At a theoretical level, it could be done with ropes. You don't need to wait for earthquakes. Setup two anchors on either side of a fault. String ropes betwee

At a theoretical level, it could be done with ropes. You don't need to wait for earthquakes. Setup two anchors on either side of a fault. String ropes between them. As the two plates slowly more, the stretching ropes can be tied to generators. Totally theoretical but, no new physics is required to extract energy from two slowly moving things.