Laboratory investigation of conditions of slow slip event generation

Abstract:

The problem of slow slip event generation was studied in laboratory experiments on a slider model. In the experiments a granite block 8×8×3 cm in size was put on an immovable granite basement. The contact gap between the block and the basement was filled with a layer of granular materials. The block was moved by a spring element with the stiffness of 20-50 kN/m and the rate of spring deformation of 0.1 – 20 mcm/s. Shear-induced signals of acoustic emission (AE) were registered by velocimeters in the bandwidth of 30-500 kHz.

A full spectrum of slip modes was realized – from creep to regular stick-slip, each accompanied by AE signals with different waveforms. Different slip modes can be realized both in the way of quasi-regularly repeated events and in the way of stochastic events. During shear the deformation characteristics of interblock contact and acoustic emission parameters continuously change [1, 2]. We have found that peculiarities of shear deformation and observed acoustic portrait are defined by interblock contact structure on the mesoscale, while variations of stress-strain state are of secondary importance.

The results of laboratory experiments allow to consider the process of shear deformation of a gouge-filled fault as the evolution of a self-organized dynamic system, and the macroscopic slip events – as the final stage of self-organization process. Basing on the results of experiments a new geomechanical model of different slip mode generation was developed. The model shows that different slip modes form a continuous set and allows to reveal the conditions of generation of different slip modes on faults. It was determined that generation of slow slip events may be provoked both by peculiarities of spatial structure of the fault zone and by rheological properties of the gouge.

 The work is supported by the Russian Science Foundation (grant no. 14-17-00719).

[1] G.G. Kocharyan, A.A. Ostapchuk (2011). Doklady Earth Sciences. 441-1, 1591-1594.

[2] A.A. Ostapchuk, D.V. Pavlov (2015). AIP Conference Proceedings, 1683, 020169.