Experimental analysis of semi-brittle deformation: Implications for deformation dynamics

Abstract

Faults can release energy via a variety of different slip mechanisms ranging from steady creep to fast and destructive earthquakes. Tying the rheology of the crust to various slip dynamics is important for our understanding of plate tectonics and earthquake generation. Here, we propose that the interplay of fractures and viscous flow leads to a spectrum between stick-slip and creep. We use an elasto-visco-plastic rock analog (Carbopol U-21) where we vary the yield stress to investigate its impact on slip dynamics in shear experiments. The experiments are performed using a simple shear apparatus, which provides distributed shear across the entire width of the experiment and allows in situ observations of deformation. We record force and displacement during deformation and use time lapse photography to document fracture development. A low yield stress (25 Pa) leads to creep dynamics in the absence of fractures. An intermediate yield stress (144 Pa) leads to the development and interaction of opening (mode I)and shear (mode II) fractures. This interaction leads to a spectrum in slip dynamics ranging from creep to stick-slip. A high yield stress (357 Pa) results in the development of many mode I fractures and a deformation signal dominated by stick-slip. These results show that bulk yield stress, fracture formation, and slip dynamics are closely linked and can lead to a continuum between creep and stick-slip. We suggest that rheology should be considered as an additional mechanism to explain the broad range of slip dynamics in natural faults.