## PSN-L Email List Message

Subject: Re: Integration and Winquake
From: John Hernlund hernlund@............
Date: Mon, 01 Jul 2002 16:18:23 -0700

```In practice, the FFT can be used to very easily obtain the integral or
derivative of a time series (i.e. division or multiplication of all
spectral points by i*frequency respectively). Since this is already
built into Winquake, this would be the most efficient method, and is the
one I always assumed was being used by Winquake. In this case there is
no finite integration step, since the FFT is a sinusoidal fit, which is
then played with.

Randall Pratt wrote:

>Arie,
>
>summing as you thought and also the possibility of maybe trapazoidal areas
>with several points.  Another question I have is how the result can begin at
>other than zero displacement with a velocity sensor and zero time at file
>start?  I wonder if the algorithym starts in the middle or from some average
>point and works to the ends?
>
>Randy
>
>----- Original Message -----
>From: "Arie Verveer"
>To:
>Sent: Tuesday, June 25, 2002 6:28 AM
>Subject: Integration and Winquake
>
>
>
>
>>Hi, Just a small question;  When integrating data with Winquake
>>does anyone now the integration period.? I would assume the integrated
>>value is the sum of the y values times 1/ ( sample rate ) over the length
>>of the integration period? . I'm probably wrong, any idea's.
>>
>>
>>Cheers
>>
>>Arie
>>__________________________________________________________
>>
>>Public Seismic Network Mailing List (PSN-L)
>>
>>To leave this list email PSN-L-REQUEST@.............. with
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>>
>
>__________________________________________________________
>
>Public Seismic Network Mailing List (PSN-L)
>
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>

In practice, the FFT can be used to very easily obtain the integral or derivative
of a time series (i.e. division or multiplication of all spectral points
by i*frequency respectively). Since this is already built into Winquake,
this would be the most efficient method, and is the one I always assumed
was being used by Winquake. In this case there is no finite integration step,
since the FFT is a sinusoidal fit, which is then played with.

Randall Pratt wrote:

Arie,

summing as you thought and also the possibility of maybe trapazoidal areas
with several points.  Another question I have is how the result can begin at
other than zero displacement with a velocity sensor and zero time at file
start?  I wonder if the algorithym starts in the middle or from some average
point and works to the ends?

Randy

----- Original Message -----
From: "Arie Verveer" <ajbv@............>
To: <PSN-L@..............>
Sent: Tuesday, June 25, 2002 6:28 AM
Subject: Integration and Winquake

Hi, Just a small question;  When integrating data with Winquake
does anyone now the integration period.? I would assume the integrated
value is the sum of the y values times 1/ ( sample rate ) over the length
of the integration period? . I'm probably wrong, any idea's.

Cheers

Arie
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