Earthquake Glossary - interplate coupling
Interplate coupling is the ability of a fault between two plates to lock and accumulate stress. Strong interplate coupling means that the fault is locked and capable of accumulating stress, whereas weak coupling means that the fault is unlocked or only capable of accumulating low stress.
The earthquakes (colored dots) in the middle of the continent are intraplate events. Thoes near the ocean boundary are at the boundary between two plates (interplate).