If you think the Southland’s earthquakes frighten enough people, think again. For the 16th year, Knott’s Berry Farm--renamed “Knott’s Scary Farm” for the season--opens its Halloween Haunt. Starting tonight, the Buena Park home of the boysenberry transforms itself after dark into a dimly lit haunting ground for a horde of witches, ghouls and slimy creatures. The tame Timber Mountain Log Ride becomes a toxic waste plant, oozing with bubbling poisons and terrorizing mutants. The Wilderness Dance Hall becomes death-filled rooms at the Bate’s Motel. And Bigfoot Rapids becomes the sacred burial ground of the legendary giant grizzly. This year, Elvira, “Mistress of the Dark,” returns to headline one of several shows. The macabre crew also includes 250 “extras” who invent their own horrific disguises (such as the one pictured) and audition for the jobs. Halloween Haunt--which has a three-weekend run and includes Halloween night--will lure at least 100,000 customers to Knott’s turnstiles during the promotion’s eight nights, said Stuart Zanville, park spokesman.