Geophysicists analyzed the dynamics of the San Francisco Bay rift zone and processes related to the movement of the Pacific Plate. Based on this analysis, they proposed reasons for the rapid rifting that occurred approximately six to eight million years ago.
According to the study published in the journal Science, the acceleration of rifting at the opposite boundary of the vast Pacific Plate could have been caused by the formation of a double subduction system in the western part of the Pacific Ocean. The formation of this system, as noted in the paper, contributed to the spread of extensional stresses.