Multiple earthquakes can occur at a location. There may be different reasons for this, and the reason can have significant implications.
Shocks (main shock, with multiple pre- and after shocks):
(1) These occur roughly at the same location.
(2) Shocks may precede a major event.
(3) Shocks may follow a major event.
Storm:
(1) The multiple earthquakes occur along a fault or plate boundary.
(2) The occurrence of the initial earthquake sets off a second further along the plate boundary usually at some distance.
(3) The second triggers a third and so on, as the plate boundary "unzips."
(4) The unzipping may happen quickly (in which case it looks like one earthquake) or over months or years.
Swarm
(1) Multiple earthquakes roughly at the same location.
(2) The location is often near a volcano.
(3) The earthquakes tend to be roughly equal in intensity (none stands out as being significantly greater than the other).
