Long-term premonitory seismicity patterns in Italy

The clustering of earthquakes as a premonition to a strong earthquake in the same region is defined as pattern BG, which is a generalization of patterns B (‘burst of aftershocks’) and S (‘swarm’), described previously (Caputo et al.; Keilis-Borok et al.); five out of the seven strongest earthquakes in Italy (M± 6.3, 1900–1980) are preceded by pattern BG within 5 yr; and eight out of 11 patterns BG are followed by a strong earthquake within 5 yr; the last pattern BG (1979 November 11) was diagnosed in advance of the Irpinia earthquake of 1980 November 23 (M=6.5). The statistical significance of pattern BG cannot be tested with the data on Italy alone.