Intraplate earthquakes on a fault in Earth’s upper crust commonly recur in 1,000 years or longer. The 2011 M9 Tohoku-Oki earthquake triggered the activation of intraplate earthquakes in northern Kanto, Japan, including two M6 events on 19 March 2011 and 28 December 2016 located near one another. Here we use displacements captured by satellite radar and the Global Navigation Satellite System to show that the two earthquakes ruptured an identical fault. Detailed fault slip modelling shows that the deformation data for the two earthquakes are well explained by slip along a common fault geometry, and that the majority of the slipped area on the fault overlaps. Strain analysis reveals that the first M6 earthquake was followed by exceptionally large postseismic deformation. Such deformation is consistent with afterslip around the M6 rupture area, which in turn rebuilds the shear stress on the fault enabling the next earthquake. We infer that the rapid and large postseismic deformation of the 2011 Tohoku-Oki earthquake promoted such afterslip and made the second earthquake recur in just 5.8 years. This study suggests a mechanism to explain observations of extreme temporal clustering in palaeoseismic earthquake recurrence studies.