Mechanically Coupled Areas on the Plate Interface in the Kanto Region, Central Japan, Generating Great Earthquakes and Slow-Slip Events

We detected the mechanically coupled areas, or high stress rate patches, on the plate interface in the Kanto region, central Japan, by analyzing the Global Navigation Satellite Systems data. The estimated patches correspond well with the focal areas of past great earthquakes and slow-slip events (Mw∼6.5) occurring every ∼5 yr. Using one of the estimated patches, we created a model of a slow-slip event as a stress release with a recurrence interval of 5 yr. This synthetic can reproduce observed features of the slow-slip events such as the slip distribution and the magnitude. We use the strain-energy magnitude Mw0 defined by the minimum strain-energy release to quantify the magnitude. This is useful to compare slow-slip events with ordinary earthquakes in terms of the strain energy release, whereas the moment magnitude does not represent the difference of the energy release in this case. The strain-energy magnitude of the slow-slip event was Mw0 4.9, which was considerably smaller than the moment magnitude, because the smaller stress drop of the slow-slip event results in a smaller strain-energy release. Furthermore, by assuming that stress has accumulated at the other patches corresponding to the source region of past earthquakes since the occurrence of the last earthquakes, we obtain a model of the stress accumulation in 2023. We then create various rupture scenarios of great earthquakes as combinations of ruptures of the different patches. When two or three of the patches release the accumulated stress simultaneously, an interplate earthquake with Mw≥7.8 can occur in the Kanto region.