In general, the earthquake catalogs include a lot of information about the seismic wave parameters related to the earthquake source, but they rarely include the polarity of P-waves although in most of the cases these catalogs include the value of the amplitude for the P-waves (Pg, Pn..) and S-waves (Sn). In general, the automatic focal mechanism solutions are provided for earthquakes with magnitudes greater than M5 and in a few cases, M4.5. I have been browsing the net to check different softwares and free codes provided by universities and geological services. Most of them are compiled in Fortran although they do not specify the range of value of the earthquake magnitude to obtain a nonsense solution. In this sense, I would like to obtain a feedback about researches which are working with small earthquakes (M
If you are familiar with Python, then I'd suggest having a look at the Obspy package for constructing an Event object and the HASHpy (https://github.com/markcwill/hashpy) lib. This is a Python port to the HASH software of Hardebeck & Shearer.
Here at the ROB, we use home-made fortran routines for P-wave polarity, or for P, SV and SH absolute amplitude (apparent moment) focal mechanisms calculations. We use those for events as low as ~1.5 if well recorded by a local network.
Refs:
Hardebeck, Jeanne L. and Peter M. Shearer, A new method for determining first- motion focal mechanisms, Bulletin of the Seismological Society of America, 92, 2264-2276, 2002.
Hardebeck, Jeanne L. and Peter M. Shearer, Using S/P Amplitude Ratios to Constrain the Focal Mechanisms of Small Earthquakes, Bulletin of the Seismological Society of America, 93, 2434-2444, 2003.
Dear Thomas
Thank you very much for your answer. Unfortunately I am not skilled in Python. I am searching some code in Matlab or Fortran. However, I am willing to introduce myself in the Python world.
Thank you again for your answer and references.
Cheers
Raul
Ouauuuu.. I have read the last paragraph regarding the calculation for sized events as low as 1.5.... I will try!!
regards
Dear Arun
Thank you for your answer, where I can get Seisan, is it freeware?
Best regards
Raul
It is entirely free.
http://www.uib.no/en/rg/geodyn/54592/software
Look for download at the bottom of the page.
Calculating focal mechanisms is one of the standard functions here and is all explained in the manual.
Christian
I have our own software, referred in:
De Natale G., Ferraro A. & Virieux J. (1991). A probability method for earthquake focal
mechanisms. Geophys. Res. Lett., 18 (4): 613-616.
Unqualified comment: The issues of earthquakes are no longer those of proverbial "earthquakes". They should be re-understood from the perspective of ways and means of energy storage in earth (and the rate) and its effects upon "initiation" of relaxation (and of course the rate in time-space and scale sense), if not redefined.
In very vague terms, or ideally, the earth may be treated as an extraordinary body of "defects" intelligent enough to attain a controlled relaxation or the best repose (within time and space at disposal) when stimulated beyond criticality.
In short the physics of initiation of primary ground motions (including modes conversions) and how they are amplified by "defects" complex of earth should be understood, in an optical behavior sense.
Locally both "control" and "isolation" strategies could be looked into, however, given all aspects are significantly understood.
Isolation appears plausible........
Unqualified comments (discussion continued) :
Those who are interested kindly muse the sense of
- Defect complex nature of terrestial faults in relation to "optical" type earthquake energy propagation behavior (link 1)
- How gravities of nature of sustained terrestrial gyration and celestial time-space position with variation thereof also tend a role in "repose" adjustment, whether friendly or unfriendly (link 2 with associated concepts)
1-https://www.upi.com/Science_News/2019/03/20/Supercomputer-simulation-details-Kaikoura-earthquakes-unusual-features/2991553091015/
2- https://www.upi.com/Science_News/2019/03/11/New-earthquaking-sensing-method-could-give-earlier-warnings/5581552272322/
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