7.1.9 Starting location

The program uses a starting location algorithm (reset test(56)) which tests the rms of all starting locations and select the minimum rms solution, see HYP manual. If test(56) is 0, then for local and regionl events, a grid of 20 points around the nearest stations is searched, distances 10, 50, 150, 450 and 800 km are used. If a distant event, a grid of 98 points following the major seismic zones is used. If test(56) is 1, the the start location algoritm is used. If test(56) is 2, both grid search and start location algoritm is used.

User defined start location: If an S is written in the input S-file at column 45 of the epicenter line, the location starts at the location (epicenter) given on the header line. If an S is written in column 44 on header line, the depth iteration will start at depth given on the header line. If N is written in column 45, the nearest station will be used irrespective of global settings.

Starting depth:

If no event specific start depth is given in S-file, the starting depth is taken from the first number on the control line (see later) in the HYPO71 style. However, there is often problems obtaining a reliable depth due to local minima. This can be manually checked with program RMSDEP from EEV. HYP can also be set up to locate the same event starting with a range of different start depths, and then choose the one with the lowest RMS. This can significantly improve the reliability of depth determination. Selecting 3 to 5 different start depth is often enough. This option is set on the control line in the station file.

Fixing location:

Using F instead of S, fixes the position (depth and location).

Do not locate event:

If a * is written in column 45, the event is not located, can be used if an external location is to be kept unchanged.

Only calculate magntudes and update spectral values

Set TEST(106) to 1.0

Fixing origin time:

Using an F in column 11 of header line will fix the origin time given on the header line.

If both depth and location are fixed, but not the origin time, new origin time and residuals will be calculated. This can be useful when working with readings from a few stations which should be checked against known locations. If e.g. distant events are read, it is often the practice to put in the PDE location on the header line and calculate residuals relative to the observations. When the UPDATE is made, the agency of the location is NOT changed, assuming that if both depth and epicenter are fixed, the hypocenter must come from an external agency.