The earthquake was preceded by a small foreshock on the evening of 7 September.
From the en.wikipedia.org
Seismologists are calling this event a foreshock of the Friday earthquake.
From the cnn.com
Just in front of this bow wave lies a complex, turbulent system called the foreshock.
From the sciencedaily.com
After a foreshock, there is only a 5 percent chance of an even bigger quake coming later.
From the thenewstribune.com
This earthquake was preceded by a damaging foreshock on January 9th.
From the en.wikipedia.org
A strong foreshock preceded the mainshock by about 20 to 25 seconds.
From the en.wikipedia.org
For example, there is about a one in 20 chance that any quake is a foreshock of a large temblor.
From the sacbee.com
Lin noted that a sizeable foreshock preceded the Japan quake.
From the sciencedaily.com
The designation of an earthquake as foreshock, mainshock or aftershock is only possible after the event.
From the en.wikipedia.org
More examples
A tremor preceding an earthquake
An aftershock is a smaller earthquake that occurs after a previous large earthquake in the same area (the main shock). If an aftershock is larger than the main shock, the aftershock is redesignated as the main shock and the original main shock is redesignated as a foreshock. ...
(foreshocks) Smaller earthquakes preceding the main earthquake in a series.
A small tremor that commonly precedes a larger earthquake or main shock by seconds to weeks and that originates at or near the focus of the larger earthquake.