Open AccessMechanical properties and processes of deformation in shallow sedimentary rocks from subduction zones: An experimental study
Author(s) -
Gadenne Leslie,
Raimbourg Hugues,
Champallier Rémi,
Yamamoto Yuzuru
Publication year - 2014
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1002/2014gc005580
Subject(s) - geology , accretionary wedge , shearing (physics) , overburden pressure , dilatant , sedimentary rock , shear (geology) , deformation (meteorology) , subduction , compaction , deformation mechanism , petrology , shear zone , seismology , geotechnical engineering , mineralogy , geochemistry , tectonics , composite material , materials science , microstructure , oceanography
Abstract To better constrain the mechanical behavior of sediments accreted to accretionary prism, we conducted triaxial mechanical tests on natural samples from the Miura‐Boso paleo‐accretionary prism (Japan) in drained conditions with confining pressures up to 200 MPa as well as postexperiments P‐wave velocity (V p ) measurements. During experiments, deformation is principally noncoaxial and accommodated by two successive modes of deformation, both associated with strain‐hardening and velocity‐strengthening behavior: (1) compaction‐assisted shearing, distributed in a several mm‐wide shear zone and (2) faulting, localized within a few tens of μm‐wide, dilatant fault zone. Deformation is also associated with (1) a decrease in Young's modulus all over the tests, (2) anomalously low V p in the deformed samples compared to their porosity and (3) an increase in sensitivity of V p to effective pressure. We interpret this evolution of the poroelastic properties of the material as reflecting the progressive breakage of intergrain cement and the formation of microcracks along with macroscopic deformation. When applied to natural conditions, these results suggest that the deformation style (localized versus distributed) of shallow (z < a few km) sediments is mainly controlled by the variations in stress/strain rate during the seismic cycle and is therefore independent of the porosity of sediments. Finally, we show that the effect of strain, through cement breakage and microcracks formation, may lower V p for effective pressure up to 40 MPa. As a consequence, the low V p anomalies observed in Nankai accretionary prisms by seismic imaging between 2 and 4 km depth could reflect sediment deformation rather than porosity anomalies.