Question

what eventually causes a release of stored energy at transform fault boundaries?

a decrease in temperature

plate fusion

overcoming the friction between plates

Explanation:

At transform fault boundaries, tectonic plates slide past each other horizontally. Friction between the plates initially holds them locked, storing elastic energy as they try to move. When the stress from plate motion exceeds this friction, the plates suddenly slip, releasing the stored energy (often as earthquakes). Temperature decrease and plate fusion are not mechanisms for energy release at transform faults.

Answer:

overcoming the friction between plates