Consider two lag bolts in the stud, and two supports using heavy duty toggle anchors into the drywall. The toggle anchors use 1/4" bolts, and you can use 1/4" or even 3/8" lag bolts into the stud. If you add up the pull out weight capacity of all four it's probably more than enough even with 3x or 4x safety factor.

Predrill lag holes and use proper washers.

If you can find a way to put in even more toggle bolts it will help.

Or use 1/2" backing boards as others have suggested. This is the absolute safest and you can still use toggle bolts and lag bolts as described above.

Edit... not sure what your TV bracket is built like, or how it anchors into the TV body itself, but I suspect that even during an earthquake it is more likely to cause the mounting to fail at the bracket-TV interface than at the wall-bracket interface, if you anchor the bracket to the wall correctly. I'm guessing the TV body is molded plastic. Maybe there's some aluminum, but maybe not.