Dynamic Nankai Trough (Japan) & Middle America Trench (Costa Rica) Sediment Triaxial Experiments

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A large body of work has been carried out on the sedimentary dynamics and tectonic evolution of the earthquake-prone subduction zones off Japan and Costa Rica. This work suggests that excess pore pressures are closely linked to dehydration and fluid flow processes in the accreted and underthrust sediments. However, the study of the effects of transient pore pressure changes and mineralogical controls on sediment failure have so far been restricted to static deformation. As a consequence, dynamic effects such as cyclic loading or earthquake shaking could not be considered. On the other hand, increasing evidence suggests that especially cyclic loading of otherwise stable systems may trigger (hydraulic) failure. In this low-cost proposal, we propose to carry out laboratory tests using a1state-of-the-art laboratory technology to simulate earthquake tremor on pristine whole round (WR) samples recovered during OOP legs 170 and 190. The experimental strategy is two-fold: (i) We submit an aliquot of each sample similar confining stresses and cyclic loads to study differences in pore pressure evolution and failure, (ii) We then take seismic records from recent earthquakes in each area and submit the other aliquot of the same sample to these stresses under their pre-consolidation stresses (i.e. inferred in situ conditions). This will not only allow us to learn about the mechanical response, but some risk assessment concerning catastrophic failure. The study is carried out using a custom-built, one-of-a-kind dynamic (up to 50 Hz), computer-controlled triaxial shear apparatus recently developed at the Marine Geotechnics laboratory at RCOM Bremen.