Tectonic corridors of the northern San Andreas plate boundary system: Developing a new framework crustal deformation model

Matthew Herman, & Kevin Furlong

Submitted September 7, 2025, SCEC Contribution #14843, 2025 SCEC Annual Meeting Poster #TBD

The northern San Andreas plate boundary represents the transformation of a subduction margin into a lithospheric scale transform boundary at the Mendocino triple junction. Recent analyses, including dense geodetic observations and a new high resolution seismic tomography image of the crust and mantle, combined with existing seismicity catalogs, fault maps, and other tectonic constraints, motivate us to develop an updated seismotectonic framework for this region. These combined observations lead us to a new framework model for northern California consisting of three crustal corridors: (i) the Salinian Corridor west of the San Andreas fault; (ii) the Pioneer Corridor between the San Andreas fault and the lithospheric-scale transform plate boundary that extends below the Maacama-Rodgers Creek-Hayward fault system; and (iii) the Mendocino Crustal Conveyor corridor east of the lithospheric-scale plate boundary, where slab window effects occur. A key feature of this model is a horizontal detachment extending across the Pioneer Corridor that separates shallow Franciscan crust (on the North America plate) from the Pioneer fragment, a remnant of the Farallon plate that moves northward with the Pacific plate. Further south, the detachment separates Franciscan crust from mafic material in the wake of the Pioneer fragment. Whether this detachment is seismogenic depends on a variety of properties including its kinematics, the temperature structure, and the associated rheology. Recent analyses of the 1906 San Francisco earthquake suggest it may have been seismogenically involved in that event. We are exploring the role of this crustal-scale structure on the seismic potential in northern California using a new 3-D deformation model for the San Andreas plate boundary that includes the horizontal detachment, as well as the other major fault structures in the region. With this model, we can investigate the patterns of inter-seismic loading and potential earthquake scenarios. One preliminary result from this ongoing work is that if the detachment is seismogenic and ruptures simultaneously with other regional crustal faults, slip on those features can be enhanced, including on the San Andreas and Maacama-Rodgers Creek-Hayward faults.

Key Words
San Andreas, Mendocino Triple Junction, Detachment, Faulting Model

Citation
Herman, M., & Furlong, K. (2025, 09). Tectonic corridors of the northern San Andreas plate boundary system: Developing a new framework crustal deformation model. Poster Presentation at 2025 SCEC Annual Meeting.

Related Projects & Working Groups
Plate Boundary System (PBS)