1) Earth tremor 2) Microseism 3) Minor earth tremor 4) Tremor 1) Tremor 
An earthquake that is smaller than, and precedes, a "mainshock". Foreshocks tend to occur in the same area as the mainshock. Foreshocks have not been observed before damaging earthquakes in British Columbia.
A foreshock is an earthquake that occurs before a larger seismic event (the mainshock) and is related to it in both time and space. The designation of an earthquake as foreshock, mainshock or aftershock is only possible after the full sequence of events has happened. ==Occurrence== Foreshock activity has been detected for about 40% of all moderate...
A minor, barely detectable earthquake, generally preceding a full-scale earthquake with approximately the same focus. Major quakes may follow a cluster of foreshocks by as little as a few seconds or as much as several weeks.
Small earth tremors that occur seconds to weeks before a significant earthquake event.
[n] - a tremor preceding an earthquake
noun a tremor preceding an earthquake
A minor tremor that precedes an earthquake. An increase in seismicity may signal that a major release of strain energy is about to occur.
A small earthquake that may precede a larger earthquake or main shock and that originates at or near the focus of the larger event.
a relatively small earthquake that precedes a greater one by a few days or weeks and originates at or near the focus of the larger earthquake.