余震

1. Origins, structure, and basic meaning

• Structure: 余震 is read as よしん and is a noun for an aftershock, a tremor that follows the main shock of an earthquake.
• Basic usage: Use 余震がおさまる for aftershocks subsiding and 余震を想定する for assuming one in a drill.

2. Common pitfalls and similar expressions

• Relation to the main shock
  • 余震 does not mean any tremor; it is an earthquake occurring after the main shock.
• Actual event versus assumption
  • がおさまる describes a real event subsiding, while を想定する frames it as a preparedness scenario.