23.6 Composite fault plane solution using any of the programs FOCMEC, FPFIT, HASH and PINV

For some small networks, the number of stations is too small to make a fault plane solution using polarities from a single event and even using amplitudes, there might not be enough data. Under the assumption that the underlying stress field will generate events with similar fault plane solutions, a group of events can be used together to make one fault plane solution which will represent an average of the supposedly similar solutions. The advantage of using several events with different azimuths and angles of incidence is that the observations will be well spread out on the focal sphere. The four fault plane solution programs in SEISAN can all be used to make a composite solution and both polarities and amplitudes can be used. The procedure is similar for all programs:

1:

Select the events to be used together in one file using e.g. SELECT or the graphical options in EPIMAP.

2:

Locate the events with HYP. There are now two output files, hyp.out and print.out available for input to the fault plane solution programs. The fps program must be executed in the directory of the print.out and hyp.out. Once the fault plane solution has been made, the solution is available with the first event in hyp.out.

3:

Do the fault plane solution:

-	FOCMEC: Run with command 'focmec'.
-	FPFIT. Run with command 'fptfit'.
-	HASH: Run with command 'hash_seisan'.
-	PINV: Run with command 'pinv'.

4:

Plot the composite fault plane solution: The solution can be plotted with command 'focmec o'. Only polarities will be plotted. The solution can also be plotted with plotfoc using hyp.out as input. In thsi case no polarities are shown. The solution with the first event in hyp.out is used. No agency is written for the composite solution. A previous solution without agency and quality is overwritten. If all 4 programs have been used, all 4 solutions will be present in hyp.out and plotted together. It is possible to plot stations corresponding with all polarities with program focmec. Then type 'focmec' and when the menu 0-4 comes up, chose -1.

The solution(s) will also be written to the cat-file fps.out in standard SEISAN format. For each run of a program, the solutions accumulate in fps.out. This can be used to compare solutions from different programs, see FOC. The solution can also be plotted with PLOTFOC. An example of the plot with FOCMEC is seen in Figure 23.1.

Finally the solutions will also be written to hyp.out and can be plotte with PLOTFOC, however in that case only the mechanisms are shown.

NOTE: All fault plane solutions made from the different programs are accumulated in file fps.out.

When the first event has been read in, general questions comes up. The all events are read in and after last event, there is info on the toal number of data, see example below:

c:\FPS>focmec


Number of polarities:           10
Amplitude types:   Manual:       4   Automatic:    0   Spectral:     0

Amplitude to use:  Manual(1), Automatic(2), Spectral(3) ?
1

 PCNG  use P-travel time to calculate S-travel time

 Q: Local: Qp= 470.0**0.70  Qs= 470.0** 0.7   Global: t*(P)=1.10  t*(S)=4.20

 STAT  C PH       AMP    PER TRTIME   QCOR ANGINC ANGEMG Fcor   AZ  DIST
 MESC  Z PG 103600000   0.14    1.4    1.0    128     20  1.9   54     3
 MESC  T SG 117800000   0.38    2.5    1.0    128     20  2.0   54     3
 VIF   Z PG   8745000   0.25    1.5    1.0    119     22  1.8  132     4
 VIF   T SG  22300000   0.21    2.7    1.0    119     22  2.0  132     4
 PMAT  Z PG  28400000   0.14    1.4    1.0    119     22  1.8    8     4
 PMAT  T SG  49800000   0.24    2.4    1.0    119     22  2.0    8     4
 PCNG  Z PG  17900000   0.14    2.0    1.0    107     25  1.8   96     7
 PCNG  T SG  29500000   0.34    3.5    1.0    107     25  2.0   96     7

 STAT  Ratio type  T     Amp 1    Amp 2  Fcor LogRat
 MESC  SH(T)/P(Z)  H 117800000103600000   0.9   0.03
 VIF   SH(T)/P(Z)  H  22300000  8745000   0.9   0.37
 PMAT  SH(T)/P(Z)  H  49800000 28400000   0.9   0.21
 PCNG  SH(T)/P(Z)  H  29500000 17900000   0.9   0.17
.
.
.
.
.
.
 Q: Local: Qp= 470.0**0.70  Qs= 470.0** 0.7   Global: t*(P)=1.10  t*(S)=4.20

 STAT  C PH       AMP    PER TRTIME   QCOR ANGINC ANGEMG Fcor   AZ  DIST
 MESC  Z PG  45300000   0.14    1.7    1.0    135     18  1.9   51     4
 MESC  T SG  36300000   0.17    2.9    1.0    135     18  2.0   51     4
 VIF   Z PG   1916000   0.21    1.7    1.0    132     19  1.9  125     4
 VIF   T SG  11700000   0.21    2.9    1.0    132     19  2.0  125     4
 PMAT  Z PG   3320000   0.10    1.6    1.0    128     20  1.9   11     5
 PMAT  T SG   8508000   0.07    2.8    1.0    128     20  2.0   11     5
 PCNG  Z PG   4310000   0.15    2.1    1.0    117     23  1.8   92     7
 PCNG  T SG   8371000   0.28    3.7    1.0    117     23  2.0   92     7


 STAT  Ratio type  T     Amp 1    Amp 2  Fcor LogRat
 MESC  SH(T)/P(Z)  H  36300000 45300000   0.9  -0.12
 VIF   SH(T)/P(Z)  H  11700000  1916000   0.9   0.76
 PMAT  SH(T)/P(Z)  H   8508000  3320000   0.9   0.38
 PCNG  SH(T)/P(Z)  H   8371000  4310000   0.9   0.25

 total obs = 126  gap in az =  56.0  gap in ain =  22.0

  Stop                     (0)
  Plot saved solution(s)   (1)
  Plot new solutions       (2)
  Plot selected solution   (3)
  Find new solutions       (4)
  -1, -2, -3 also plot station

Figure 23.2: Composite solutions using 5 events and the 3 programs FOCMEC, FPFIT and HASH. Only polarities are used.

Figure 23.2 shows an example using polarities from 5 events.