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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:

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

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.

Do the fault plane solution:

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

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.

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.

next up previous contents index
Next: 23.7 Moment tensor inversion Up: 23. Fault plane solution Previous: 23.5 Fault plane solution   Contents   Index
Peter Voss : Tue Jul 2 07:59:27 UTC 2019