24. Quick plotting and changing of phases and polarities, PLOTPHASE and PLOTPOLARITY

PLOTPHASE and PLOTPOLARITY are two programs for relatively quick and dirty plotting of short data segments. The purpose of these tools is to efficiently display observations that are stored in the sfile. They also allow to make simple adjustments. Both tools can be started from the command line or EEV (commands QP and POL).

PLOTPHASE takes the s-file name as input and plots a time window of data around all phase picks found in the s-file. The user specifies the window length. The tool allows to change picks, apply filters (given by characters that are the same as defaults in MULPLT), go forward or back to start if many channels. All commands are displayed on the screen (Figure 24.1). To start from the command line, use e.g.:

plotphase 09-2257-08L.S201508

Figure 24.1: Sample plot of PLOTPHASE.

PLOTPOLARITY takes the s-file name as input and makes a plot of P-wave onset with polarity readings if available. The program provides an efficient way to plot and change polarities used to determine fault plane solution. Only vertical channels of data are shown. If changes are done, the program will save, if the user wants to, these back to the s-file. The plots can extend over several pages when there are many traces.
PLOTPOLARITY can be started from EEV using command 'pol', or from the command line using either, e.g.:

plotpolarity 09-2257-08L.S201508

to plot traces which have polarities in s-file already, or with:

plotpolarity 09-2257-08L.S201508 all

to plot all vertical channel data. This is the default option when starting the program from EEV.
The program asks for some input at the startup:

  total window duration (default 1s): 
2

This is the total window duration that will be displayed around the P arrival, which is taken from the s-file.

  P-onset position as percentage of total duration (10-90; def 50 = middle):
60

This number gives the position of the P arrival within the time window as percentage of the total window. Setting this to 0 would mean that the signal starts from the P arrival, 50 means that P will be in the center of the window, and so on. Numbers less than 10 and greater than 90 will be reset to 10 and 90, respectively. One typically wants enough pre-phase time to see how the signal is changing.

  window length in seconds for averaging (default is 0)

This allows to average the samples for the given time period starting the given length prior to the time of a sample. The averaging will act as a filter without a phase response, and can be looked at for noisy signals, best only to confirm if the signal seen on original trace is still the same when applying averaging filter.
Next the plot comes up, and the polarities can be inspected and changed, using keys c=compression, d=dilatation and r=remove. In case of a change, a message is written to the terminal, and the graphics are updated. For each trace, the station name is shown together with the the phase, the polarity (empty if not available), the distance and azimuth. The graphics are written to a Postscript file polarity.eps, an example is given in Figure 24.2.

Figure 24.2: Sample plot of PLOTPOLARITY.