User_Guide_FOCI

This application performs moment tensor inversion and determines the focal mechanisms of seismic events using the P-wave first arrivals from the waveforms recorded by the seismic stations.

The following files are necessary in order to perform the moment tensor inversion, as shown in Figure 1:

Using Seed Waveform. The User selects a Seed file from the Episode database, or after applying the ‘Signal Download Tool’ (Figure 2, see “Low Level Services” chapter).
Using Seismic Event. The User select a seismic event which has been downloaded after applying the ‘Signal Download Tool’ (Figure 2, see “Low Level Services” chapter).
Using Ray Tracing Angles. Ray tracing angles table uploaded from the selected Episode database (see "AH Episodes" chapter).

Figure 1.

Figure 2.

The FOCI application can be selected from the seed file as shown in Figure 2b:

Figure 2b.

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 3. 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 3, 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 3.

Figure 3.

Waveform Processing

The options provided by the waveform viewer are described in Figure 4: When clicking on one waveform, a detailed waveform window extends.

Figure 4.

The user selects the component(s) that he/she wishes to be displayed in the screen. East-West, North-South, Vertical.
Horizontal zooming in-out.
Vertical zooming in-out.
Undo all zooming.
Select between phase (start and end point) picking and single point picking.
Only P-wave is enabled in this Application. (In other Applications, selection between P-wave and S-wave picking are possible, see "Waveform viewer guide" in "Visualization" chapter).
Undo picking.
Horizontal zooming tool. The User may alternatively zoom in-out the waveform by clicking on this small vertical bar and move the mouse left-right. The User may also click and drag the selected (shaded) part of the waveform left and right.
Collapse the details of the waveform.
Move the selected (zoomed) part of the waveform left-right.

Picking Phase (also see "Waveform viewer guide" in "Visualization" chapter):

The User has to pick a starting and an ending point from the Vertical component of a station (**Z channel - see Figure 5). Then, he/she has to repeat this picking for the other stations.

NOTE: Although it is not necessary to pick P-wave arrivals in all of the waveforms to run the application, a minimum of 8 picks is required for the service to proceed to the calculations (stated also at the bottom of Figure 5). The number of the seismograms and P-wave phases picked, are updated, each time the User selects makes a new picking.

Figure 5.

Parameters selected for the waveform inversion:

For most of the additional parameters required to execute the service a brief description is already given on the screen (Figure 6).

Custom event depth [km]: The depth of the event is already taken from the catalog, however the User has here the chance to modify the given value, or retry the process with different depths.

Output file name: The User may select the name of the files that are going to be saved after the inversion process.

Density [kg/m³]: The density of the medium is requested by the user.

Select Output solution types: All options are described next to the boxes. The User may tick any of them he/she wishes, or select all of them by putting a tick in the box indicated by green color in Figure 6.

Advanced Options: (NOT IMPLEMENTED YET)

Figure 6.

When the picking and the parameter selection is over, the User shall click on "RUN" (blue button, bottom of Figure 6) to initiate the Moment Tensor Inversion.

The results obtained after the process terminates include the values of the parameters and also focal mechanism types, as requested in the previous step (Figure 6). An example is shown in Figure 7. The scheme of the focal mechanisms (.png files, red frame of Figure 7) can be demonstrated and downloaded by the User. Tables with numerical values (.asc files, red frame of Figure 7) can also be displayed on the screen.

Figure 7.