Multiple-mainshock events and long-term seismogenesis in Italy and New Zealand

The phenomenon of the precursory scale increase (Psi), on which the three-stage faulting model of long-term seismogenesis is based, has previously been studied in relation to mainshock/aftershock events, and clusters of such events, in California, Greece, Japan, and New Zealand. The tectonic environments of the studied events have comprised subduction, continental collision, and continental transform. In Italy, the study is now extended to large multiplet-type events and to extensional tectonics. New Zealand provides further examples of large multiplets. The results show that multiplets, interpreted as multiple-mainshock events, are preceded by the same Psi-phenomenon as the types of event previously studied. Psi again provides estimates of the location, start time, and magnitude level of the multiplet. It is concluded that the long-term seismogenic process that explains previously studied occurrences of the Psi-phenomenon, occurs equally with multiplets, and in conditions of extensional tectonics.