Fig. 3

Rotation angle θ dependence of (a) average Y/X amplitude spectral ratio and (b) D1 (red circles) and D2 (black circles) values obtained for station N.S6N14. Red and thin black curves in a represent amplitude spectral ratios for θ = 0° and other rotation angles (–40°––10°, 10°–40°), respectively. Red dotted curves are logarithmic standard deviation of the Y/X amplitude spectral ratio for θ = 0°