[SAC-HELP] SAC APK parameters

[Matthew R. Agius]

Hi again,
I have went through Rex V. Allen, but i still haven succeed to get 
control of APK.
If I have in memory a 24hour sac file will it pick all events? Can 
someone share with the parameters used at their station?
Which sample rate is best for APK?

Regards,

Matthew




George Helffrich wrote:

> Dear Matthew -
>
> c3 and c4 are pure numbers, and serve as weights. Here is the part of 
> the algorithm that they act in:
>
> * - Compute first difference of filtered data.
> fdfd = fdnew-fdold
> * - Compute characteristic function.
> chf = fdnew**2 + c2*fdfd**2
> * - Compute the short term average.
> chfsta = chfsta + c3*(chf-chfsta)
> * - Compute the long term average.
> chflta = chflta + c4*(chf-chflta)
>
> You should look at the reference for more details on how to modify 
> these factors:
> Rex V. Allen, Automatic Earthquake Recognition and Timing from Single 
> Traces, BSSA, Vol. 68, No. 5, Oct. 1978.
>
> On Wednesday, February 1, 2006, at 07:45 AM, Matthew R. Agius wrote:
>
>     Hi Everyone,
>
>     I am trying to find my way with the SAC funciton APK.
>     I would like to alter the STA and LTA constants
>
>     The default values as qouted from online manual are:
>
>     DEFAULT VALUES:
>     APK C1 0.985 C2 3.0 C3 0.6 C4 0.03 C5 5.0 C6 0.0039 C7 100. C8
>     -0.1 D5 2. D8 3. D9 1. I3 3 I4 40 I6 3 VALIDATION ON
>
>     and that :
>
>     3. C3 is the timing constant, used to compute the short term average
>     of the characteristic function.
>
>
>     4. C4 is the timing costant used to compute the long term average
>     of the characteristic function.
>
>     My questions is what are the values of c3 and c4, are they minutes
>     or seconds?? 0.6 means 60 seconds? and 0.03 is 3 seconds?
>
>     Regards
>
>     Matthew
>     M.Sc Studnet
>     University of Malta
>
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>
> George Helffrich
> george at geology.bristol.ac.uk
>