Journal
NATURE GEOSCIENCE
Volume 9, Issue 9, Pages 717-+Publisher
NATURE PUBLISHING GROUP
DOI: 10.1038/NGEO2774
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Funding
- Deutsche Forschungsgemeinschaft (DFG) [STI298/7-1, STI298/7-2]
- Netherlands Organisation for Scientific Research (NWO) through a VIDI grant [854.12.011]
- ERC starting grant SEISMIC [335915]
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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 mu(int) = 0.44-0.56, irrespective of temperature and pore-fluid pressure (P-f). By contrast, mu(int) for the carbonate gouge strongly depends on temperature and pore-fluid pressure, with mu(int) decreasing dramatically from 0.84 at room temperature and P-f = 20MPa to 0.27 at T = 140 degrees C and P-f = 120MPa. 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.
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