Good morning.
I'm trying to fix a proper velocity model for waveform inversion. I thought that if I get a good "rms" with the localisation I can start the inversion with that velocity model.
The thing is that I get a good rms (under 0.15) and an acceptable erh and erz (under 1km). The gap, the itr and the v1/v4 are also acceptable in all trials. But each time I get a different locations, far away with almost 5 km in some results.
How can we choose with certitude a proper velocity model when all trials give a good output parameter?
First of all, are all your earthquakes crustal ones ? If so, try to identify extra information available, like faults existing in the epicentral area. And see how the epicenters are matching the faults path. Maybe some Seismic Prospecting data or tectonic information are available too and could be compared to the obtained fault plane solutions too. Maybe some large refraction profiles are available in your area to fix the depth to Moho and so on. You may use other codes for joint hypocentral determination, like VELEST and see the results too.
To conclude, simply using some rms values is not enough and extra information should be used.
Thank you Marian Ivan for your explanation. I never used Velest, I should try it.
Maybe my question wasn't clear. I don't have different earthquakes. Only one single event, but I get different location using different velocity models. I'm confused which one to use when all results appear to be acceptable.
I used 4 models, one of them is from Seismic prospection wide angle data, and another from a seismic tomography study. The other two are using trial and error.
If you have a single event, your options are quite limited. Maybe only look for the faults in the area and accept the velocity model providing a location close to the major fault. If you obtained the focal mechanism, it could be also correlated to the type of the fault (i.e strike-slip or normal /inverse fault), if you know more about the tectonic settings there. Or maybe GPS velocities are available, or gravimetric measurements and so on to provide you some extra information.
VELEST can be used only if having a large number of earthquakes in the same area. Otherwise you can not discriminate between the velocities models only on a math (i.e. rms fit) base. The code you use for inversion is also important. Finally, search for the International Seismological Center Bulletin and for NEIC (US Geological Survey) location of your earthquake. Most likely, you will see various locations provided by different agencies because they use different velocities models, different inversion codes and, in some cases, different number of recording stations. Picking of the arrivals by different analysts can also provide slightly different values and so on. As you can see, the accurate location is not so simple as it looks to be. Good luck !
Thank you @Marian Ivan For this explanation.
I will double check with all the points you mentioned. This is very helpful. Thank you.
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Waves