A magnitude 7.2 earthquake shook much of the North Island on Friday. Photo: GeoNet GNS Science experts are researching the relationship between them and the even bigger sea-floor quakes of magnitude 7.4 and 8.1 which hit the Kermadec Islands - 1000km - later on Friday morning. Seismologist Matt Gerstenberger said there are questions about whether the East Cape jolt was a single rupture - or something more complicated. Dr Gerstenberger said generally after a large earthquake a lot of quakes of varying size can be expected, but over time they become fewer and smaller. But he warned there is still an increased probability of a bigger event.