What would be the environmental and economic consequences of a 7.6 magnitude earthquake in Rio Vista, CA?

Um... pretty much nobody would care unless they did direct business with someone in Rio Vista. Their only real industry is natural gas extraction. Considering modern building codes, materials, engineering, and so on, particularly the incredible strength that is built into extraction facilities... you'll have some lesser homes damaged, but people build natural gas wells to stand up to damage. It's in their economic interest to make sure that they don't lose any pumping time for repairs, or even just more than an hour of post-quake maintenance.

Rio Vista isn't anywhere near any major cities. It's pretty much smack in the middle of the wide open San Joaquin Delta between Fairfield, Antioch and Stockton. Besides the damage to the town itself I don't think even a 7.6'er would do much damage to the Valley or East bay.