noun
initial response; first action
Used for the earliest actions taken in response to a crisis, disaster, or important event. Often appears in news and emergency contexts.
地震発生後の初動が被害の大きさを左右する。
The initial response after an earthquake determines the scale of the damage.
警察の初動捜査が事件解決の鍵となった
noun
preliminary tremor; initial shock
Specifically refers to the first detectable seismic wave or tremor before the main earthquake. Technical term used in seismology.
初動の波形から震源の位置を推定する。
The location of the epicenter is estimated from the waveform of the preliminary tremor.
The police's initial investigation was key to solving the case.