Shear strength of sediments approaching subduction in the Nankai Trough, Japan as constraints on forearc mechanics

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doi: 10.1002/ggge.20156
Author(s): Ikari, Matt J.; Hüpers, Andre; Kopf, Achim J.
Author Affiliation(s): Primary:
University of Bremen, Center for Marine Environmental Sciences, Bremen, Germany
Volume Title: Geochemistry, Geophysics, Geosystems - G<sup>3</sup>
Source: Geochemistry, Geophysics, Geosystems - G>3`, 14(8), p.2716-2730. Publisher: American Geophysical Union and The Geochemical Society, United States. ISSN: 1525-2027
Note: In English. 79 refs.; illus., incl. sketch map
Summary: The mechanical behavior of the plate boundary fault zone is of paramount importance in subduction zones, because it controls megathrust earthquake nucleation and propagation as well as the structural style of the forearc. In the Nankai area along the NanTroSEIZE (Kumano) drilling transect offshore SW Japan, a heterogeneous sedimentary sequence overlying the oceanic crust enters the subduction zone. In order to predict how variations in lithology, and thus mechanical properties, affect the formation and evolution of the plate boundary fault, we conducted laboratory tests measuring the shear strengths of sediments approaching the trench covering each major lithological sedimentary unit. We observe that shear strength increases nonlinearly with depth, such that the (apparent) coefficient of friction decreases. In combination with a critical taper analysis, the results imply that the plate boundary position is located on the main frontal thrust. Further landward, the plate boundary is expected to step down into progressively lower stratigraphic units, assisted by moderately elevated pore pressures. As seismogenic depths are approached, the decollement may further step down to lower volcaniclastic or pelagic strata but this requires specific overpressure conditions. High-taper angle and elevated strengths in the toe region may be local features restricted to the Kumano transect. Abstract Copyright (2013), . American Geophysical Union. All Rights Reserved.
Year of Publication: 2013
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 18 Geophysics, Solid-Earth; 20 Geophysics, Applied; Asia; Basins; Decollement; Earthquakes; Far East; Fault zones; Faults; Fore-arc basins; Friction; Geophysical methods; Geophysical profiles; Geophysical surveys; Integrated Ocean Drilling Program; Japan; Kumano Japan; Marine geology; NanTroSEIZE; Nankai Trough; North Pacific; Northwest Pacific; Offshore; Pacific Ocean; Plate boundaries; Plate tectonics; Propagation; Rheology; Sediments; Seismic methods; Seismic profiles; Shear strength; Stratigraphic units; Subduction zones; Surveys; West Pacific
Coordinates: N310000 N350000 E1380000 E1320000
Record ID: 2013095574
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