Use nonlinloc with 1d model

[JuanJose9611]

Hi,

Is it possible to use nonlinloc with a 1d velocity model instead of a 3d model? If so, are there any parameters in the input control file that need to be changed to work with 1d instead of 3d models?

Juan

[alomax]

Hi Juan,

Yes, the basic running of NLL uses a 1D model. See https://github.com/alomax/NonLinLoc/blob/dev/nlloc_sample/run/nlloc_sample.in in the sample/tutorial https://github.com/alomax/NonLinLoc/tree/dev/nlloc_sample for control file specifications and running with a 1D model.

Best regards, Anthony

[JuanJose9611]

To run Nlloc and locate the events is it necessary to first run the program Time2EQ?

Juan

[alomax]

Hello Juan,

No, not at all. Time2EQ is a (not so easy to use!) separate tool for generating synthetic picks.

Anthony

[JuanJose9611]

I created my own control file to run a sample with my own .obs file.

The programs returns a message that says X amount of events where read and it finishes without warnings or errors however there are 0 located events.

Would it be possible for you to take a look at my file and see if there is something wrong with it?

Juan

[alomax]

Hello Juan,

A common reason for no events locating is that the LOCGRID is not contained within the travel-time grid (determined by VGGRID, if travel-times generated by Grid2Time). You can check for this case (and see if there are other problems) by setting CONTROL 3 ....

If this does not help, you are welcome to send your control file, but I may also need the observations and any other files that running NLLoc requires. If you do not want to post this information, you can send to alomaxfree.fr

Best regards,

Anthony

[JuanJose9611]

Hi,

After changing to CONTROL 3 I noticed that I set the offset values incorrectly (should have been 0). After properly selecting the origin now the program does locate the events, however, the events appear to be on a L shape near the pre-locations. I will attach the .obs and .in files. If you have some time please take a look. My guess is that i am not properly setting the grids, both for the model and for location.

test_location_run.zip

Juan

[alomax]

Hi Juan,

I took a quick look. The main problem was that the LOCGRID was not centered on the seismicity so the events were locating at the corner of the LOCGRID.

I made a few other changes to the control parameters, see my comments ### in test_runfile_ALomax.in.txt

Many of these changes are optional.

Most events have hypocenter at the top or bottom of the LOCGRID, this is probably due to a lack of depth constraint since the stations are along a line and all to the NE of the seismicity: One event inside the station network has reasonable depth and moderate depth constraint:

Anthony

[JuanJose9611]

How did you determine the values to properly center the grid?

Juan

[alomax]

As I do in general, I center the projection near the middle of the seismicity: TRANS AZIMUTHAL_EQUIDIST WGS-84 30.79 -116.39 0

And then make the LOCGRID LOCGRID 301 301 51 -75.0 -75.0 0.0 0.5 0.5 0.5 larger then the extent of the seismicity 300x, 300y * 0.5 km, and put the grid origin (SW corner) half of the grid width in -x and half the grid height in -y -75.0 -75.0:

Anthony

[JuanJose9611]

Thank you for answering my questions. Some of the located earthquakes show stripes, if i wanted better resolution should i modify the LOCGRID or the VGGRID?

Juan

[alomax]

Hi Juan, This type of gridding usually is due to configuration/search settings or limitations of the available data or stations. Please see the following comments: https://github.com/ut-beg-texnet/NonLinLoc/issues/52#issuecomment-2293097968 https://github.com/ut-beg-texnet/NonLinLoc/issues/17#issuecomment-1105120448 There may be others, this issue arises often!

Best regards, Anthony