The nucleation and rupture processes of giant megathrust earthquakes (M ≥ 9.0) in subduction zones are still controversial. Most previous studies have focused on the subducting plate interface, and the structure beneath the subducting slab and its influence on earthquake generation remain unclear. Here, we present high-resolution seismic velocity tomography beneath six regions where giant earthquakes have occurred. Subslab low-velocity (slow) anomalies are revealed, which may reflect hot mantle upwelling. The giant earthquake hypocentres are generally located above the edges of the slow anomalies or above the gaps between them. Large coseismic slips of the giant earthquakes mainly occurred above gaps between the slow anomalies. We suggest that differential buoyancy force between the slow anomalies and their gaps may be an important factor for earthquake nucleation, and the rupture extent of a giant earthquake may be constrained by the slow anomalies. Hence, it is necessary to conduct seismic tomography to investigate the detailed subslab structure, which may help to pinpoint the potential location and damage zone of a future giant earthquake.
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All data needed to evaluate the conclusions in the paper are provided in the paper and/or the Supplementary Information. All the 3D velocity models may be requested from the authors. The waveform data and P-wave arrival-time data were downloaded free from the Data Management Center of Hi-net and S-net (https://hinetwww11.bosai.go.jp/auth/download/cont/) and the ISC website (http://www.isc.ac.uk/isc-ehb/search/arrivals/).
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We thank the data centres of the Japanese seismic networks and the JMA Unified Earthquake Catalog for providing the high-quality waveform and arrival-time data used for the study of the Japan subduction zone. P.-L. Wang kindly provided her Cascadia slip model. T. Gou provided his Alaska tomographic model. This work was financially supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB42000000) and the National Natural Science Foundation of China (grant no. 41876043, to J.F.) and the Japan Society for the Promotion of Science (grant no. 19H01996, to D.Z.).
The authors declare no competing interests.
Peer review information Nature Geoscience thanks the, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary Handling Editor: Stefan Lachowycz.
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Fan, J., Zhao, D. Subslab heterogeneity and giant megathrust earthquakes. Nat. Geosci. 14, 349–353 (2021). https://doi.org/10.1038/s41561-021-00728-x