Investigating Forearc Strength by Triaxial Testing of Marine Sediments from the Costa Rica Seismogenesis Project (IODP Expeditions 334 and 344)

Abstract:

Forearc stability and inherent tectonic failure processes at active continental margins very much depend on the strength of the composing sediments. Forearc sediments can either be prone to fracturing and more localized deformation or alternatively to creep and distributed deformation. Strength and deformation behavior can vary significantly depending on small differences in composition and fabric of the sediments as has been shown in a similar study on samples from the Nankai trench and forearc (Stipp et al., 2013). Cylindrical core samples with diameters of 30 and 50 mm recovered during IODP Expeditions 334 and 344 from a depth range of 7–788 m below sea floor were experimentally deformed in two different triaxial deformation apparatus under consolidated and undrained conditions at confining pressures of 0.4–20 MPa, room temperature, variable axial displacement rates of ~0.01–0.5 mm/min, and up to axial compressive strains of ~50%. Experimental results show great differences in the consolidation state and the related mechanical behavior of upper plate and incoming plate sediments. Similar to previous findings from the Nankai trench and forearc, structurally weak and structurally strong samples can be distinguished. One sample from shallow depth in the incoming plate shows a transition from structurally strong to structurally weak behavior with increasing confining pressure that has not been observed for Nankai samples. The differences in mechanical behavior may be the key for strain localization, faulting and surface breakage at active erosive as well as accretionary continental margins.

Reference: Stipp, M., Rolfs, M., Kitamura, Y., Behrmann, J.H., Schumann, K., Schulte-Kortnack, D. and Feeser, V. (2013). – Geochemistry, Geophysics, Geosystems 14/11, doi: 10.1002/ggge.20290.