9. Distance trace plot with GMT, TRACE_PLOT (Unix only)

TRACE_PLOT is a simple program to create a distance trace plot using GMT version before 5 programs (Generic Mapping Tools, http://gmt.soest.hawaii.edu/). The axes of the plot are time and distance, and the traces are centered on the respective epicentral distance. The input to the program is a single event in Nordic format (S-file). From the S-file, the program reads the origin time, epicenter location and the names of the associated waveform files. TRACE_PLOT reads the waveform data and writes the x-y coordinates of the lines in the plot to a file that is then used as input to the GMT program psxy. The TRACE_PLOT program removes the DC from the data and as an option can apply a band-pass filter. The output of the program is a Postscript file (trace_plot.ps) and a batch file that can be modified and used to rerun the GMT programs (trace_plot.bat). The parameters are set in the trace_plot.par file, which can be located either in the DAT or in the working directory. An example is seen in Figure 9.1 .

The parameters in trace_plot.par are:

FILTER: The pass-band filter limits can be specified through the FILTER parameter.
DISTANCE: The distance range (y-axis) for the plot.
TIME: The time range in seconds (x-axis).
AMPLITUDE_SCALE: The amplitudes are scaled for every trace individually, by [amplitude/(max amplitude) * AMPLITUDE_SCALE].
STATION_SFILE_ONLY: This variable can be set to 1.0 to only plot traces that are listed in the S-file, the default is 0., which plots all traces without checking if they are present in the S-file.
TIME_ORIGIN: In the current version, the origin of the time axis corresponds to the origin time of the event.
COMPONENT: This can be used to select components for plotting, in case no component is defined, TRACE_PLOT will show all vertical component traces.

Example of trace_plot.par:

KEYWORD............Comments.............Par 1.....Par 2

FILTER             filter range         0.1       5.0
DISTANCE           dist range           0.        440.
TIME               time window          0.        250.
AMPLITUDE_SCALE    amplitude/max*scale  15.
STATION_SFILE_ONLY 0. if any station    0.
                   1. if station has
                      to be in s-file
TIME_ORIGIN        1.=origin time       1.
                   0.=file start time   
COMPONENT                               BH Z
COMPONENT                               HH Z

Figure 9.1: Example of TRACE_PLOT output.