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[SCG39-08] Effects of periodic stress perturbations on earthquake nucleation
Keywords:slow earthquake, nonequilibrium statistical physics, nucleation, stress perturbation
One of the crucial methods to discover underlying physics is to investigate a mechanical response. This idea is inherent not only in laboratory scale, but applicable to a kilometer-scale fault [1]. Recent studies have been showing a high susceptibility of tremors in slow earthquake [2], which may be sorted into an issue of the mechanical response. This study numerically investigates effects on earthquake nucleation growths of periodic stress perturbations like ocean tides. By assuming the rate- and state-dependent friction law on a flat fault embedded in an elastic continuum, we compute the earthquake occurrence rate as a function of the stress or the phase of stress perturbation.
The remarkable points in the results are as follows:
(1) The phase distributions do not show a large phase shift.
(2) The earthquake occurrence is defined as the moment when the slip velocity exceeds a given threshold value. The occurrence rate is one-to-one mapped onto the shear or the normal stress at the moment of occurrence. This implies an instantaneous response.
(3) The dependences of occurrence rate on the shear or the normal stress appear to be exponential. This indicates existence of a characteristic stress.
(4) Variation of the normal stress additionally alters a frictional state on the interface according to the rock experiments performed by Linker and Dieterich [3], but this Linker-Dietrich effect on the stress response has not been well understood yet. As a result of numerical simulation, the Linker-Dieterich effect is found to suppress a difference in value of the phase distributions. Eventually, if the effect is very large, we observe even antiphase distribution (see fig. 1).
[1] T. J. Ader, N. Lapusta, J.-P. Avouac, and J.-P. Ampuero, Geophys. J. Int. 198, 385 (2014).
[2] S. Ide and Y. Tanaka, Geophys. Res. Lett. 41, 3842 (2014); S. Ide, S. Yabe, H.-J. Tai, and K. H. Chen,
Geophys. Res. Lett., 42, 3248 (2015).
[3] M. F. Linker, J. H. Dieterich, J. Geophys. Res. 97 4923 (1992).
The remarkable points in the results are as follows:
(1) The phase distributions do not show a large phase shift.
(2) The earthquake occurrence is defined as the moment when the slip velocity exceeds a given threshold value. The occurrence rate is one-to-one mapped onto the shear or the normal stress at the moment of occurrence. This implies an instantaneous response.
(3) The dependences of occurrence rate on the shear or the normal stress appear to be exponential. This indicates existence of a characteristic stress.
(4) Variation of the normal stress additionally alters a frictional state on the interface according to the rock experiments performed by Linker and Dieterich [3], but this Linker-Dietrich effect on the stress response has not been well understood yet. As a result of numerical simulation, the Linker-Dieterich effect is found to suppress a difference in value of the phase distributions. Eventually, if the effect is very large, we observe even antiphase distribution (see fig. 1).
[1] T. J. Ader, N. Lapusta, J.-P. Avouac, and J.-P. Ampuero, Geophys. J. Int. 198, 385 (2014).
[2] S. Ide and Y. Tanaka, Geophys. Res. Lett. 41, 3842 (2014); S. Ide, S. Yabe, H.-J. Tai, and K. H. Chen,
Geophys. Res. Lett., 42, 3248 (2015).
[3] M. F. Linker, J. H. Dieterich, J. Geophys. Res. 97 4923 (1992).