The sudden jolt or shaking produced by an earthquake or underground explosion; a seismic shock wave.
Compound of 'earth' (Old English eorthe) and 'shock' (from Old French choc, possibly from Germanic). Became standard terminology in seismology and geology in the late 19th century.
Before seismographs, 'earthshock' was the only way to describe what your body felt—modern instruments turned something invisible into visible waves, transforming fear into data.
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