It's the Hayward Fault, and it's nearly as major as they get. The fault runs end zone to endzone, so visiting teams expecting an earthquake should keep that in mind. Depending on which end of the field you're on, adjust your running plays accordingly. The west side of the field is going to get moved.
oh yeah....i stand corrected.....hayward is a major on for sure......i wonder since it slides off if and when it goes off it actually does much ......last time that went off to my knowledge was in the 80's cause I was going to Cal State Hayward at the time and we all ran down to the basement of science building to watch the seismagraph