At 12.5 Ma, after subduction below the North American plate stops, right-lateral transform motion occurs along the margin between the Pacific and North American plates. The Tosco-Abreojos fault zone, located along the western margin of southern Baja California, has been interpreted as the main transform boundary between both plates until early Pliocene, when the plate boundary was transferred to the Gulf of California, leading to the capture of Baja California Peninsula by the Pacific plate. However, the morphology and the seismic activity of the Tosco-Abreojos fault zone suggest this right-lateral strike-slip motion is still active. The Tosco-Abreojos fault zone is characterized by bathymetric scarps and asymmetric basins filled by recent sediments which are deformed. These observations are compatible with the hypothesis that the motion of the Pacific plate with respect to the North American plate is partitioned, as indicated by kinematic data (GPS versus global models) between the still active Tosco-Abreojos fault zone and the Gulf of California where most of the motion is accommodated. The Baja California Peninsula can thus be considered as an independent block limited to the west by the Tosco-Abreojos and San Benito fault zones and to the east by the Gulf of California transform boundary.

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