- Subduction Megathrust Activities and Their Tsunami Impact
The past couple of decades witnessed a revolutionary progress of offshore geophysical monitoring worldwide in capturing a variety of slip behaviour of shallow megathrusts. These observations help reveal the nature of strain accumulation toward future ruptures, pose questions on the physical conditions that control the slip mode, and guide geodynamics studies of earthquake and tsunami processes and regional geohazards. We strive to integrate onshore and offshore observations (e.g., terrestrial GNSS, seafloor GNSS/Acoustic, ocean bottom and borehole fluid pressure data) into numerical modelling to study fault activities, crustal deformation, and stress and rheology. We also seek opportunities to develop new offshore experiments.
Selected related publications:
Davis, E., T. Sun, M. Heesemann, K. Becker, and A. Schlesinger (2023), Long-Term offshore borehole fluid-pressure monitoring at the Northern Cascadia subduction zone and inferences regarding the state of megathrust locking. Geochemistry, Geophysics, Geosystems, 24, doi:10.1029/2023GC010910
Sun, T., and E. Davis (2022), Monitoring the 2021 Mw 8.2 Alaska earthquake by an offshore seismic and fluid pressure observation network and implications for ocean-crust dynamic coupling. Geochemistry, Geophysics, Geosystems, 23, doi:10.1029/2022GC010540
Carvajal, M., T. Sun, K. Wang, H. Luo, and Y. Zhu (2022), Evaluating the tsunamigenic potential of buried versus trench-breaching megathrust slip. Journal of Geophysical Research: Solid Earth, doi:10.1029/2021JB023722
Sun, T., E. Davis, K.Wang, and Y. Jiang (2017), Trench-breaching afterslip following deeper coseismic slip of the 2012 Mw 7.6 Costa Rica earthquake constrained by near-trench pressure and land-based geodetic observations, Earth and Planetary Science Letters, doi:10.1016/j.epsl.2017.09.021
Sun, T., K. Wang, T. Fujiwara, S. Kodaira, and J. He (2017), Large fault slip peaking at trench in the 2011 Tohoku-oki earthquake, Nature Communications, doi:10.1038/ncomms14044
Davis, E. E., H. Villinger, and T. Sun (2015), Slow and delayed deformation and uplift of the outermost subduction prism following ETS and seismogenic slip events beneath Nicoya Peninsula, Costa Rica, Earth and Planetary Science Letters, doi:10.1016/j.epsl.2014.11.015
- Coupled Deformation and Fluid Flow Processes at Subduction Zones
In the subduction outer forearc, rapid loading of high-porosity and fluid-rich sediment due to accretion or subduction commonly leads to compaction disequilibrium and fluid overpressure. Development of upper-plate faults and evolving permeability structures of the plate interface and the compacting sediment matrix all significantly impact fluid drainage. The resulting sediment physical properties and interstitial fluid pressure strongly affect megathrust slip. To study these interconnected processes, we develop numerical models constrained by field and laboratory measurements of the mechanical and hydrological properties of sediments, rocks, and faults. The acquired knowledge would enhance our understanding of the variability of the slip behaviour of global shallow megathrusts.
Selected related publications:
Sun, T., S. Ellis, and D. Saffer (2020), Coupled evolution of deformation, pore pressure, and fluid flow in shallow subduction forearcs, Journal of Geophysical Research: Solid Earth, doi:10.1029/2019JB019101
Sun, T., D. Saffer, and S. Ellis (2020), Mechanical and hydrological effects of seamount subduction on megathrust stress and slip, Nature Geoscience, doi:10.1038/s41561-020-0542-0
- Earthquake Cycle Deformation at Subduction Zones
We study subduction earthquake-cycle deformation in the viscoelastic Earth. In addition to coseismic deformation directly caused by earthquake ruptures, this also includes subsequent (postseismic) deformation caused by continuing creep (afterslip) of parts of the fault and viscoelastic relaxation of the earthquake-induced stresses, and interseismic (or preseismic with respect to the next earthquake) deformation associated with megathrust locking. Our most recent focus on this topic includes the rheological impact of the lithosphere-asthenosphere boundary (LAB). Many seismological and electromagnetic imaging studies suggest this boundary to be sharp and likely associated with ponding partial melts. Modelling studies in progress suggest that a weak (low-viscosity) LAB would significantly affect earthquake-cycle deformation and viscoelastic stress transfer.
Selected related publications:
Sun, T., K. Wang, and J. He (2024), Geodetic signature of a weak Lithosphere-Asthenosphere Boundary in postseismic deformation of large subduction earthquakes, Earth and Planetary Science Letters, 630, 118619, doi:10.1016/j.epsl.2024.118619
Sun, T., K. Wang, and J. He (2018), Crustal deformation following great subduction earthquakes controlled by earthquake size and mantle rheology, Journal of Geophysical Research: Solid Earth, doi:10.1029/2017JB015242
Wang, K., T. Sun, L. Brown, R. Hino, T. Iinuma, S. Kodaira, and T. Fujiwara, Learning from crustal deformation associated with the M=9 2011 Tohoku-oki earthquake (2018), Geosphere, Thematic Issue: Subduction from Top to Bottom II, doi:10.1130/GES01531.1
Sun, T. and K. Wang (2015), Viscoelastic relaxation following subduction earthquakes and its effects on afterslip determination, Journal of Geophysical Research: Solid Earth, doi:10.1002/2014JB011707
Sun, T., K. Wang, T. Iinuma, R. Hino, J. He, H. Fujimoto, M. Kido, Y. Osada, S. Muira, Y. Ohta, and Y. Hu (2014), Prevalence of viscoelastic relaxation after the 2011 Tohoku-oki earthquake, Nature, doi:10.1038/nature13778