53, Branden Christensen a �crit :

> Gentlemen:
>
> So even thought the INPUT UNIT is labelled as M for meters the units are
> in counts/meter? Oh...the details! I will modify the localmag wiki
> section on poles and zeros when I get this sorted.
>
> Great ideas Jean-Marie. I had some fun with localmag in the late hours
> of last night. I was able to get it to output a magnitude of 50. That
> would probably rip the universe in half! The %g output from gmew was
> equally awesome.
>
> B
>
> On Jul 18, 2012 12:46 PM, "Jean-Marie SAUREL" <sau...@ipgp.fr

> <mailto:sau...@ipgp.fr>> wrote:
>
> Hello,
>
> Correct, I confirm, I made the same mistake two weeks ago.
>
> And I was thinking about some sort of protection in localmag to
> discard a station magnitude result if it is completely
> non-consistent with the other station magnitudes.
> And, of course, logging a warning about this station.
> That should be a simple test to add in the code.
>
> Regards.
>
> Jean-Marie SAUREL.
>
> Le 18/07/2012 18:04, mwit...@memphis.edu

> <mailto:mwit...@memphis.edu> a �crit :

>
>
> I always get this stuff confused, but I think the units of your
> original
> constant are counts/meter. So to convert that you need to
> multiply by
> 10^-9 meters/1 nm. So the constant you're using is off by 18
> orders of
> magnitude.
>
> Mitch
>
> Center for Earthquake Research and Information (CERI)

> University of Memphis Ph: 901-678-4940 <tel:901-678-4940>
> Memphis, TN 38152 Fax: 901-678-4734 <tel:901-678-4734>

> SAC_PZs_CX_PB11_BHZ__2008.358.__00.00.00.0000_2599.365.23.59.__59.99999
>
> cat
> SAC_PZs_CX_PB11_BHZ__2008.358.__00.00.00.0000_2599.365.23.59.__59.99999:
> * ******************************__****

> * NETWORK (KNETWK): CX
> * STATION (KSTNM): PB11
> * LOCATION (KHOLE):
> * CHANNEL (KCMPNM): BHZ
> * CREATED : 2012-07-17T19:30:36
> * START : 2008-12-23T00:00:00
> * END : 2599-12-31T23:59:59
> * DESCRIPTION : Plate Boundary Station PB11, Chile
> * LATITUDE : -19.760960
> * LONGITUDE : -69.655820
> * ELEVATION : 1400.0
> * DEPTH : 0.0
> * DIP : 0.0
> * AZIMUTH : 0.0
> * SAMPLE RATE : 20.0
> * INPUT UNIT : M
> * OUTPUT UNIT : COUNTS
> * INSTTYPE : Streckeisen STS-2/N
> * INSTGAIN : 1.500000e+03 (M/S)
> * COMMENT : N/A
> * SENSITIVITY : 2.516580e+09 (M/S)
> * A0 : 6.007700e+07

> * ******************************__****

> *branden.c...@osop.com.__pa
> <mailto:branden.c...@osop.com.pa>*
> www.osop.com.pa <http://www.osop.com.pa>

> Volcan, Panama
>
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[Paul Friberg]

Hi All,

Having localmag discard bad mags due to bad responses won't help people discover the response problem though. It should probably be an option to safeguard production systems, however....Jean-Marie, sounds like you are volunteering to make this change? ;^)

Note that localmag has a useMedian option to do median instead of averaging the station mags. This effectively throws out big outliers in magnitudes...

Cheers,

Paul

On Wed, Jul 18, 2012 at 1:46 PM, Jean-Marie SAUREL <sau...@ipgp.fr> wrote:

Hello,

Correct, I confirm, I made the same mistake two weeks ago.

And I was thinking about some sort of protection in localmag to discard a station magnitude result if it is completely non-consistent with the other station magnitudes.
And, of course, logging a warning about this station.
That should be a simple test to add in the code.

Regards.

Jean-Marie SAUREL.

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Observatoire Volcanologique et Sismologique de Martinique
Morne des Cadets
97250 Fonds St Denis
0596784141
Martinique - FWI

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Paul Friberg   p.fr...@isti.com
ISTI==Instrumental Software Technologies, Inc.
Phone 845.256.9290 FAX 845.256.9299

[mwit...@memphis.edu]

One way to think about might be as a transfer function for the system. You
have an input in units of meters and an output in units of counts. If you
convolve the input with the system transfer function, you get the output.
So in order to start with meters and transfer to counts, you have to convolve
with something thats counts/meters.

(of course we always start with the output so we have to deconvolve the
transfer function to get the input--and that's often an unstable operation).

>>>> E.g., SAC_PZs_CX_PB11_BHZ__2008.358.**00.00.00.0000_2599.365.23.59.**
>>>> 59.99999
>>>>
>>>> cat SAC_PZs_CX_PB11_BHZ__2008.358.**00.00.00.0000_2599.365.23.59.**
>>>> 59.99999:
>>>> * ************************************

>>>> * NETWORK (KNETWK): CX
>>>> * STATION (KSTNM): PB11
>>>> * LOCATION (KHOLE):
>>>> * CHANNEL (KCMPNM): BHZ
>>>> * CREATED : 2012-07-17T19:30:36
>>>> * START : 2008-12-23T00:00:00
>>>> * END : 2599-12-31T23:59:59
>>>> * DESCRIPTION : Plate Boundary Station PB11, Chile
>>>> * LATITUDE : -19.760960
>>>> * LONGITUDE : -69.655820
>>>> * ELEVATION : 1400.0
>>>> * DEPTH : 0.0
>>>> * DIP : 0.0
>>>> * AZIMUTH : 0.0
>>>> * SAMPLE RATE : 20.0
>>>> * INPUT UNIT : M
>>>> * OUTPUT UNIT : COUNTS
>>>> * INSTTYPE : Streckeisen STS-2/N
>>>> * INSTGAIN : 1.500000e+03 (M/S)
>>>> * COMMENT : N/A
>>>> * SENSITIVITY : 2.516580e+09 (M/S)
>>>> * A0 : 6.007700e+07

>>>> * ************************************

>>>> *branden.c...@osop.com.**pa <branden.c...@osop.com.pa>*

>>>> www.osop.com.pa
>>>> Volcan, Panama
>>>>
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>>>
>>
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>> ------------------------------**--------

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>> Observatoire Volcanologique et Sismologique de Martinique
>> Morne des Cadets
>> 97250 Fonds St Denis
>> 0596784141
>> Martinique - FWI
>>
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[Branden Christensen]

Paul:

Now I am getting reasonable magnitudes. Thanks for the insight on the median. I will implement it. Please not that the useMedian is not mentioned in the localmag.d file but it is mentioned in the wiki. So I just added the "useMedian" line to the end of the .d file. 

I corrected the localmag wiki "Response File Generation from Dataless" section. 

Thanks Mitch, Jean-Marie and Paul.

Here is a basic How-To I just put up on the creation of pz files: http://vps.isti.com/trac/ew/wiki/pz-files#Runrdseed

Best, 

Branden C. Christensen

Director, OSOP

branden.christensen@osop.com.pa

www.osop.com.pa

Volcan, Panama

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