Abstract
Giant megathrust earthquakes typically occur above the upper-plate Moho or the 350°C isotherm in warm subduction zones. However, large earthquakes also occur within the mantle wedge corner at 35-55 km depth at cold subduction zones, such as the Kermadec, Japan Trench, and Chilean margins. Here we investigate the frictional behavior of lawsonite blueschist metagreywacke, potentially found in cold subduction channels, to better understand the control of metamorphic grade on such first-order variations in seismogenic depth. We perform velocity-step experiments on metagreywacke gouge from room temperature to 500°C and effective normal stresses from 50 MPa to 320 MPa, capturing the unstable friction regime and the brittle-to-flow transition. The constitutive behavior of metagreywacke indicates a potential seismogenic behavior at high temperatures below the Moho. Large megathrust earthquakes in the mantle wedge corner may develop in the lawsonite blueschist metasediment channel of cold subduction slabs.
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Data availability
The laboratory data used in this study are available in a zenodo.org repository83.
Code availability
A demonstration code for simulating velocity-step experiments using the constitutive law proposed in this study is available at https://doi.org/10.5281/zenodo.1852974983. The “Unicycle” software package, along with the input files for the seismic cycle simulation, can be accessed at: https://bitbucket.org/sbarbot/unicycle.
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Acknowledgements
We are grateful for the technical support of Wenming Yao and Changrong He at the Institute of Geology, China Earthquake Administration. This study is funded by the National Natural Science Foundation of China under grant 42274234, the National Key Research and Development Program of China (2022YFC3003704), and the National Science Foundation under award number EAR-1848192. H.Z. acknowledges support from the National Science Foundation grant EAR-2041892 awarded to John E. Vidale.
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S.B., H.Z., and L.Z. conceptualized the study. H.Z. and Z.Y. conducted the deformation experiments. H.Z. and S.B. processed the original laboratory data. J.P. conducted the thin section analysis. L.Z. conducted the SEM analysis. H.Z., S.B., M.L. and L.Z. conducted the data analysis. H.Z. and S.B. produced the original manuscript. All the authors reviewed the manuscript.
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Zhang, H., Barbot, S., Yang, Z. et al. Large megathrust earthquakes in cold mantle wedge corners under lawsonite blueschist facies. Nat Commun (2026). https://doi.org/10.1038/s41467-026-70315-4
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DOI: https://doi.org/10.1038/s41467-026-70315-4
