A large transient event that may have led to the 2011 Tohoku earthquake is reported this week in Nature Communications. The authors calculate tectonic deformation along the Japan Trench subduction zone and show that, with slow deformation over 9 years, the event had a longer duration than any reported previously.
Transient events have been recognised at various subduction zones and have been implicated as the stressors associated with megathrust earthquakes, although the relationship remains elusive. Until now, no transient events had been reported at the Japan Trench, despite it being one of the most active subduction zones (tectonic plate boundaries where one plate moves beneath the other) in the world.
Kazuki Koketsu and colleagues used data from Global Positioning System stations to calculate the amount of deformation taking place along the trench over a 15-year period between 1996 and 2011. After removing the effects of nearby earthquakes from the data, the authors were able to simulate tectonic deformation and slip rates showing that a very long-term slow slip event occurred on the fault and may have triggered the Tohoku megathrust earthquake.
Although the research is not definitive, this is a step towards improving our understanding of these transient events and their relationship to large earthquakes. As our knowledge of the physics governing such deformation improves, it may inform earthquake early warning and rapid hazard response projects.