Earthquakes can happen almost anywhere, and one of the ways for finding a fault line is after the earthquake has occurred. Faults can be rather hard to find without prior indicators. One theory for oil is that it is made from microscopic life that has been pressured in sedimentary layers. This takes it some distance away from where the big earthquakes usually occur, which is along the major plate boundaries. The potential for oil to spill out in an earthquake is not that great, gas esp methane is more likely as it is closer to the surface and it does occur in earthquake prone areas.
In the past, earthquakes have destroyed small cities by erupting oil, one theory suggesting that this is what happened to Sodom and Gomorrah, based on the middle east in the past being prone to oil spilling out onto the surface.
It can happen naturally, though it is very unlikely now, and it has in the past, but not to this extent.