Publication Date:
2016-08-01
Description:
Ocean-floor carbonate-and clay-rich sediments form major inputs to subduction zones, especially at low-latitude convergent plate margins. Therefore, knowledge of their frictional behaviour is fundamental for understanding plate-boundary earthquakes. Here we report results of mechanical tests performed on simulated fault gouges prepared from ocean-floor carbonates and clays, cored during IODP drilling offshore Costa Rica. Clay-rich gouges show internal friction coefficients (that is, the slope of linearized shear stress versus normal stress data) of μ int = 0.44 â ' 0.56, irrespective of temperature and pore-fluid pressure (P f). By contrast, μ int for the carbonate gouge strongly depends on temperature and pore-fluid pressure, with μ int decreasing dramatically from 0.84 at room temperature and P f = 20 MPa to 0.27 at T = 140 °C and P f = 120 MPa. This effect provides a fundamental mechanism of shear localization and earthquake generation in subduction zones, and makes carbonates likely nucleation sites for plate-boundary earthquakes. Our results imply that rupture nucleation is prompted by a combination of temperature-controlled frictional instability and temperature-and pore-pressure-dependent weakening of calcareous fault gouges. © 2016 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
Print ISSN:
1752-0894
Electronic ISSN:
1752-0908
Topics:
Geosciences
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