F-K

[giuliana]

Good morning,
I have some problem with F-K usage.
I have seven .sac files form a seismic array and I try to process them with F-K function.


The log messages are these:

******Selected from File 206.0940-1000.05-10.921A.1.sac+File 206.0940-1000.05-10.921B.1.sac+File 206.0940-1000.05-10.921C.1.sac+File 206.0940-1000.05-10.921D.1.sac+File 206.0940-1000.05-10.921E.1.sac+File 206.0940-1000.05-10.985A.1.sac+File 206.0940-1000.05-10.9EAA.1.sac ***********
Add signal id 1 to component Vertical of station 921A at 33.26 83.53 -12345
Add signal id 2 to component Vertical of station 921B at 110.61 110.95 0
Add signal id 3 to component Vertical of station 921C at 51.03 172.46 0
Add signal id 4 to component Vertical of station 921D at 62.87 122.95 0
Add signal id 5 to component Vertical of station 921E at 70.36 97.72 0
Add signal id 6 to component Vertical of station 985A at 38.65 128.37 0
Add signal id 7 to component Vertical of station 9EAA at 79.55 143.87 0
Found 7 different stations

Station '921C': incompatible sampling from 34800.9 to 36000.9 s, skipping range
Station '921C': incompatible sampling from 34800.9 to 36000.9 s, skipping range
Station '921C': incompatible sampling from 34800.9 to 36000.9 s, skipping range
Station '921C': incompatible sampling from 34800.9 to 36000.9 s, skipping range


I read that the problem could be that there isn't the same sampling frequency between different stations, but in this case all seven stations have the same sampling frequency (100 Hz).

What could be the problem with this data?
I have attaced the .sac files, divided in two folders.

Thanks in advance.

Giuliana

[admin]

Code: Select all

Name  Component TimeReference        T0              EndTime         SampFreq
921A  Vertical  25/07/2007 00:00:00  9h40m0.935000s  10h0m0.945000s  100
921B  Vertical  25/07/2007 00:00:00  9h40m0.855000s  10h0m0.865000s  100
921C  Vertical  25/07/2007 00:00:00  9h40m0.889000s  10h0m0.899000s  100
921D  Vertical  25/07/2007 00:00:00  9h30m0.994000s  10h0m1.004000s  100

This is just an example from your array1. At 100 Hz, the sampling period is 0.01s. The differences between the various T0 is not a multiple of the sampling period, hence the samples are not correcting synchronized across the whole array. You have two options:

• Forget about sub-sampling period time errors and round all your T0 to a 0.01 precision. It can be achieved with a single line script in menu 'Edit/Set header'
• Do a precise job and re-sample all signals to have a consistent sampling aligned to plain seconds. You can do it with menu 'Waveform/Phase shift'.