Suggestion: in orientation search, use cross-correlation normalised by Z power instead of CC coefficient

[ftilmann]

The title should say it all. The justification is given in Stachnik et al . (2012):

This function [Cross-correlation coefficient] is useful because it is bounded on the interval −1 to 1, but it is difficult to find a maximum because the autocorrelation of the radial component ($S_{rr}$ ) in the denominator varies with the numerator. This can result in a range of back azimuths with similar values near the maxi- mum. Thus a second normalization is used: $C_{z ̄r} = S{ z ̄r}/S_{zz}$ which has a well-defined maximum value and is used to select the appropriate azimuth

The flat tops he alludes to are quite obvious in Fig. 3 of the 2019 SRL paper. It's easy to see why: an idealised Rayleigh wave with zero energy on the transverse would lead to a rectangular function of cross-correlation coefficient as dependent on trial orientation angle, ie. CC coefficient would be either -1 and 1. Using the vertical component normalisation instead leads to a more sinusoidal curve with a more clearly defined maximum (if you just pick the maximum, you could also ignore the normalisation entirely).