Effect of seamount subduction on fault geometry and rupture propagation

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Dr. Christine Regalla has been awarded an NSF Earth Sciences Postdoctoral Fellowship to carry out a research and education plan while at McGill University in Montreal, Canada. She will investigate the role of variable fault geometry and strength in the vicinity of subducted seamounts on the nucleation and propagation of megathrust ruptures. This work has direct implications for understanding processes controlling the nucleation and maximum magnitude of large megathrust earthquakes. Subduction zones generate the world's largest earthquakes and tsunamis and the limits on earthquake size depend in part on the geometry of the fault boundary between the two plates. Rough spots and bumps such as seamounts on the down-going plate can affect the degree of locking along the plate boundary fault and modulate the magnitude and distribution of plate boundary slip during earthquakes. Results from this project can be applied to seismic hazard assessments to help estimate maximum rupture area and moment magnitude at megathrusts with subducted seamounts. This project will create opportunities for knowledge sharing between field and modeling-based research groups, and will provide valuable professional development for Regalla as an early-career scientist. In addition, this project will involve undergraduate student researchers, thereby providing opportunities for Regalla to develop educational and mentoring skills, and provide hands-on research opportunities for undergraduate students. Although the subduction of seamounts is common, there is considerable debate as to whether seamounts act as sites of earthquake nucleation or barriers that impede rupture propagation. This work will combine analyses of field outcrops of ancient plate boundary thrust faults that were active during seamount subduction with finite element models of dynamic rupture to evaluate proposed models of earthquake rupture. This project will provide the first known descriptions of the physical properties of the subduction thrust in locations where ancient seamounts have subducted to seismogenic depths, and will provide observationally-based model constraints for fault geometry and strength parameters in numeric simulations of rupture involving subducted seamounts. Results of this work will provide information on the structural accommodation of subducted seamounts and their control on earthquake rupture propagation.The fellowship is being co-funded with the Office of Integrated and International Activities - International Science and Engineering