Foreshock properties illuminate nucleation processes of slow and fast laboratory earthquakes

Abstract

Abstract Understanding the connection between seismic activity and the earthquake nucleation process is a fundamental goal in earthquake seismology with important implications for earthquake early warning systems and forecasting. We use high-resolution acoustic emission (AE) waveform measurements from laboratory stick-slip experiments that span a spectrum of slow to fast slip rates to probe laboratory foreshocks and nucleation. We measure the waveform similarity of AE templates and use differential travel-times to track their relative locations. Fast laboratory earthquakes are preceded by a late, rapid increase in waveform similarity prior to failure, whereas slow slip events show a modest increase in waveform similarity before failure. Differential travel-time and waveform similarity measurements reveal a spatiotemporal coalescence of foreshocks prior to failure. Our work suggests that laboratory foreshocks evolve systematically prior to stick-slip failure and are a byproduct of a slow nucleation process driven by pre-seismic fault slip.