#earth_tremor__earthtremor__tremor__microseism  a small earthquake
  supertype:  earthquake__quake__temblor__seism  shaking and vibration at the surface of the earth resulting from underground movement along a fault plane of from volcanic activity
  subtype:  aftershock  a tremor (or one of a series of tremors) occurring after the main shock of an earthquake
  subtype:  foreshock  a tremor preceding an earthquake

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