Observations of laboratory earthquake rupture: implications for earthquake early warning

The onset of an earthquake is associated with a nucleation phase, which is necessary to create the conditions for the subsequent dynamic rupture propagation. Theoretical models and laboratory experiments have been proposed to compensate for the lack of direct observations of earthquake nucleation, remaining poorly understood and described through conceptual models. A central and unresolved question is whether and how the nucleation and breakout phases influence the subsequent dynamic rupture propagation and arrest and ultimately determine the final earthquake size. Recent seismological evidence points towards weak determinism between nucleation and final earthquake size. 

Here we present the Mechanics of Earthquakes and Extended Ruptures Apparatus (MEERA) - a horizontal multiaxial apparatus designed to nucleate dynamic instabilities on an experimental fault. The extended size of the fault (30 x 5 cm) enables the simulation of rupture propagation under a controlled environment. This provides an opportunity to study physical controls on final rupture size. Surface and along-fault deformation before and during dynamic instabilities are monitored with the help of digital image correlation and fiber optic sensing. In addition, an array of 12 high frequency (10 MHz) acoustic emission sensors record elastic waves radiated from dynamic instabilities. The aim of experiments on MEERA, part of the wider ERC-FORESEEING project, will be to bring observations on natural earthquake data to the scale of laboratory fractures and to understand whether the onset of acoustic emissions signals follows a similar trend with magnitude as observed for small natural earthquakes. We will present preliminary results of experiments showing the emergence of a critical nucleation length for dynamic rupture propagation during experiments and will discuss the implications of these findings for larger scale natural earthquakes, in the context of Earthquake Early Warning applications.