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Experimental evidence that thrust earthquake ruptures might open faults


Many of Earth’s great earthquakes occur on thrust faults1. These earthquakes predominantly occur within subduction zones, such as the 2011 moment magnitude 9.0 eathquake in Tohoku-Oki, Japan, or along large collision zones, such as the 1999 moment magnitude 7.7 earthquake in Chi-Chi, Taiwan2. Notably, these two earthquakes had a maximum slip that was very close to the surface3,4. This contributed to the destructive tsunami that occurred during the Tohoku-Oki event and to the large amount of structural damage caused by the Chi-Chi event. The mechanism that results in such large slip near the surface is poorly understood as shallow parts of thrust faults are considered to be frictionally stable5. Here we use earthquake rupture experiments to reveal the existence of a torquing mechanism of thrust fault ruptures near the free surface that causes them to unclamp and slip large distances. Complementary numerical modelling of the experiments confirms that the hanging-wall wedge undergoes pronounced rotation in one direction as the earthquake rupture approaches the free surface, and this torque is released as soon as the rupture breaks the free surface, resulting in the unclamping and violent ‘flapping’ of the hanging-wall wedge. Our results imply that the shallow extent of the seismogenic zone of a subducting interface is not fixed and can extend up to the trench during great earthquakes through a torquing mechanism.

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Figure 1: A thrust fault modelled by dividing a rectangular plate with an angled cut.
Figure 2: A typical sub-Rayleigh rupture (P = 2.5 MPa) is chronologically portrayed at experimental times t = 58.5, 63.5, and 93.5 μs.
Figure 3: Recorded fault slip (vslip) and opening velocity (vopen).


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We gratefully acknowledge the National Science Foundation (award number EAR-1321655), which has supported this research. We also acknowledge our colleague, N. Lapusta (California Institute of Technology) for comments and advice. H.S.B. acknowledges K. Kiara and A. Schubnel for inspiring this work.

Author information




A.J.R., R.M. and H.S.B. concieved the study and designed the experiments. V.G. and A.J.R. conducted the experiments. R.M. and H.S.B. conducted numerical modelling studies. All authors contributed to analysis, interpretation and manuscript preparation.

Corresponding author

Correspondence to Harsha S. Bhat.

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The authors declare no competing financial interests.

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Reviewer Information Nature thanks C. Scholz and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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Gabuchian, V., Rosakis, A., Bhat, H. et al. Experimental evidence that thrust earthquake ruptures might open faults. Nature 545, 336–339 (2017).

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