On the evening of January 23, 1974, a magnitude 3.5 earthquake struck the Berwyn Mountains in north Wales simultaneously with reports of brilliant lights on the hillside. Local nurse Pat Evans drove toward the disturbance and observed a large glowing pulsating ball on the mountain. No aircraft wreckage was ever found despite an RAF search.

MoD files released by the National Archives in 2010 attributed the event to a combination of an earthquake and a bright meteor widely observed across Wales and northern England. The concurrent lights and impact sounds attracted claims of a crashed spacecraft, leading tabloids to dub it the 'Welsh Roswell.' Earthquake light, a documented phenomenon, may account for Pat Evans's observation.