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7.1.10 Preventing a local minimum

For some data, the iterations will stop in a local minimum. This can partly be checked with the DRMS output in the print.out file. The DRMS output gives the RMS in 6 points around the hypocenter at distance DRMS. DRMS is set with RESET TEST (13). In order to check for a local minimum, a more extensive grids search can be done. This is done by using RESET TEST 119-121. Setting these parameters, a grid search can be done in 3D around the hypocenter in a user selected grid size. The grid search is done after the last iteration. If a point is found with a lower RMS than given by the iterative process, a new iterative process is started with that point as start location. The grid search can be particularly useful for local earthquakes, however, in the current implementation it is also done for distant earthquakes using the same parameters. Note that using a large grid might significantly slow down the processing time.

When using the grid search option for start location, an extra ouput is given in the print.out file:

Grid rms smaller than solution rms 1.953 3.391

Hypocentral dist. (km) from epicenter to grid point min. 28.3

Depth change 10.00

Iterate again with new start location: 62.303 5.760 15.0

This information gives how far aways the minimum is and what the RMS is.


next up previous contents index
Next: 7.1.11 Alternative model Up: 7.1 The hypocenter program, Previous: 7.1.9 Starting location   Contents   Index
Peter Voss : Tue Apr 9 09:35:22 UTC 2019