Microearthquake

Japanese: 微小地震 - びしょうじしん（英語表記）microearthquake

A small earthquake that cannot be felt by the human body but can be detected by highly sensitive seismometers. In Japan, earthquakes with a magnitude ( M ) between 1 and 3 are called microearthquakes, and earthquakes with a magnitude of less than 1 are called ultra-microearthquakes. Earthquakes have a certain frequency distribution in which the larger the magnitude, the fewer there are, and the smaller the magnitude, the more there are, and this trend is the same for large earthquakes and microearthquakes in the same area. Therefore, by observing microearthquakes in a certain area, the trend of seismic activity in that area can be determined in a short period of time.

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

人体では感じないが，高感度地震計で検出されるような小さな地震。日本ではマグニチュード（M）1以上 3未満の地震を微小地震と呼び，M1未満の地震は極微小地震という。地震はマグニチュードの大きいものほど数が少なく，マグニチュードの小さいものほど数が多い，という一定の発生頻度分布があり，その傾向は同じ地域においては大きい地震でも微小地震でも変わらない。したがってある地域の微小地震の観測を行なえば，短期間でその地域の地震活動の傾向がわかる。

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