Geophysical Exploration of Crustal Structure

Exercise 1

Preparation

If you do not finish preparation, go back to preparation.

Looking and displaying data

SU data are composed of trace header part and data part for each trace. Here, a trace is one set of time-series data recorded at a receiver (geophone). The trace header contains basic information of each trace.

First, display the range of the values of each header keyword. Displaying all header values will result in a very long list of numerical values.

Display the header information of the file 'Nstack.su' used in Preparation.

$ surange < Nshots.su

"surange" is a command that "reads the header of each trace and outputs their range (minimum and maximum values)".

The output is as follows.

-----
2869 traces:                        : Number of traces
tracl    1 2869 (1 - 2869)          : Trace number
fldr     0 3383 (1092 - 3383)       : Shot number
tracf    0 96 (1 - 96)              : Receiver number
ep       69 2899 (994 - 2899)
cdp      1 2869 (1 - 2869)          : CDP number
cdpt     1
trid     1                          : Data type (1: seismic data)
nhs      0 72 (40 - 5)
offset   -870 0 (-170 - -170)       : Offset distance (m)
ns       2250                       : Number of samples in the trace
dt       4000                       : Sampling time (in micro second)
nofils   281 3149 (281 - 3149)
lcf      69 2899 (994 - 2899)
hcf      1
lcs      0 3383 (1092 - 3383)
hcs      0 96 (1 - 96)
year     0 207 (0 - 207)            : Time stamp
hour     0 23 (0 - 3)
minute   0 59 (0 - 39)
sec      0 59 (0 - 57)
grnors   0 72 (40 - 5)
-----

The "sukeyword" command will tell you the explanation of the header keywords.

$ sukeyword -o

Then, display the range of the header values of the file "Nshot.su" which you are going to use in this exercise.

$ surange < Nshots.su

The output is as follows (it will take time since the dataset is very large).

-----
19057 traces:                              : Number of traces
tracl    39069 58125 (39069 - 58125)       : Trace number
tracr    1 19057 (1 - 19057)               : Trace number
fldr     1687 2012 (1687 - 2012)           : Shot number
tracf    28 96 (96 - 28)                   : Receiver number
cdp      900 1300 (900 - 1300)             : CDP number
cdpt     1 69 (1 - 1)
trid     1 2 (1 - 1)                       : Data type (1: seismic, 2:dead)
offset   -2435 -170 (-170 - -2435)         : Offset distance (m)
scalel   -10000
scalco   -10000
counit   1
muts     0 11000 (0 - 0)
ns       5500                              : Number of samples in the trace
dt       2000                              : Sampling time (micro second)
day      206
hour     21 22 (21 - 22)
minute   0 59 (3 - 20)
sec      1 59 (45 - 3)
-----

You will find that this dataset contains 19057 traces, and each trace has 5500 samples.

Try displaying some of the header values of each trace in the data file. The output is an extremely long list of headers, so quit executing the command using 'Ctrl+C' without waiting for the headers of whole traces.

$ sugethw key=tracl,fldr,tracf,cdp,offset < Nshots.su

"sugethw" is a command that "displays the trace header values".
"key= " indicates the keyword to be displayed. Here, the keywords "tracl,fldr,tracf,cdp,offset" are to be displayed. They indicate the number of the trace, source, and receivers.

Note the order of the traces in the dataset.

Data selection and windowing

Try displaying a portion of the data "Nshots.su" since the dataset is large.

First, display the first 100 traces.
Next, display the next 100 traces.
Then, display the traces whose header key "fldr" value is ranging from 1800 to 1801.
Finally, limit the data time from 6.0 to 8.0 seconds.

$ suwind min=1 count=100 < Nshots.su | suximage perc=99 &
$ suwind min=101 count=100 < Nshots.su | suximage perc=99 &
$ suwind key=fldr min=1800 max=1801 < Nshots.su | suxwigb perc=99 &
$ suwind key=fldr min=1800 max=1801 tmin=6.0 tmax=8.0 < Nshots.su | suxwigb perc=99 &

"suwind" is a command that "apply a window to the data".
"key= " indicates the header key. "min= " and "max= " assign the range.
For time axis window, use options "tmin= " and "tmax= ".
"suximage" displays an image of the data in B/W or color. Pressing 'h', 'H' 'r', 'R' keys change the color pallet.
"suxwigb" displays wigle traces.
"perc= " indicates the display amplitude scale (in percentile). A smaller value amplifys the wave amplitude.
Click and drag of the left-mouse-button can zoom display.
Pressing 'q' kills the display.

Next, Extract a sample dataset from a larger dataset. Extract the traces whose CDP number lies between 1090 and 1110 and create a sample data file named "cdp_test.su".

$ suwind key=cdp min=1090 max=1110 < Nshots.su > cdp_test.su

Display the contents of the headers.

$ sugethw key=cdp,offset < cdp_test.su

Display an image of the data.

$ suximage perc=99 < cdp_test.su &

If you want to display waveforms,

$ suxwigb perc=99 < cdp_test.su &

This may give you a black window if you tried to display many traces at one time. Make sure that zooming in the waveform (by mouse drag) shows you the waveforms.

Fig: Shot gather.

Sort the order of the data in the order of the CDP number and then display them.

$ susort cdp < cdp_test.su | suximage perc=99 &

"susort" is a command that "sorts the data",
The data is sorted on the order of the given keyword.
Unlike to most SU programs, "susort" program can not handle pipes for input and output simultaneously. The following usage is recommended.
```
    $ susort < input > output
    $ susort < input | nextcommand
```

Homework

Using the sample data "cdp_test.su" you created,

Choose any one CDP number you like from 1090 to 1110,
Extract the traces whose CDP numbers are of your choice,
Sort the traces on the order of "tracf",
and apply a time window from 6.0 to 7.5 seconds.

Submit

a list of the command line(s) you used,
a wigle (waveform) display (not an image) of the data,
and the range of the header values of the traces (output of "surange").

Zooming figures using mouse operation is not what is intended here. Do use appropriate commands to do the job.

Delete the sample data after finishing your homework.

$ rm cdp_test.su

Preparation < Exercise 1 > Exercise 2

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Last modified: Wed Oct 18 18:50:37 JST 2023