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Appendix A: Hypoinverse
lasOut, column 118, is the same as the remark in the code for duration on the phase
line, column 110, then the station magnitude is read and saved as part of the duration
magnitude. This code is set with the command FC1 in the Atlas.hyp file. If these
conditions are not met the duration pick will not be saved to the database.
The settings for the amplitude magnitude will also use the Eaton’s distance correction
as a default. This may be changed in the Atlas.hyp file using the LA0 command to
specify which channels use a different formulation. If the remark code in column 122
of the summary line in HypoAtlasOut matches the code in column 111 of the phase
line, then the station magnitude will be parsed and saved by Atlas. This code is set with
the command XC1 in the Atlas.hyp file.
A.3 How Atlas uses Hypoinverse
There are several avenues to locate an event. To locate interactively, press the locate
button on the toolbar or right click on a solution and choose locate. The contents of the
input file will be shown for editing, and the output of Hypoinverse will pop up in a separate window if these options are chosen. To turn either of these options on or off,
choose Tools > Customize – location, or use the checkbox options on the panels.
Hypoinverse is also called for all unlocated solutions in an event before saving to a
database; if hypoinverse fails, the solution is not saved. If no solutions are saved, the
event will be saved as an unlocated event. (See also Chapter 5.)
The main reason that hypoinverse would fail is not enough valid picks. To be valid, a
pick time must be within 6 minutes of all other pick times. The location of the stations
must be fairly close together. The DAM command sets the minimum distance of the second closest station. The default is 250km. This command is in the Atlas.hyp file.
The pick will also not be used by Hypoinverse if the station is not in the station file
defined by the STA command.
In addition to these restrictions, if the H71 command is set to 1 3 3, then the time and
location in the first line of the input file is used as the initial origin by Hypoinverse. The
arrival times must be within 6 minutes of the summary time and at least some station
locations must be within 250km of the trial origin (if the DAM command is left to
default). This precludes teleseismic events from being analyzed by Hypoinverse.
Lastly, Hypoinverse may fail if the format is not followed precisely. If the input file is
edited incorrectly, Hypoinverse may fail. Any failure will be reported in the output
screen. A failed attempt will not affect the solution in memory.
To locate an event, Atlas constructs an input file called HypoAtlasIn that gives
Hypoinverse an initial time and (possibly) initial location, as well as station phase and
magnitude information. The contents of this input file may be edited just before locating. Hypoinverse calculates the location and magnitude, then writes to a file called
HypoAtlasOut. Both input and output files are overwritten each time Hypoinverse
is called.
HypoAtlasIn starts with a summary line which holds an initial time and, if available, a location. The time is the current time of the event of the solution, or if not defined,
the time of the earliest pick. The location is left blank unless the previous solution con-
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Atlas Version 1.2
User Guide
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