Observed change in plate coupling close to the rupture initiation area before the occurrence of the 2011 Tohoku earthquake: Implications from an earthquake cycle model

Changes in plate coupling off the coast of Fukushima have been detected by GPS since 2000. These changes occurred close to the rupture initiation area of the Mw9.0 2011 Tohoku earthquake and possibly initiated the earthquake. We investigated these changes with quasi-dynamic earthquake cycle simulations using a hierarchical asperity model. We modeled the entire rupture region as rate weakening but conditionally stable, while areas with huge slips and Mw7 asperities were modeled as strong and ordinary rate-weakening unstable friction, respectively. The following observed characteristics were reproduced: long recurrence time, large rupture region (including a localized huge coseismic slip area and source area of recurring Mw7 earthquakes), and a Mw7 foreshock triggering the Tohoku earthquake. Off Fukushima, repeated aseismic slips propagating northward appeared in the last half of the cycle and possibly caused the decrease in plate coupling. However, it is not necessarily related to the immediate occurrence of the giant earthquake.