4.1 SE Locator

SE has got a completely new interface for locating events in SEISAN version 11.0. While previously, location was done in a separate program, the location routine (still using HYP) has been integrated into SE. This makes it possible to get a more user friendly graphical output from the locater, which can stay open while other activities take place. The locater can be started in two ways:

From the main event list, location is still started with command 'l', and a new window pops up.

Plotting in MULPLT, multi trace mode,' l' can also be used as before, but now the locater window comes up.

Figure 4.20 shows an example

Figure 4.20: Example of locating an event, the locator window.

Main locator window

When the Locator window pops up, a location has already been made and the results of the location is shown. These results are the same as given when locating with EEV, however more results are shown than locating with EEV, where one has to look in the print.out file to see all results. The results are latitude, longitude, depth, origin time (all with errors). Dx(km), Dy(km), Dz (km) and Dot (sec) are the difference in location from previous solution in longitude, latitude, depth and origin time. The GAP and number of stations (NSt) are also shown. The upper right corner shows the magnitude/settings window, see below.

Update and event selection

The location, as shown in the locater window, must be saved (use button Save) in order for the results to saved in the data base (S-file). It is thus possible to do test without committing the results to the data base. In the Locator window, it is also possible to go to next and previous event without returning to the main window. However, when going to next event or previous event, no location is done and the data shown is taken from the S-file. Locate must be pressed to locate.

There is also an option for Save and Rename under File tab. This option will update the S-file name and the ID line to correspond to the origin time. Outside SE this can only be done with program UPDATE, see UPDATE to see why this is done. Option 'u' in EEV is not changing the filename and ID, only updating result in S-file.

Under the tab Edit, it is possible to copy the epicentre location to the paste buffer for use elsewhere.

Using the locater window as an editor

Several parameters in the locater window can be edited to facilitate simple changes and tests. Many of these fields are outlined with gray like the phases and the input phase weight. In addition, the following can be edited: latitude, longitude, depth, origin time, distance indicator and event indicator. The fix depth and fix epicentre flags can be set with tick boxes. More options are available in Settings seen in the magnitude box, see Figure 4.21

Figure 4.21: The options under Settings in the magnitude box.

Travel times and residuals

The residuals are color coded. The limits are hardwired and the intention is that they should be user settable in the next version. The limits are:

0.0-0.99 Green
1.0-1.99 Yellow
2.0-2.99 Orange
\bgroup\color{black}$>$\egroup3.0 Red

RMS is color coded in a similar way. If any problem with the phases, the name of the Phase shows an exclamation sign (!) as shown above. This is also the case with Magnitude and Azimuth tabs.

Abbreviations are: Stat: Station code, Comp: the two letter component code from S-file, Dist: epicentral distance in km, Azm: Azimuth, O: Onset (I, E or blank), PhObs: Phase observed, WtObs: Weight observed, blank or 0 means full weight, 1 is 0.75 , 2 is 0.5, 3 is 0.25, 4 is zero weight, 9 means using S-P (all are HYPO71 style weights), T-obs: Observed travel time, PhCal: Phase calculated (the one the program calculate as the fastest), Ain: Angle of incidence at the source, WtCal: Weight used by the program (from 0.0 to 1.0), T-cal: Travel time calculated, Res: Residual=T-Obs - T-Cal and Imp: Importance of phase in the solution calculated as a percentage, importance of all phases should add up to 100 Magnitudes

The average magnitudes are shown in the Locator window, upper right and corner. All magnitudes available for the event are shown so magnitudes on additional header lines are included. The magnitudes are sorted in importance as specified in parameter file SEISAN.DEF. The magnitudes not calculated by SEISAN are shown with less contrast than the magnitudes calculated by SEISAN. The 3. magnitude on the header line, which might not be calculated by SEISAN, is considered a SEISAN magnitude. This magnitude is often put in an external reliable reference magnitude. The magnitudes not calculated by SEISAN (not including 3. Magnitude) area t ten of the list.

For each magnitude calculated by SEISAN, it is possible to show the individual station magnitudes with the magnitude residual by pressing the Magnitude tab. See Figure 4.22.

Figure 4.22: The magnitude window with magnitudes per channel, corresponding input data and magnitude residuals.

The magnitude window show all the input used for calculating the magnitudes: Amplitude, period, coda and seismic moment (log value) as given in the S-file. Similar to the travel time residuals, the magnitude residuals are color coded in order to quickly find deviating magnitudes which could indicate bad readings or wrong calibration file. The limits are:

0.0-0.19 Green
0.2-0.39 Yellow
0.4-0.79 Orange
\bgroup\color{black}$>$\egroup0.8 Red

Additional abbreviations: MagType: Magnitude type, Amp: Amplitude (nm or nm/s), Coda: coda length(s), Moment: Log seismic moment (dyn cm) and Mag: Magnitude.

Azimuth (backazimuth)

If backazimuths are available, they can be seen in the Azimuth tab. See Figure 4.23

Figure 4.23: The Azimuth (backazimuth) tab.

In this tab, only the weight observed (WtObs) values can be edited. The residuals are color coded. The limits are:

0-5 Green
5-10 Yellow
10-20 Orange
\bgroup\color{black}$>$\egroup20 Red

Additional abbreviations: BazObs: backazimuth observed, AppVel: Apparent velocity (km/s) and BazCal: Calculated backazimuth.

Log tab

This tab will automatically come up if the location routine returns a message (like a missing station, errors in station file or if the event cannot be located). In the last case, it is often useful to check the print.out file to get an explanation for why the location was not possible.