* Gradual movement: Some faults slip gradually, without causing any noticeable shaking. This is called creep. Creep is common along faults that are located in areas with high levels of heat and pressure, such as near volcanoes or deep in the Earth's crust.

* Small movement: Some faults may only move a few millimeters or centimeters at a time. These small movements are not large enough to generate seismic waves that can be felt at the surface.

* Rock type: The type of rock that makes up a fault can also affect whether or not it produces earthquakes. Some rocks, such as granite, are more brittle than others, such as shale. Brittle rocks are more likely to break suddenly and generate seismic waves.

In order to produce an earthquake, movement along a fault must be sudden and large enough to generate seismic waves. The amount of movement required to generate an earthquake varies depending on the size and type of fault.