Fig. 1From: Characteristics of foreshock activity inferred from the JMA earthquake catalogJMA unified catalog for 20 years starting in October 1997. a Epicentral distribution (October 1, 1997, to July 25, 2017, M ≥ 1). Gray dots indicate epicenters in the inland area (depth ≤ 30 km). Red stars indicate M ≥ 7 earthquakes (also shown as A, B, C, and D). b Frequency–time diagram by month. The blue, yellow, and red bars indicate the entire magnitude, M ≥ 1, and M ≥ 2, respectivelyBack to article page