Susceptibility of microseismic triggering to small sinusoidal stress perturbations at the laboratory scale

Abstract

Stresses exerted on faults are constantly subjected to fluctuations related to the periodicity of external forces applied to the Earth's crust, for example, tidal forces, or seasonal variations in water loads. These stress variations have been linked to time periods when earthquakes are more likely to occur in some specific contexts, but the precise mechanisms at play are not fully understood. Experimental work is here conducted to examine the influence of several key parameters, namely oscillation period and amplitude and background tectonic velocity, on the occurrence of laboratory-scale microseismicity. Microseismicity periodicity is proportional to the stress oscillation amplitude, and both short oscillation period and low tectonic velocity cause microseismicity to correlate less with the stress oscillations, possibly explaining why short-period tides do not correlate well with seismicity whereas long-period seasonal variations in stress have been shown to correlate with seismicity. The ratio between small and large events also appears to correlate with the stress oscillation, suggesting that stress oscillations might create conditions during which large events are more likely to occur.