Paradox in Rupture Propagation Velocity
Abstract
Recently, there are some experimental reports that the rupture can propagate faster than the P wave velocity (termed supersonic rupture). Gori et al. (2018) observed supersonic rupture propagation along a polymeric material interface by identifying the shock wave front of P waves with the high speed DIC measurement. Such apparent violation of causality can be reconciled by invoking a strain-rate-dependence of material wave velocity, such that the observed rupture propagation velocity is still below the highest P wave velocity ahead of the rupture tip.
On the other hand, Fukuyama et al. (2019) found emergent slow slip (EMS) events that propagate faster than the P wave velocity during the meter-scale biaxial rock friction experiments. Unlike the case of using external energy supply to help initiate supersonic rupture in Gori et al. (2018), Fukuyama et al. (2019)'s data indicated that the supersonic rupture could occur even without large external energy supply. This could be achieved since the onset of the EMS rupture was very gentle and only a small amount of energy was consumed at the rupture front. Nevertheless, wave radiation was observed, which could be considered as a sort of shock waves generated at the supersonic rupture front. If we assume that the EMS events occurred on a zero-thickness boundary between two elastic rock specimens, all materials will behave elastically and all information has to propagate with elastic wave velocity. In this case, the rupture velocity cannot exceed the elastic wave velocity. In contrast, when a thin layer exists on the fault, which sheared during the EMS events, the thin layer could be deformed nonlinearly with locally high strain rates as Fukuyama et al. (2019) proposed. In this case, the rupture can propagate faster than the elastic wave velocities of the surrounding medium. These recent experimental observations raise a paradox with regard to rupture propagation velocity, which seemed difficult to resolve by the classical fracture mechanics theories. We, therefore, need to construct physical models to explain these new phenomena.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.S41B..01F
- Keywords:
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- 5199 General or miscellaneous;
- PHYSICAL PROPERTIES OF ROCKS;
- 7209 Earthquake dynamics;
- SEISMOLOGY;
- 7215 Earthquake source observations;
- SEISMOLOGY;
- 7290 Computational seismology;
- SEISMOLOGY