SCEC NORCAT TAG: Northern California Cascadia-San Andreas Transition

Vera Schulte-Pelkum, Matthew Herman, Debi Kilb, Kathryn Materna, jason R. patton, David R. Shelly, & Amanda M. Thomas

Published August 2026, SCEC Contribution #15677

The Mendocino Triple Junction (MTJ), where the Cascadia Subduction Zone transitions into the San Andreas Fault system, is a structurally complex plate boundary region that remains understudied relative to its hazard importance. It is critically important for seismic hazard because it hosts both the tsunamigenic Cascadia megathrust and a transition to complex crustal strike-slip faulting capable of large, damaging earthquakes, with interactions between the two systems including possible partial synchronization. The one-day NORCAT workshop was held before the 2026 SCEC Annual Meeting primarily in person with a remote option. It convened investigators in seismology and paleoseismology, geodesy, tectonics, structural geology, and hazard communication, with the goal to synthesize current understanding and knowledge gaps and identify priority research directions. The program combined 15-minute invited talks with Q&A, 5-minute lightning talks, and a moderated discussion on the MTJ's tectonic evolution and structure. Presentations highlighted fundamental debates around first-order structure and associated processes, such as basic crustal fault geometry (San Andreas northern end) and plate configuration (e.g., position of the southern edge of the Gorda slab and extent of a slab window and/or a captured Pioneer fragment). New observations presented included machine learning-derived event catalogs, slow slip and tremor, lithospheric imaging, offshore fault imaging, kinematic reconstruction based on volcanics, LiDAR mapping, geodesy, community model viewers, rupture and earthquake cycle modeling studies, and disaster alert systems. Identified priorities include expanded onshore and offshore geodetic and seismic instrumentation, community three-dimensional visualization and cyberinfrastructure, and coordinated earthquake cycle simulations.

Citation
Schulte-Pelkum, V., Herman, M., Kilb, D., Materna, K., patton, j. R., Shelly, D. R., & Thomas, A. M. (2026, 08). SCEC NORCAT TAG: Northern California Cascadia-San Andreas Transition. Oral Presentation at 2026 SCEC Annual Meeting.