Bala Fault

The Bala Fault is a SW-NE trending geological fault in Wales that extends offshore into Cardigan Bay. In the offshore area it is a major normal fault and forms the bounding structure to the Cardigan Bay Basin, with a fill including about 2500 m of Lias Group. Onshore, it is responsible for the lineament which runs through Bala and south of Cadair Idris to the coast at Tywyn. At its northeastern end it links to the similarly orientated Llanelidan Fault.

The fault is believed to have experienced two separate stages of movement. The horizons between the upper Carboniferous sequence and the underlying Jurassic sequence are parallel, so little rotational movement occurred during the first stage. The second stage of movement happened in the middle-to-late Jurassic period, when strong rotation happened, up to 24 degrees.