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P and S wave velocity measurements of water‐rich sediments from the Nankai Trough, Japan
Author(s) -
Schumann Kai,
Stipp Michael,
Behrmann Jan H.,
Klaeschen Dirk,
SchulteKortnack Detlef
Publication year - 2014
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1002/2013jb010290
Subject(s) - geology , accretionary wedge , subduction , overburden pressure , shear (geology) , seismology , silt , s wave , mineralogy , drilling , tectonics , petrology , geotechnical engineering , geomorphology , materials science , metallurgy
Acoustic velocities were measured during triaxial deformation tests of silty clay and clayey silt core samples from the Nankai subduction zone (Integrated Ocean Drilling Program Expeditions 315, 316, and 333). We provide a new data set, continuously measured during pressure increase and subsequent axial deformation. A new data processing method was developed using seismic time series analysis. Compressional wave velocities ( V p ) range between about 1450 and 2200 m/s, and shear wave velocities ( V s ) range between about 150 and 800 m/s. V p slightly increases with rising effective confining pressure and effective axial stress. Samples from the accretionary prism toe show the highest Vp , while fore‐arc slope sediments show lower Vp . Samples from the incoming plate, slightly richer in clay minerals, have the lowest values for V p . V s increases with higher effective confining pressures and effective axial stress, irrespective of composition and tectonic setting. Shear and bulk moduli are between 0.2 and 1.3 GPa, and 3.85 and 8.41 GPa, respectively. Elastic moduli of samples from the accretionary prism toe and the footwall of the megasplay fault (1.50 and 3.98 GPa) are higher than those from the hanging wall and incoming plate (0.59 and 0.88 GPa). This allows differentiation between normal and overconsolidated sediments. The data show that in a tectonosedimentary environment of only subtle compositional differences, acoustic properties can be used to differentiate between stronger (accretionary prism toe) and weaker (fore‐arc slope, incoming plate) sediments. Especially V p / V s ratios may be instrumental in detecting zones of low effective stress and thus high pore fluid pressure.