Experimental evidence that thrust earthquake ruptures might open faults

• Published in: Nature (London) Vol. 545; no. 7654; pp. 336 - 339
• Main Authors: Gabuchian, Vahe, Rosakis, Ares J., Bhat, Harsha S., Madariaga, Raúl, Kanamori, Hiroo
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 18.05.2017; Nature Publishing Group
• Subjects: 704/2151/508; 704/2151/562; 704/4111; Aircraft components; Amplification; Asymmetry; Compression; Ear; Earthquakes; Fault lines; Faults (Geology); Finite element method; Flapping; Foams; Fracture mechanics; Free surfaces; Friction; Geological faults; Geology; Humanities and Social Sciences; Information processing; Interfaces; Laboratories; Laboratory experiments; letter; Locks; Lubrication; Mathematical models; Mimicry; multidisciplinary; Nucleation; Numerical models; Numerical simulations; Photoelasticity; Planets; Rayleigh waves; Rubber; Rupture; Science; Seismic activity; Seismicity; Seismological research; Separation; Simulation; Stress waves; Thrust; Torque; Tsunamis; Velocity; Velocity measurement; Wave propagation; Wedges; United States > US; Taiwan; California
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature22045

Earthquake rupture experiments and mathematical modelling reveal the existence of a torquing mechanism of thrust fault ruptures near the free surface that causes them to dynamically unclamp, open and slip large distances. The thrust of the matter Many large earthquakes occur on thrust faults, such as the devastating 2011 Tohoku-Oki earthquake in Japan and the 1999 Chi-Chi earthquake in Taiwan, both of which had their maximum slip unusually close to Earth's surface. Vahe Gabuchian et al. present earthquake rupture experiments that reveal the existence of a torquing mechanism of thrust fault ruptures near the surface that can unclamp the thrust faults, enabling them to slip large distances. Numerical modelling of the experiments shows that the hanging-wall wedge undergoes pronounced rotation in one direction as the earthquake rupture approaches the surface. This torque is released as soon as the rupture breaks the surface, resulting in the unclamping and violent 'flapping' of material above the fault. Many of Earth’s great earthquakes occur on thrust faults 1 . 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, Taiwan 2 . Notably, these two earthquakes had a maximum slip that was very close to the surface 3 , 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 stable 5 . 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.