User_Guide_Source_Location

This service performs inversion of seismic ﬁrst arrival time onsets, providing various hypocenter location estimations together with an advanced analysis of location uncertainties.

The following files are necessary in order to perform the source location, as shown in Figure 1:

Using Velocity Model. Velocity model uploaded from the Geological data of the selected Episode (see "AH Episodes" chapter).
Using Seismic Event. The User select a seismic event which has been downloaded after applying the ‘Signal Download Tool’ (see “Low Level Services” chapter).
Using Seed Waveform. The User selects a Seed file from the Episode database, or after applying the ‘Signal Download Tool’ (see “Low Level Services” chapter).
Using Catalog: The user may click on "change input" button in order to select the appropriate seismic catalog among the ones that are already uploaded in his/hers personal workspace.

Now, all data needed is available for the TRMLOC application.

Figure 1.

Once all these files are selected, a map appears on the screen showing the epicenter of the selected event (red circle) and the locations of the seismic stations comprising the regional network (green triangles), as demonstrated in figure 2. Information on the event and the stations appears on the screen, after clicking on the circle or the triangles, respectively. Moreover, the waveforms are also shown in the screen and are available for elaboration (see also Waveform viewer guide" in "Visualization" chapter). As depicted in Figure 2, only the vertical channels are shown by default, since the methodology applied in this service uses only P-waves. Nevertheless, the User can make all the channels appear on the window, by ticking the "E" and "N" components, next to the "Show channels" field, just below the map in Figure 2.

Figure 2.

In this service the User has to pick a single point in each waveform (Figure 2), instead of a phase (i.e. two points, starting and ending). For the waveform processing details see also “FOCI” and “Spectral Analysis” chapters.

Parameters selected for the source localization:

The additional input parameters required to execute the service are shown in Figure 3. Some of those parameters take numerical arguments, printed by the User, others take values selected from a list. In any case default values are provided. Advanced options are also available, however the service runs properly even if they are discarded. For detailed description of all service parameters please see at the trmloc manual at the document repository (link….)

Figure 3.

Once the point picking in the waveforms and the parameter selection is over, the User shall click on "RUN" (green button, left bottom corner of Figure 3) to initiate the Source Localization process.

The results obtained after the process terminates include a variety of output values, files and figures (Figs …). Numerical outputs are the hypocenter coordinates obtained by different methods, their uncertainties and the original coordinates from the catalog, for comparison (Figure 4, top). These values are also plotted in charts, one showing the epicentral location (longitude-latitude) of the original and obtained solutions together with the stations positions (Figure 4, bottom), and one more showing the vertical (depth) distribution of the aforementioned solutions. Four ascii files are also created (log.txt, res.txt, xcp.txt, and out.txt), which contained detailed and specialized information on the process, the results and their uncertainties (see trmloc manual for details, at the document repository - link). These files can be either displayed in the screen or downloaded by the User.