Fig. 4

Tidal phase angle histograms for each tidal index in each of the five regions. For each region, the number of earthquakes \(N\) is shown at the top right (above panel c). The dashed line in each panel shows the average relative frequency, and the thick curve is the sine wave approximation with amplitude \({A}_{1}\) and peak phase angle \({\varphi }_{{\text{p}}}\). Cases with significant correlations (\(p<0.05\)) are framed in red