The software processing the illustrative nationwide maps of figures 2 and 3 in Iervolino et al. (2015) was found to have a bug. The corrected figures are below (Figs. 1 and 2). None of the discussions or the conclusions of the study are affected by this error, yet the authors, who strive for the highest quality of their work, apologize.
- Manuscript received 4 December 2015.