The onset of laboratory earthquakes explained by nucleating rupture on a rate‐and‐state fault

• Published in: Journal of geophysical research. Solid earth Vol. 121; no. 8; pp. 6071 - 6091
• Main Authors: Kaneko, Yoshihiro, Nielsen, Stefan B., Carpenter, Brett M.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-08-2016
• Subjects: Acceleration; earthquake nucleation; Earthquake prediction; Earthquakes; Energy balance; Experiments; Fault lines; Fault zones; Faults; Fluid pressure; frictional sliding; Geological faults; Geophysics; Griffith Irwin fracture; Interfaces; Laboratories; laboratory earthquakes; Laboratory experimentation; Laboratory experiments; Load distribution; Loading rate; Mathematical models; Normal stress; Nucleation; Numerical models; P-waves; Phases; Precursors; Propagation; rate‐and‐state friction; Rupture; Scaling; Seismic activity; Seismic wave propagation; Seismic waves; slow rupture; Stress propagation; Wave propagation
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1002/2016JB013143

Precursory aseismic slip lasting days to months prior to the initiation of earthquakes has been inferred from seismological observations. Similar precursory slip phenomena have also been observed in laboratory studies of shear rupture nucleation on frictional interfaces. However, the mechanisms that govern rupture nucleation, even in idealized laboratory settings, have been widely debated. Here we show that a numerical model incorporating rate‐and‐state friction laws and elastic continuum can reproduce the behaviors of rupture nucleation seen in laboratory experiments. In particular, we find that both in laboratory experiments and simulations with a wide range of normal stresses, the nucleation consists of two distinct phases: initial slow propagation phase and faster acceleration phase, both of which are likely aseismic processes, followed by dynamic rupture propagation that radiates seismic waves. The distance at which the rupture transitions from the initial slow phase to the acceleration phase can be roughly predicted by a theoretical estimate of critical nucleation length. Our results further show that the critical nucleation length depends on the background loading rate. In addition, our analysis suggests that critical nucleation length and breakdown power derived from the Griffith crack energy balance control the scaling of nucleating ruptures. Moreover, the background loading rate and loading configuration significantly affect the rupture propagation speed. Furthermore, if the same nucleation mechanism applies to natural faults, the migration speed of foreshocks triggered by the propagation of slow rupture within the nucleation zone would depend on the effective normal stress and hence fluid pressure in the fault zone.
Key Points
Nucleation process of laboratory earthquakes is quantitatively reproduced by relatively simple, rate‐and‐state fault model
Critical nucleation length and breakdown power density control the scaling of nucleating ruptures in laboratory experiments
Loading rate or configuration significantly affects the propagation speeds of slow rupture front