Fault instability on a finite and planar fault related to early phase of nucleation

Abstract

[1] We numerically investigate the early phase of nucleation on a planar fault with the rate-and state-dependent friction law, loaded externally by steady slip, to clarify its relation to fault instability. We define R n as the invasion distance of the inward creep to characterize that phase. For a circular fault, the dependence of R n on the dimensionless parameters l b , l b−a , and l RA (all of these are proportional to the rigidity and the characteristic distance of the state evolution L and inversely proportional to the normal stress and the fault radius) can be compiled. We found that R n is proportional to l b (both aging law and slip law of the state evolution) and l b−a (aging law). In the case of the aging law only, there are two regimes (ordinary events and slow events) separated by the value of l RA . The regimes have different trend lines, although we could not measure R n for the case of l RA < 0.35 because of breaking of the mirror symmetry of instability along the loading direction. R n in the slow event regime is smaller. Moreover, we investigated the effect of fault shape and found that a model with a long radius along the mode 2 direction has similar parameter dependence to circular faults, but a model with a long radius along the mode 3 direction has different ones. Our results imply that we can qualitatively estimate the fault instability parameters from the early phase of nucleation, although further research is necessary to enable application to actual faults.Citation: Mitsui, Y., and K. Hirahara (2011), Fault instability on a finite and planar fault related to early phase of nucleation,

Slip‐behavior transitions of a heterogeneous linear fault

“…In this case, L cr = 12.7 m, corresponding to η cr ≈ 0.21. From Figure e, we see that the stable‐slip regime ends at η = 0.2 (i.e., a VWZ size of 12 m), and stick slip appears in the VWZ above this value, although the nonseismic stick‐slip regime exists when η = 0.25 (i.e., a VWZ size of 15 m), as reported by Rubin [] and Mitsui and Hirahara []. When a / b is changed to a value of 0.3, the weakening effect at the center of the nucleation zone is about 200 during nucleation period, that is, much larger than unity (Figure S2b), in which case typical nucleation size is L cr ~ 2.7 L b (13.5 m), corresponding to η cr ≈ 0.23, though minimum nucleation size is smaller than that value.…”

“…When the slip law is used with the reference parameter set, although the nucleation size of the VWZ changes with slip velocity [Ampuero and Rubin, 2008], the boundary between the stable-slip regime and the partialseismic regime is the same as for the aging-law case, and the nonseismic stick-slip regime is not observed, as reported by Rubin [2008] and Mitsui and Hirahara [2011]. When a in the VSZ is changed to 0.0015 with the slip law, the same results are obtained as for the aging law.…”

Interval modulation of recurrent slow slip events by two types of earthquake loading

“…To reduce their effects, we set steady-slip zones around the four sides. The procedure for numerical integration is following our previous work (Mitsui and Hirahara 2011).…”

“…The maximal slip velocities of the SSEs are not constant during one interseismic period. It reflects the stress state in the SSE area perturbed by coseismic slip, afterslip, and the early phase of nucleation of the earthquake (e.g., Mitsui and Hirahara 2011). In particular, a latter half of the interseismic period is characterized by the early phase of nucleation.…”

How did the 2011 off the Pacific coast of Tohoku Earthquake start and grow? The role of a conditionally stable area

“…Hence, mechanical models with a rateand state-dependent friction law are useful for considering the generation mechanism of the 2011 Tohoku Earthquake. In particular, these types of mechanical models include the early phase of nucleation (creep propagation from fault edges) during interseismic periods, which is related to fault instability (Mitsui and Hirahara, 2011). The early nucleation could have been detected by geophysical observations, if it had occurred over the whole fault of the M 9 earthquake.…”