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Locking of the Chile subduction zone controlled by fluid pressure before the 2010 earthquake

Abstract

Constraints on the potential size and recurrence time of strong subduction-zone earthquakes come from the degree of locking between the down-going and overriding plates, in the period between large earthquakes. In many cases, this interseismic locking degree correlates with slip during large earthquakes1,2,3,4 or is attributed to variations in fluid content at the plate interface5. Here we use geodetic and seismological data to explore the links between pore-fluid pressure and locking patterns at the subduction interface ruptured during the magnitude 8.8 Chile earthquake in 2010. High-resolution three-dimensional seismic tomography reveals variations in the ratio of seismic P- to S-wave velocities (Vp/Vs) along the length of the subduction-zone interface. High Vp/Vs domains, interpreted as zones of elevated pore-fluid pressure, correlate spatially with parts of the plate interface that are poorly locked and slip aseismically. In contrast, low Vp/Vs domains, interpreted as zones of lower pore-fluid pressure, correlate with locked parts of the plate interface, where unstable slip and earthquakes occur. Variations in pore-fluid pressure are caused by the subduction and dehydration of a hydrothermally altered oceanic fracture zone. We conclude that variations in pore-fluid pressure at the plate interface control the degree of interseismic locking and therefore the slip distribution of large earthquake ruptures.

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Figure 1: The Maule earthquake and distributions of locking and Vp/Vs ratio at the study area.
Figure 2: Spatial correlation between locking degree and Poisson’s ratio.
Figure 3: Fluid pressure ratio and locking degree relationship.
Figure 4: Conceptual diagram of fluid sources and transport in the plate-interface region.

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Acknowledgements

We thank A. Nur for advice regarding the stress calculation. We also thank M. Rosenau, J. Bedford, E. Contreras-Reyes and H. Sone for comments and discussions on the manuscript. We are grateful to H. Perfettini for his review and comments, which helped to improve the manuscript. This work was supported in part by the MARISCOS MO/2310/1-1 project of the German Research Foundation (DFG). The seismic data were acquired with instruments of the Geophysical Instrument Pool (GIPP).

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Contributions

C.H. and A.R. constructed the 3D tomography and conducted the synthetic resolution tests. O.O. developed the conceptual idea of the study. M.M carried out the locking and pore-fluid pressure calculations. O.H. was involved in the investigation of effective stress, pore-fluid pressure and mechanical interpretations. S.A. contributed to the petrological interpretation, conceptual model, pore-fluid calculations and figure design. All authors discussed the results and implications and shared in writing the manuscript.

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Correspondence to Marcos Moreno.

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The authors declare no competing financial interests.

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Moreno, M., Haberland, C., Oncken, O. et al. Locking of the Chile subduction zone controlled by fluid pressure before the 2010 earthquake. Nature Geosci 7, 292–296 (2014). https://doi.org/10.1038/ngeo2102

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