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Séminaire de Yo Fukushima
14 September 2018 à 14 h 00 min - 15 h 00 min
Title: Extremely early recurrence of intraplate fault rupture following the 2011 Tohoku-oki earthquake
Intraplate earthquakes on a fault in the Earth’s upper crust commonly recur in thousand 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. 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 post-seismic 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 to recur in just 5.8 years. This study suggests a mechanism to explain observations of extreme temporal clustering in paleoseismic earthquake recurrence studies.