A seismological term for a type of earthquake that releases energy gradually over hours or days, in contrast to typical sudden quakes. Often contrasted with ゆっくり地震 (slow earthquake) and 普通の地震 (ordinary earthquake).
See also: ゆっくり地震
Unlike ordinary earthquakes, slow earthquakes can cause shaking that lasts for a long time.
Researchers are trying to clarify the mechanism of slow earthquakes.