Fault contact evolution seen via total internal reflection and heard via acoustic emissions

Earthquakes and ice sheet collapse are significant hazards that are both governed by friction. Fault interfaces and glacier beds share many frictional behaviours: slip stability and instability, seismicity, healing, and episodic slip. Rate-and-state friction (RSF), an empirically derived framework for describing frictional strength, has been successfully utilized for the last five decades to quantitatively characterize earthquake phenomena and has more recently been employed to describe stick-slip behaviour of glaciers. While RSF has been used to extract consistent parameters in both systems, frictional behaviours are rooted in the evolution of the asperities in contact at the interface. Although RSF is powerful (and practical!), it does not reveal the micromechanisms driving the behaviour it describes, nor does it account for other behaviours, such as rupture initiation and variation in stress drop. For this reason, we take advantage of the transparency of ice, its faster deformation timescales, as well as the frictional properties ice shares with rock, to directly observe the frictional interface in situ during shear. To do this, we employ a novel adaptation to our cryogenic biaxial device. As the interface cycles between periods of holds and shears, we use 1) an optical technique, total internal reflection, to light up the interface contacts and observe their evolution, and 2) acoustic emission sensors to listen to and locate slip events. This unique combination of data will allow us to more comprehensively understand the contact-level mechanisms that control friction on deforming interfaces, and help us to better interpret the seismological data we measure on faults and ice sheets. Here, we present recent results of this work.