Fig. 7
Examples of directional analysis. The location of each example site is shown with a blue dot in Fig. 6. a Examples of rotated spectra between 0° and 80°. Grey and black lines are the instrumental x and y components, while blue and green lines identify the local longitudinal and transverse directions, at the selected rotation angle. b Frequency differences between resonance peaks observed along the instrumental x and y spectral components, for each rotation angle. The circles mark the angle(s) maximizing the frequency difference. c Spectral amplitude at the L0 frequency (marked by vertical grey line in panel a) estimated along the x or y component as indicated on each plot. The circles mark the selected angle \({\theta }_{s}\). d resulting longitudinal axis (blue line) for each example site at rotation angles corresponding to \({\theta }_{s}\) when the longitudinal direction is found on y instrumental component and to \({\theta }_{s}+90^\circ\) when it is found on the x component