Collaborative Research: Experimental analysis of strain transients in a heterogeneous semi-brittle system: Implications for tectonics

Iowa State University, Ames IA

Investigators

Abstract

Tectonic motions give rise to destructive earthquakes and to enigmatic slower slip events on fault zones. Brittle behavior and friction laws that describe slip over fractured or rough fault surfaces do not account for the fact that fault zones can simultaneously break in a brittle manner and flow in a ductile way as has been observed in the geologic record. This project combines laboratory experiments and theoretical analysis on the effect a semi-brittle material can have on the mechanisms of deformation localization and slip accumulation, which may provide critical insights on the mechanics of earthquakes. This project proposes that the wide variation in deformation speeds from earthquake to steady creep can be explained by the interaction of brittle fracturing and ductile flow in a semi-brittle material. This behavior will be explored with physical experiments using Carbopol, which exhibits both brittle and ductile deformation simultaneously. The experiments will test whether the interaction of tensional and shear fractures in a semi-brittle material leads to strain transients, or if, alternatively, the re-occurring strain transients are controlled by the strength along the shear fracture such that the formation of the fractures only appears to be concurrent with the slip. The results will be incorporated into an analytical model, which allows extrapolating the results to time scales relevant to strain transients in Earth. The work proposed here will fundamentally advance the understanding of semi-brittle deformation and its impact on strain transients.