noun
mild earthquake; weak earthquake
Refers to an earthquake of low intensity, typically around seismic intensity 3 on the JMA scale, where most people feel shaking but damage is rare.
昨夜、関東地方で弱震が観測された。
A mild earthquake was observed in the Kanto region last night.
弱震では、棚の物が落ちることはほとんどない。
In a mild earthquake, items on shelves rarely fall.
軽震 is an older term for intensity 2, now replaced by 微震 in modern JMA classification.
Compound of 弱 (weak) and 震 (earthquake), following the pattern of other seismic intensity terms like 微震 and 強震.