Fig. 6
The statistical occurrence of spatially averaged geoelectric field magnitudes. The averaging was carried out over the station groups shown in Fig. 1. The colors of the curves correspond to color coding of the groups in Fig. 1. Gray lines show the 3 and 8 V/km bounds for visually extrapolated statistics. The inset shows the return periods obtained from peaks over threshold analyses. The circle in the inset shows the largest spatially averaged magnitude in the data set. The box in the top right corner indicates the amount of data that were available for computing the statistics for each group