SCEC Award Number 26083 View PDF
Proposal Category Community Workshop
Proposal Title Northern California Cascadia-San Andreas Transition (NORCAT)
Investigator(s)
Name Organization
Vera Schulte-Pelkum University of Colorado, Boulder Debi Kilb University of California, San Diego Matthew Herman California State University, Bakersfield Kathryn Materna University of Colorado, Boulder
SCEC Objectives OBJ-01, OBJ-02, OBJ-07 SCEC Groups PBS, Seismology, CEM
Report Due Date 09/29/2026 Date Report Submitted 09/29/2026
Project Abstract
 The Mendocino Triple Junction (MTJ), where the Cascadia Subduction Zone transitions into the San Andreas Fault system (Fig. 1), 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.
SCEC Community Models Used Community Fault Model (CFM), Community Velocity Model (CVM), Community Rheology Model (CRM)
Usage Description The CFM, CVM, and CRM (including its geological framework) were used to put new observations in the 3-dimensional context of the current community models.
Intellectual Merit Resolution of the structure and earthquake behavior of the Mendocino Triple Junction, a plate boundary transition now within SCEC's scope, advances SCEC objectives OBJ-01, OBJ-02, and OBJ-07. The workshop synthesized new data sets and observations from machine learning earthquake catalogs, seismic imaging, geodesy, finite fault models, geology and volcanics, and others. By convening researchers across seismology, geodesy, tectonics, and hazard communication across a crucial juncture between the SCEC and CRESCENT focus regions, the workshop generated original synthesis, built the cross-disciplinary foundation to advance the MTJ as a priority region for SCEC earthquake cycle science, and bridged to CRESCENT activities.
Broader Impacts This workshop broadened participation in SCEC science, drawing in a number of researchers (including early-career scientists and students) who had not previously engaged with the region or with SCEC. Lightning talks featured graduate student and early career results, providing training and presentation experience. CRESCENT and SCEC co-hosted the workshop, building and strengthening connections between the two organizations. By convening federal (USGS, Cal OES, NSF) and academic partners around shared datasets and research questions, the workshop strengthened research and community safety infrastructure.
Project Participants Participants in this workshop included 7 workshop conveners, the SCEC director and an NSF program manager, 12 invited speakers, 8 lightning talks speakers, 4 remote participants, and 15 early career attendees. A total of 48 participants attended the workshop. Participants represented federal agencies (USGS, NSF), academia, state agencies (California Geological Survey, Cal OES), and nonprofits. 14 participants received travel support from SCEC, 7 from CRESCENT.
Exemplary Figure Figure 1: Map of Mendocino triple junction region. Dots are depth-colored seismicity from a machine learning seismicity catalog (Rong et al., 2025). Stars are low frequency earthquakes (Shelly et al., 2026). Colored lines show the southern edge of the subducting Gorda slab from a range of published studies. CSZ-Cascadia subduction zone trench; MF-Mendocino fault; SAF-San Andreas fault; Mc-Maacama fault; BSF-Bartlett Springs fault; plate boundaries with bolded labels from McPherson et al. (2025) and Prentice et al. (1999).
Linked Publications

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