Elastic properties of water-rich sediments from the Nankai accretionary prism.

Schumann, Kai, Stipp, Michael, Klaeschen, Dirk and Behrmann, Jan (2011) Elastic properties of water-rich sediments from the Nankai accretionary prism. [Poster] In: 71. Jahrestagung der Deutschen Geophysikalischen Gesellschaft gemeinsam mit der Arbeitsgemeinschaft Extraterrestrische Forschung. , 21.-24.02.2011, Köln .

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IODP expeditions 315 and 316 investigated the shallow frontal thrusts and the hanging wall to a major active splay fault of the Nankai accretionary prism. We analyze the composition, the microstructure and the deformation behavior of a drill core sample set from depths up to 398 m below sea floor in order to quantify their influence on the elastic properties of these sediments. The uniform silty clay samples consist of ~40 % clay minerals, 25 % quartz, 25 % feldspar, and 10 % calcite. Geotechnical experiments indicate that samples from the hanging wall of the major splay fault are structurally weak, while samples from the prism toe behave structurally strong with peak deviatoric stresses of 1300 kPa. Ultrasonic p- and s-wave velocity measurements were carried out during reconsolidation and during shear testing yielding velocities of 700 – 1800 m/s for the p-waves and 400 – 1000 m/s for the s-waves. Problems in the incorrect first arrival detection time of an automatic single trace algorithm were identified by sorting the time series data into common shear test gathers. By seismic time series analysis primary, multiple, and converted phase could be identified. Manually picked travel times in the common shear test gathers were used to calculate propagation velocity variations for each experiment. Based on these velocity data refinements, systematic changes in the elastic properties can be determined and correlated to changes in bulk density of the samples, a collapsing pore space and to a lesser extent to compositional and microstructural differences between the samples.

Document Type: Conference or Workshop Item (Poster)
Keywords: Geodynamics
Research affiliation: OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-GDY Marine Geodynamics
Projects: NEXT
Date Deposited: 04 Jul 2011 10:45
Last Modified: 23 Feb 2012 06:13
URI: http://oceanrep.geomar.de/id/eprint/11957

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