Diverse Deformation: Novel Insights into Preparatory Earthquake Physics from the Laboratory

Fault zones in the brittle regime accommodate deformation across a wide range of spatial and temporal scales, from localized, rapid seismic events to extensive, slow aseismic creep.  The initiation of large ruptures is a complex process, with diverse spatiotemporal patterns reflecting a range of physical mechanisms not yet fully integrated into a single theoretical framework.

Recent advances in laboratory experiments, using techniques analogous to seismic and geodetic methods, enable the monitoring of rock deformation across broad scales.  We present results from triaxial rock failure tests employing a novel combination of acoustic emission (AE) sensors (to study seismic response) and fibre optic-based distributed strain sensing (DSS) systems (to map heterogeneous surface strain). A key theoretical challenge is understanding damage accumulation during the pre-failure phase and the transition to seismogenic behaviour.  Our study leverages these technological advances to assess the heterogeneous evolution of rheology and its influence on earthquake preparation physics.

Experiments on intact and notched rock specimens reveal differing preparatory mechanics. In intact specimens, DSS measurements show silent, long-range stress redistribution followed by accelerated AE bursts only at sufficiently high stress levels.  The failure of local heterogeneities produces intermittent changes in AE number and statistics, as well as in surface strain.  In notched specimens, process zones generate self-arresting creep surges with increased AE rates, mirroring natural observations.  We discuss numerical approaches to integrate these diverse behaviours.