Map showing the location of the quakes (blue squares) and the San Andreas Fault (red line) in the Gulf of Mexico. From the United States Geological Survey
The Gulf of Mexico is an extensional basin running along the southern part of the San Andreas Fault. The basin runs on-land as the Imperial Valley of Southern California; for this reason the southern part of the San Andreas Fault is sometimes known as the Imperial Fault. Extensional basins occur where two plates move apart from one-another, in this case the Pacific and North American. Potentially the Gulf of California could one day evolve into a new ocean, though this is not guaranteed, most extensional basins stop expanding before this happens.