Distribution of displacement on and evolution of a young transform fault system: The northern San Andreas fault system, California

This paper presents a working model for the spatial and temporal distribution of dextral slip on the northern San Andreas fault system of coastal California, based primarily on field relations in the San Francisco Bay area, and offers insight into the evolution of a young transform fault system. A fundamental difference between this and previous models of slip distribution is that this model assigns negligible slip to the Pilarcitos fault, which has been suggested to have 120 to 250 +km of post early‐Miocene dextral slip, in previous models. Because separation on the San Francisco Peninsula reach of the San Andreas fault is about 25 km, and displacement on the San Andreas fault in central California is 310 to 320 km, more than 250 km of late Cenozoic dextral slip must be accommodated east of the San Francisco Peninsula. The distribution of this dextral slip is constrained by offset late Cenozoic and basement units. Slip distribution, combined with ages of offset features and plate boundary kinematic constraints, show that the distribution of slip rates on groups of faults along the transform boundary has changed in an irregular fashion through time, in contrast to existing models that propose progressive eastward migration of active faulting in the San Andreas system. In addition to the shifting patterns of displacement, a migrating transition zone connecting the eastern faults of the strike‐slip system to the Mendocino triple junction may have resulted in distributed dextral faulting and shortening in the northernmost and youngest part of the transform fault system.