Impact of surface loading on stress and seismicity modulation in global subduction zones
Doctoral thesis, 2026
Surface mass redistribution from hydrological, atmospheric, and oceanic processes continually deforms the solid Earth and produces stress perturbations that are small in amplitude but coherent in space and periodic in time. This thesis examines whether such loading-induced stress variations are mechanically relevant for earthquake occurrence in subduction zones, and evaluates them in a tectonic context.
The regional study of the Kuril Islands-Japan region resolves loading-induced stress changes onto the megathrust geometry to compute monthly Coulomb failure stress changes from hydrological, atmospheric, and non-tidal ocean loading. A weak but statistically significant correlation is found between multi-loading-induced Coulomb stress variations and seismicity in some areas, with the clearest signal in the shallow southern Kuril segment near Hokkaido. The global study uses satellite gravimetry data from the GRACE and GRACE-FO missions to compute monthly loading-induced stress variations in the upper 50 km, and projects them onto principal tectonic stress directions inferred from earthquake focal mechanisms. The projected stress perturbations are then compared with background seismicity. Results reveal faulting- and region-dependent patterns of stress modulation and seismic response across global subduction zones.
Together, the results indicate that modest, periodic stress variations from surface loading can measurably modulate earthquake occurrence in parts of the subduction system, and that both fault-geometry-based and ambient-stress-based perspectives are useful for interpreting this modulation.
The regional study of the Kuril Islands-Japan region resolves loading-induced stress changes onto the megathrust geometry to compute monthly Coulomb failure stress changes from hydrological, atmospheric, and non-tidal ocean loading. A weak but statistically significant correlation is found between multi-loading-induced Coulomb stress variations and seismicity in some areas, with the clearest signal in the shallow southern Kuril segment near Hokkaido. The global study uses satellite gravimetry data from the GRACE and GRACE-FO missions to compute monthly loading-induced stress variations in the upper 50 km, and projects them onto principal tectonic stress directions inferred from earthquake focal mechanisms. The projected stress perturbations are then compared with background seismicity. Results reveal faulting- and region-dependent patterns of stress modulation and seismic response across global subduction zones.
Together, the results indicate that modest, periodic stress variations from surface loading can measurably modulate earthquake occurrence in parts of the subduction system, and that both fault-geometry-based and ambient-stress-based perspectives are useful for interpreting this modulation.
tectonic stress
Surface loading
seismicity
subduction zone
EF, EDIT-huset, Hörsalsvägen 11, Chalmers
Opponent: Hilary Martens, Associate Professor in Geophysics, University of Montana, USA
Author
Yiting Cai
Chalmers, Space, Earth and Environment, Onsala Space Observatory
Earthquakes are mainly driven by tectonic forces, but they can also be influenced by much smaller stresses caused by the movement of water, air, and ocean mass at Earth’s surface. This thesis examines whether cyclic surface loading can affect when earthquakes happen in subduction zones, where some of the world’s largest earthquakes occur. Using satellite gravity data and earthquake observations, the work tests how these repeating surface loads change stress in the crust and whether earthquake activity varies with them. A case study from the Japan region shows a weak but statistically significant link between loading-related stress changes and seismicity. A global analysis of subduction zones shows that the effect is not the same everywhere, but depends on regional conditions and faulting style. The results suggest that small, seasonal surface loads can help modulate earthquake occurrence in some places. This improves our understanding of how close faults are to failure and can support future studies of earthquake processes and hazards.
Subject Categories (SSIF 2025)
Geophysics
Earth Observation
Roots
Basic sciences
Infrastructure
Onsala Space Observatory
Chalmers e-Commons (incl. C3SE, 2020-)
DOI
10.63959/chalmers.dt/5870
ISBN
978-91-8103-413-4
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5870
Publisher
Chalmers
EF, EDIT-huset, Hörsalsvägen 11, Chalmers
Opponent: Hilary Martens, Associate Professor in Geophysics, University of Montana, USA