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@PHDTHESIS{Schumann:192739,
      author       = {Schumann, Kai},
      title        = {{S}trength, {T}extures, {M}icrofabrics and {A}coustic
                      {P}roperties of {A}ctive{P}late {M}argin {S}ediments on- and
                      {O}ffshore {SW} {J}apan},
      school       = {Christian-Albrechts-Universität Kiel},
      type         = {Dr.},
      reportid     = {PUBDB-2014-04278},
      year         = {2014},
      note         = {Christian-Albrechts-Universität Kiel, Diss., 2014},
      abstract     = {Earthquakes are the violent expression of plate motion
                      caused by a sudden release of elastic energy along fault
                      planes known from a variety of tectonic settings. The
                      seismically most active regions on Earth are the subduction
                      zones, where lithospheric plates descend. Especially the
                      Nankai subduction zone southeast of the Japanese islands of
                      Honshu and Shikoku is known for the repeated occurrence of
                      strong earthquakes and devastating tsunamis. The large-scale
                      processes of stick-slip instabilities responsible for
                      earthquake generation are vastly studied, but at least in
                      parts not well understood. This thesis aims to investigate
                      the fundamental processes of faulting and earthquake
                      generation in a setting of converging lithospheric plates.
                      Deformation processes in front of the seismogenic zone and
                      in the accretionary wedge are in the main focus of this
                      work. The question whether the rocks of the Nankai
                      accretionary prisms are capable to produce surface breaks
                      and related tsunamis by brittle faulting, or whether these
                      rocks are capable of distributing deformation within large
                      volumes (slow, stable slip) will be answered. For this
                      purpose, deformation experiments of drill cores from the
                      Nankai accretionary prism were conducted to provide
                      information on the geotechnical properties of the
                      near-surface sediments. Analogue cases exposed along the
                      coast line of Shikoku Island and Boso Peninsula cover those
                      parts in the accretionary prism not accessible by deep sea
                      drilling, so far. Microstructural studies will connect the
                      laboratory data to the natural case. The first study
                      provides a unique dataset of sonic velocities measured
                      during triaxial deformation under laboratory conditions. The
                      slity clay and clayey silt samples were obtained from IODP
                      Expeditions 315, 316 and 333. Seismic time series analysis
                      helped to increase the data quality and to identify
                      erroneous first arrival picks identified by trace-by-trace
                      picking. During axial deformation, the compressional and
                      shear wave velocities (Vp and Vs) range between 1300 –
                      2200 m/s and 150 -800 m/s, respectively. Different
                      velocities were measured for the tectonic settings. Samples
                      from the frontal thrust (accretionary prism toe) show higher
                      Vp compared to the samples from the megasplay fault
                      settings, whereas lowest Vp were measured for the incoming
                      plate sediments, being characterized by higher clay contents
                      compared to the accretionary prism sediments. Generally, Vp
                      increases slightly with increasing effective confining
                      pressure and effective principal stress. Similar
                      observations were made for Vs, irrespective of tectonic
                      setting and composition. Shear, bulk and elastic moduli were
                      calculated from the velocities to differentiate between
                      tectonic settings. The shear moduli ranges between 0.2 –
                      1.3 GPa and the bulk modulus between 3.8 – 8.4 GPa, while
                      the elastic moduli, ranges between 0.5 – 3.8 GPa pointing
                      to over-consolidation of the accretionary prism toe samples
                      and normal consolidation of the footwall of the megasplay
                      fault and incoming plate. The results of Rietveld
                      refinement-based synchrotron texture analysis and
                      microfabric studies of the slity clay and clayey silt
                      samples are reported in the second part of the thesis.
                      Crystallographic preferred orientation (CPO) of illite,
                      kaolinite and smectite basal planes is bedding-parallel and
                      increases with depth. Bedding parallel orientation of the
                      basal planes of the phyllosilicates is preserved in samples
                      tilted by tectonic deformation, indicating progressive
                      burial and compaction as texture forming processes. Shape
                      preferred orientation (SPO) of micropores and detrital
                      illites investigated by Scanning Electron micrographs
                      indicate natural compaction as well. Samples deformed in
                      triaxial experiments differ from these observations as basal
                      planes of phyllosilicates and calcite are oriented almost
                      always perpendicular to the experimental shortening
                      direction. SPO analyses indicate reorientation or flattening
                      of the micropores due to experimental deformation. From
                      these data we show that even in water-rich fine-grained and
                      phyllosilicate rich sediments synchrotron x-ray radiation
                      allows to quantify textures. In the third part, the results
                      of triaxial deformation tests of mudstone samples derived
                      from the tectonically exhumed accretionary prisms belonging
                      to the Boso and Shimanto Belts, representing pre-exhumation
                      burial depths up to 9000 m are presented. To investigate the
                      geomechanical properties of these rocks, pressure stepping
                      tests, constant confining pressure tests and a cyclic
                      loading tests were conducted. To determine the effective
                      shear parameters angle of internal friction and cohesion
                      experimental results were used. Friction angles between 30
                      and 50° are rather high. The sample cohesion for Boso and
                      Shimanto ranges between 2 and 6 MPa and 13 and >30 MPa,
                      respectively. Due to structural and compositional
                      similarities to the Nankai accretionary prism, the results
                      can be used to estimate the geomechanical properties of the
                      deeper parts of the Nankai accretionary prism, which are not
                      accessible by deep sea drilling. The data shows that the
                      forearc rocks are relatively strong. Diagenesis and/ or
                      low-grade metamorphism increase the cohesion. From the data
                      we conclude that stresses up to 18 MPa can be transmitted to
                      the updip limit of the seismogenic zone and between 5 to 13
                      MPa to the actively deforming frontal prism. In the article
                      of Stipp et al. (2013), to which I contributed as co-author,
                      whole-round core samples drilled during IODP Expedition 315,
                      316 and 333 were experimentally deformed in a triaxial cell
                      having been drilled in depths between 28 – 128 m below sea
                      floor (mbsf). During undrained experimental deformation, at
                      400 to 1000 kPa confining pressure, between 0.001 – 9.0
                      mm/min displacement rate, up to $~64\%$ axial compressive
                      strain was reached. Although composition and grain size
                      distribution of the slity clay and clayey silt samples is
                      rather similar, geomechanical data lead to the distinction
                      of two ‘rheological groups’. (1) Structurally weak
                      samples, showing peak deviatoric stress conditions after few
                      percent of compressional strain, continuous stress decrease
                      after peak conditions and contractant behavior (increasing
                      pore pressure) and (2) structurally strong samples, showing
                      continuous strength increase or weaken only moderately at
                      much higher strength levels and higher strains. Strong
                      samples from the accretionary prism toe are
                      overconsolidated, while the weak samples from further
                      upslope are normally consolidated, similar to the samples
                      from the incoming plate. The mechanical state of the
                      décollement can be inferred from the results of the
                      triaxial tests. Up to 18 MPa can be transmitted to the updip
                      limit of the seismogenic zone and up to 13 MPa to the
                      backstop of the active deforming prism. Overconsolidated
                      frontal thrust sediments are able to stable slip and strain
                      partitioning resulting in folding. The middle part of the
                      accretionary prism tends to creep under cyclic loading.
                      Normal consolidated sediments of the megasplay setting are
                      capable to unstable slip and brittle faulting and thus can
                      produce surface breaks. Crystallographic preferred
                      orientation and shape preferred orientation may act as
                      runaway structures transmitting strains to the (near) sea
                      floor.},
      keywords     = {Dissertation (GND)},
      cin          = {DOOR},
      cid          = {I:(DE-H253)HAS-User-20120731},
      pnm          = {DORIS Beamline W2 (POF2-54G13)},
      pid          = {G:(DE-H253)POF2-W2-20130405},
      experiment   = {EXP:(DE-H253)D-W2-20150101},
      typ          = {PUB:(DE-HGF)11},
      urn          = {urn:nbn:de:gbv:8-diss-141164},
      url          = {https://bib-pubdb1.desy.de/record/192739},
}