Disentangling on-fault and off-fault contributions to geodetic strain rates in California

Nicolas Castro Perdomo, & Kaj M. Johnson

Submitted September 7, 2025, SCEC Contribution #14682, 2025 SCEC Annual Meeting Poster #TBD

Disentangling on-fault and off-fault contributions to geodetic strain rates is fundamental for earthquake hazard assessment but remains challenging. Here, we present a method that jointly estimates slip deficit rates on 3D faults and distributed moment rate sources in the crust, resolving the magnitude, style, and uncertainty of both components. Our model reveals that a significant share of interseismic deformation in California is accommodated off-fault, especially in regions of diffuse faulting. In localized fault systems such as the San Andreas, 75–90% of surface deformation is explained by fault coupling, whereas in the Eastern California Shear Zone, fault coupling accounts for only 60–70%, with the remainder off-fault. These findings highlight the critical role of distributed deformation in shaping interseismic strain rates and the need to incorporate off-fault processes into earthquake hazard models.

Key Words
Off-fault deformation, slip deficit rates, strain rates

Citation
Castro Perdomo, N., & Johnson, K. M. (2025, 09). Disentangling on-fault and off-fault contributions to geodetic strain rates in California. Poster Presentation at 2025 SCEC Annual Meeting.

Related Projects & Working Groups
Tectonic Geodesy