Earthquake-induced transformation of the lower crust


The structural and metamorphic evolution of the lower crust has direct effects on the lithospheric response to plate tectonic processes involved in orogeny, including subsidence of sedimentary basins, stability of deep mountain roots and extension of high-topography regions. Recent research shows that before orogeny most of the lower crust is dry, impermeable and mechanically strong1. During an orogenic event, the evolution of the lower crust is controlled by infiltration of fluids along localized shear or fracture zones. In the Bergen Arcs of Western Norway, shear zones initiate as faults generated by lower-crustal earthquakes. Seismic slip in the dry lower crust requires stresses at a level that can only be sustained over short timescales or local weakening mechanisms. However, normal earthquake activity in the seismogenic zone produces stress pulses that drive aftershocks in the lower crust2. Here we show that the volume of lower crust affected by such aftershocks is substantial and that fluid-driven associated metamorphic and structural transformations of the lower crust follow these earthquakes. This provides a ‘top-down’ effect on crustal geodynamics and connects processes operating at very different timescales.

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Fig. 1: Earthquakes and aftershocks in the lower crust.
Fig. 2: Fossil earthquakes in the Bergen Arcs.
Fig. 3: Transformation of the lower crust.


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This project has been supported by the European Union’s Horizon 2020 Research and Innovation Programme under ERC Advanced Grant Agreement number 669972, ‘Disequilibrium Metamorphism’ (‘DIME’; to B.J.), and by the Norwegian Research Council grant number 250661 (‘HADES’; to F.R.). Y.B.-Z. acknowledges support from the National Science Foundation (grant EAR-1722561). The paper benefited from discussions with and comments by I. Zaliapin, J. Jackson, A. Putnis, S. Schmalholz, S. Xu, P. Meakin and J. Platt.

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Nature thanks B. Yardley and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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All authors designed this study. B.J. and Y.B.-Z. wrote the manuscript with input from F.R. and H.A., H.A. and B.J. conducted the field studies, F.R. designed the figures. Y.B.-Z. and F.R. derived the theoretical estimates of earthquake quantities motivated by the idea of ‘seismic index’ proposed by H.A.

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Correspondence to Bjørn Jamtveit.

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Extended data figures and tables

Extended Data Fig. 1 Rheology of dry anorthite.

Shear stress versus temperature diagram contoured with respect to strain rate.

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Jamtveit, B., Ben-Zion, Y., Renard, F. et al. Earthquake-induced transformation of the lower crust. Nature 556, 487–491 (2018).

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