Intermediate-term predictions of earthquakes in Italy: Algorithm M8

Large earthquakes in Italy are preceded by a specific seismic activation which could be diagnosed by a reproducible intermediate-term earthquake prediction method-a modification for lower seismic rate areas of the algorithm, known as M8 (KEILIS-BOROK, and KOSSOBOKOV, 1990). Use has been made of the PFG-ING catalog of earthquakes, compiled on a regular basis, to determine areas and times of increased probability for occurrences of M greater than or equal to 6 earthquakes. In retroactive simulation of forward prediction, for the period 1972-1995, both the 1976 Friuli, M = 6.1 and the 1980 Irpinia, M = 6.5 earthquakes are predicted. In the experiment where priority magnitude scale is used, the times of increased probability for a strong earthquake to occur (TIPs) occupy less than a quarter of the total magnitude-space-time domain, and are rather stable with respect to positioning of circles of investigation. Successful stability tests have been made considering a recently compiled catalog (CCl97) (PERESAN et nl., 1997). In combination with the CN algorithm results (COSTA ct al., 1996) the spatio-temporal uncertainty of the prediction could be reduced to 5%. The use of M8 for the forward prediction requires the computations to be repeated each half-year, using the updated catalog.