What is the relationship between seismic gaps and earthquakes?

a
A seismic gap is the area where an earthquake originates
b
A seismic gap is an area along a fault where few earthquakes have occurred recently but strong ones have occurred in the past.
c
A seismic gap is an area where numberous, close faults create earthquakes
d
A seismic gap occurs because the interior of Earth is not uniform and waves travel through Earth's core at different speeds