[obspy-users] obspy.signal.polarization

Joachim Wassermann jowa at geophysik.uni-muenchen.de
Sun Jun 3 12:14:10 CEST 2018


Dear Andre,

the estimation of the azimuth has a 180 deg ambiguity. What is done in 
the Flinn algorithm (covariance and SVD) is simply fitting a rotational 
ellipsoid to the particle motion data. By definition it is not clear 
which incidence angle (compression or dilatation for P or SV or SH) the 
ray is taking. Thus without knowing the quadrant of an earthquakes 
radiation pattern or the wave type you are looking at it is not possible 
to solve this. Same is true for odr based techniques...
So if you have extra knowledge you need to include this 'by hand' and 
correct for this.

Best Joachim


	


Am 25/05/2018|21 um 03:08 schrieb A:
> In;
>
> obspy.signal.polarization..particle_motion_odr
>
> and,
>
> obspy.signal.polarization.polarization_analysis
>
> why are azimuths limited to 0 to 180 deg? I'm confused on whats going 
> on here, and assumed I'm not understanding something. I'm plotting 
> particle motion azimuths for an event in the center of an array, but 
> since the azimuths wont cross 180, the particle motion looks incorrect 
> (e.g. not radial).
>
> E.g. I expect my NW station to have an azimuth of 135 degree, and my 
> SE station to have an azimuth of the 315 (assuming these azimuths are 
> CW from north).
>
> -andre
>
>
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    Dr. Joachim Wassermann

    Geophysikalisches Observatorium
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