# F-K array

Hello everyone,

I am using Obspy to F-K anaisis. Some questioins I would like to ask.

1. Some theory about what method Obspy do,
a) the rel. power is refered to the semblance for an specific frequency in which the scipt find the maximum??
b) The F-K method of obspy return the maximum value of power for an specific frequency or the maximum of the mean beampower between freqlow and freqhigh( I mean broadband F-K)

2. Related with arguments of array_processing
a) How can I plot slowness map (Sx Sy, beampower) from one specific time window (any suitable script for this porpuse??)
b) How can I know in wich frequency , obspy have found the maximum beampower at a specific time window??
c) I think that by default is store=None, is it true?? if I place store=not None I will be able to plot slowness map, I don’t fully understand this command.

Thank you anyone can give some light to this questions or share some piece of scripts to find the solution.

Hi Roberto,

� a) the rel. power is refered to the� semblance for an specific frequency in which the scipt find the maximum??
Not quite sure what you mean here but if you are looking for the script that preforms the f-k analysis its called bbfk.c and should be located in …/obspy/obspy/signal/src

� b) The F-K method of obspy return the maximum value of power for an specific frequency or the maximum of the� mean beampower� between freqlow and freqhigh( I mean broadband F-K)�
� It is broadband f-k, so sum over all frequencies between freqlow and freqhigh.

a) How can I plot slowness map (Sx Sy, beampower)� from one specific time window (any suitable script for this porpuse??)
Obspy by default does not output this information but you can force it to by settting the kwarg “store” in the array_processing function. Something like,

from obspy.signal import array_processing, dump

kwargs = dict(
��� # slowness grid: X min, X max, Y min, Y max, Slow Step
��� sll_x=-3.0, slm_x=3.0, sll_y=-3.0, slm_y=3.0, sl_s=0.03,
��� # sliding window properties
��� win_len=1.0, win_frac=0.05,
��� # frequency properties
��� frqlow=1.0, frqhigh=8.0, prewhiten=0,
��� # restrict output
��� semb_thres=-1e9, vel_thres=-1e9, timestamp=‘mlabday’,
��� stime=stime, etime=etime, store=dump
)
out = array_processing(st, **kwargs)

This will save the data in the current working directory. You can then load and plot it.

�b) How can I know in which frequency , obspy have found the maximum beampower at a specific time window??
Obspy does not output this information, to get it you would need to modify the script bbfk.c or run in many narrow frequency bands.

�c) I think that by default is store=None, is it true?? if I place store=not None I will be able to plot slowness map, I don’t fully understand this command.
I think part a) answers this.

best,
Dave