Excerpt from article linked below:

In Japan, Professor Mogi noticed that large earthquakes tended to occur in the center of a peculiar doughnut-shaped pattern that developed in the ten or so years preceding the earthquake. The pattern involved an abnormal seismic calm in the hole of the doughnut and more than usual activity in the outer ring. Professor Mogi suggested that this pattern meant that the central region would undergo high stress and therefore be likely to have a large earthquake.

• Mogi Donut - Alaska Science Forum