Sometime in 1991, Seattle became more than a quintessentially livable city where the coffee was strong, the people were friendly and the plastic was recycled. The unleashing of bands like Nirvana and Pearl Jam beyond the Pacific Northwest transformed Seattle into an adjective inextricably linked to the word sound, a marketable life-style packaged in flannel and devoid of shampoo. What turns a city into a seminal music scene? Minneapolis, Minnesota, the home of proto-alternative rockers like the Replacements and Husker Du, had its moment a few years ago. So did Austin, Texas, ground zero for the Butthole Surfers; and Athens, Georgia, the birthplace of R.E.M. and the B-52s. One necessary ingredient they all share is a healthy slacker class. Like Seattle, they are home to large universities, and they have been able to support an infrastructure of mom-and-pop record shops, cutting-edge clubs, vintage- clothing stores and alternative newspapers. They are also far enough away from New York City and Los Angeles to consider themselves cool, and uncorporate enough to make room for the strikingly unconventional. A homegrown record label can make a huge difference too, like Seattle's Sub Pop, which produced Nirvana's early recordings. Ultimately, it's the big national labels that cash in on local sounds. Primed by their success with Seattle, the record companies are now grazing hungrily in college towns, those intrinsically hip places where collective shoe preference may run the narrow gamut from Birkenstocks to Doc Martens but ears are all wide open. The academic triangle of Chapel Hill, Raleigh and Durham, North Carolina, boasts popular alternative bands like Superchunk, not to mention a label, Mammoth Records. Jay Faires, founder of Mammoth, set up shop in the area quite simply because ''there are a lot of 18- to 22-year-olds who don't have much to do, who smoke a lot of pot and who eventually pick up a guitar.'' Record executives are also looking at Halifax, Nova Scotia, a five- college town with dozens of hometown bands, as well as Portland, Oregon -- Gus Van Sant-land and a grunge Mecca in the making. But formulas aren't foolproof. San Diego, with its proximity to L.A. and its image as a dumb blond of a city, would seem like an improbable locale for a thriving anti-Establishment culture. But in fact it has spawned bands with names like Rocket from the Crypt and rust; both have signed with major labels. Explains Kane (that's just Kane), president of Headhunter Records, a local label: ''There's a lot less attitude down here, people are less jaded, there's a freshness.'' Keep your eye on Toledo, Ohio.