The Upper Transition From Seismic To Aseismic Faulting on Subduction Megathrusts

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Intellectual Merit: This research investigates the cause of the world's largest earthquakes, which occur along subduction plate boundaries. These "megathrust" earthquakes rupture sections of the plate boundary, but we still do not understand how the limits of these rupture patches are determined. Goals of the work are to identify reasons why some sections of subduction plate boundaries fail catastrophically in large earthquakes whereas other sections fail by aseismic creep. Identifying these processes is essential to understanding the seismic cycle and predicting the behavior of subduction zones on time scales relevant to tsunami generation and seismic hazard. The research tests two hypotheses for the up dip limit of the seismogenic zone using a complementary set of laboratory-based approaches that focus on (1) frictional properties, including the effect of lithification and consolidation state, clay mineralogy, effective stress, and drainage conditions on frictional constitutive properties; and (2) fluid transport properties between lithification and consolidation state, composition, permeability, and rheology. Samples from ocean drilling cores, exhumed faults, and synthetic fault gouge will be analyzed in carefully controlled laboratory experiments on natural and synthetic samples over P-T, fluid, mineralogical, cementation, and compaction conditions that span the stability transition. Experiments include friction measurements, consolidation tests, measurement of elastic properties and permeability to constrain elastic stiffness, and measurements of effective stress. Biaxial and frictional shear experiments will be carried out as will uniaxial deformation and flow through tests. Broader Impacts: This research has the potential for significant societal impact from an improved understanding of fault mechanics and earthquake physics including tsunami generation and seismic hazard assessment. The effort also complements the NSF IODP and MARGINS programs. The project will train two graduate students and four undergraduate students with the students also getting opportunities to present the results of their research at professional meetings.