Times of increased probability of strong earthquakes (M ≥ 7.5) diagnosed by Algorithm M8 in Japan and adjacent territories

This paper continues to explore the possibility of identifying the times of increased probability (TIPs) of occurrence of a strong earthquake by premonitory intermediate-term seismic activation in lower-magnitude range, as defined in the algorithm M8. A TIP refers to a 5-year period and an area whose linear size is several times larger than that of an incipient earthquake. In the course of the global test of the algorithm we applied it retrospectively to the data from the National Earthquake Information Center worldwide earthquake catalog (since the regional Japan Meteorological Agency catalog was unavailable to authors), related to the segment of circum-Pacific belt between latitudes 20°N and 48°N, from the south of Kuril arc to the Taiwan and Izu-Bonin arc. The worldwide catalog allows us to diagnose TIPs for earthquakes above magnitude 7.5 from 1975 on. Five out of six earthquakes with M ≥ 7.5 occurred within the TIPs diagnosed by the algorithm M8 with a priori fixed parameters. The missed earthquake occurred at the final stage of formation of the corresponding TIP. Altogether, the TIPs occupy less than 20%, and times of expectation occupy about 8%, of the total space-time domain considered. There are also current TIPs covering about half of the territory. Application of the additional algorithm of localization, named “Mendocino Scenario,” indicates that the southern part of the Japan trench is an area deserving particular attention. The results obtained here by no means constitute the definitive earthquake prediction but merely outline the territories for more detailed and comprehensive analysis. If confirmed by regional data, the results may be used for implementation of some safety measures and evaluation of other precursors, including short-term ones.