Two earthquake swarms on the Kermadec Ridge

Abstract Two earthquake swarms on the Kermadec Ridge, in April 1961 and January 1965, occurred in almost the same place, roughly 4° from the North Island coast. New Zealand seismograph stations recorded about 200 events of magnitude M L ≥ 4 in each swarm. The first swarm lasted 2.3 days and the second 13.5 days. The average values of b are: 1.50 ± 0.19 and 1.34 ± 0.20, respectively. The frequency‐magnitude relation varied during the course of the two swarms, but the patterns of changes are different. In the 1961 swarm, the variation in rate of occurrence has two stages, one similar to that in a foreshock sequence, and one like that in an aftershock sequence; the 1965 swarm followed the pattern typical of aftershocks.