Last updated on August 12th 2016.

Note

The following links shows the example project as it should be just before step 2. You can use this to check your progress or restart the tutorial at this very point.

3. Seismic Events¶

Once the domain has been adjusted to your needs, you need to tell LASIF which events you want to use for the inversion. This works by simply placing a valid QuakeML 1.2 file at the correct location.

All events have to be stored in the EVENTS subfolder of the project. They have to be QuakeML 1.2 files with full moment tensor information.

LASIF provides some convenience methods for this purpose. One can make use of the IRIS SPUD service to get GlobalCMT events. Simply search for an event on their webpage and copy the event url. The lasif add_spud_event command will then grab the QuakeML file from the url and store an XML file in the correct folder.

$ lasif add_spud_event http://www.iris.edu/spud/momenttensor/835040
$ lasif add_spud_event http://www.iris.edu/spud/momenttensor/912955

These commands will download two event files and store them in the EVENTS subfolder.

$ ls EVENTS

GCMT_event_NORTHERN_ITALY_Mag_4.9_2000-8-21-17.xml
GCMT_event_NORTHWESTERN_BALKAN_REGION_Mag_5.9_1980-5-18-20.xml

A more convenient way to see which events are currently defined in the project is the lasif list_events command.

$ lasif list_events

2 events in project:
+------------------------------------------------------------+-----------------------------+
| Event Name                                                 |    Lat/Lng/Depth(km)/Mag    |
+------------------------------------------------------------+-----------------------------+
| GCMT_event_NORTHERN_ITALY_Mag_4.9_2000-8-21-17             |   44.9 /    8.5 /  15 / 4.9 |
| GCMT_event_NORTHWESTERN_BALKAN_REGION_Mag_5.9_1980-5-18-20 |   43.4 /   21.4 /  10 / 5.9 |
+------------------------------------------------------------+-----------------------------+

You will notice that events are identified via their filename minus the extension. This is an easy and flexible solution enabling you to tag the events as you see fit. The slight disadvantage of this approach is that you must not change the event filenames after you have worked with them because all additional information for that event will be related to it via the event filename. So please give them a good and reasonable filename. If you really feel that event renaming is a necessary feature please file an issue on Github so that the authors can add a proper event renaming function.

The lasif plot_events command will show a map with all events currently part of the project. With the same command, you can get histograms of depth distribution and origin time distribution by appending --type depth or --type time, respectively.

$ lasif plot_events

(Source code, png, hires.png, pdf)

The lasif event_info command is your friend if you want more information about a certain event:

$ lasif event_info GCMT_event_NORTHERN_ITALY_Mag_4.9_2000-8-21-17

Earthquake with 4.9 Mwc at NORTHERN ITALY
    Latitude: 44.870, Longitude: 8.480, Depth: 15.0 km
    2000-08-21T17:14:31.100000Z UTC

Station and waveform information available at 0 stations. Use '-v' to print them.

The information given with this command will be what LASIF uses. This is useful if the event has more than one origin and you want to know which one is actually used by LASIF. Notice that the event currently has no data associated with it. We will fix this in the next section.

3.1. Automatic Event Selection¶

Selecting events becomes tedious when selecting a larger number of events. Thus LASIF comes with an automatic routine to select events from the GCMT catalog, the lasif add_gcmt_events command. Arguments are number of events to select, minimum magnitude, maximum magnitude, and the minimum distance between two events in kilometers. See its help method for more details.

It will select events in an optimally distributed fashion by successively adding events that have the largest distance to the next closest station, approximating a Poisson disc distribution.

$ lasif add_gcmt_events 40 5 6.5 10

LASIF currently contains GCMT data from 2005 to 2016/2.
...
Selected 40 events.
Written EVENTS/GCMT_event_...
...

Note

You do not need to add all events you plan to use in the inversion at the beginning. Only add those you want to use for the very first inversion. LASIF is rather flexible and enables you to use different events, data, weighting schemes, etc. for every iteration. It will keep track of what actually happened during each iteration so the project gains reproducibility and provenance.